Elmcare.com - All about elm trees and elm tree care.

Transcription

Home | Elm Care Products | Register your Elm | Forum
Last Update 17/12/01
Customized Elm Tree Care Kits
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Custom care kits include
specialized and innovative soil
treatments designed to promote
root development and the longterm health and vitality of your
elm. A healthier elm will be
better able to fight against Dutch elm disease.
more
Quick Elm Facts
Elm Tree Registry
Visit TreeHelp.com for
all of your tree and shrub
care needs
Register your elm tree to receive customized care
advice...more.
Return of the Stately Elm
Writer and broadcaster Jamie Swift examines the
Canadian city of Winnipeg's struggle to combat
Dutch elm disease. Through the work of community
groups like the Coalition to Save the Elms and
innovative technology, the city has achieved
substantial success... more.
http://www.elmcare.com/index.htm (1 of 2) [2/27/02 10:29:57 PM]
Did you know a new wild
bird seed has been
developed and tested that
actually repels squirrels?
Click here to learn about
Squirrel Proof Wild Bird
Seed.
New Treatments for
Dutch Elm Disease?
Researchers examine new ways to
fight this devastating disease.
Elms in History
Elm Tree Links
Look at elms in the context of
human history.
Links to a growing community of
academics, homeowners and
professional tree care experts.
Elms in Literature
Quick Elm Facts
Elm Species
Elms come in many sizes and
shapes...learn about them all.
Read what some of the world's
leading poets and authors have
written of the elm.
Thank you for visiting Elmcare.com!
Site Map | About this site | Home
Tree Registry | www.TreeHelp.com
Copyright
http://www.elmcare.com/index.htm (2 of 2) [2/27/02 10:29:57 PM]
Discover something new and
interesting about the elm.
How Trees Work
Home > How Trees Work
How Trees Work
What is a ring-porous vascular system?
What is the difference between wild-type
and cloned trees?
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Find the answers to these questions and
more by clicking on one of the topics below:
More Info...
Important Facts
Types of Trees
Structure of a Tree
How Trees Drink
How Trees Breathe
Copyright
http://www.elmcare.com/trees/how_trees_work.htm [2/27/02 10:30:02 PM]
Types of Trees
Home > How Trees Work > Types of Trees
Angiosperms vs. Gymnosperms
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
Trees are scientifically divided into two major categories: angiosperms and
gymnosperms.
Angiosperms are flowering plants and their seeds are encased in a protective
ovary. This division contains the larger number of species can be further
subdivided into dicots and monocots. Dicots have two seed leaf structures and
include many broadleaf trees such as the elm, maple and oak. Monocots have
one seed leaf structure and include species such as the palm.
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Gymnosperms, on the other hand, do not produce flowers. Their seeds have
structures such as cones, rather than a protective ovary. Conifers (needle-leaf
trees) are a major group of gymnosperms.
Quick Elm Facts
Deciduous vs. Coniferous
Trees can also be divided into deciduous and coniferous categories.
Deciduous trees are also known as broadleaf trees because the leaves are
generally larger and wider than those of conifers. The larger leaf size means a
greater surface area for photosynthesis, but it also mean the leaf is too fragile to
withstand winter conditions. Therefore, most deciduous trees drop their leaves in
autumn.
Coniferous trees keep their leaves throughout the year, shedding only the oldest
leaves. Usually these leaves are lower down on the tree and do not receive as
much sunlight as newly developed leaves higher up. Some of the best-known
members of the conifer family are pines, spruces, firs, and hemlocks. The cones of
the conifers are its flowers.
http://www.elmcare.com/trees/types_of_trees.htm (1 of 2) [2/27/02 10:30:04 PM]
Types of Trees
Copyright
http://www.elmcare.com/trees/types_of_trees.htm (2 of 2) [2/27/02 10:30:04 PM]
Important Facts About Trees
Home > How Trees Work > Important Facts
Some trees are wild, others are cloned
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
About Elm Trees
Caring for Your Elm
It's easy to think that all trees of a species are alike. This is only true, however, of
certain species. Most trees are wild-type trees, meaning that their genetic makeups are as dissimilar as individual humans. An example of a wild-type is an elm.
Other trees have been cloned to produce many trees with identical genes. This is
usually done to guarantee the presence of certain favourable characteristics of the
tree. Examples include apple and pear trees.
This distinction is important when treating diseases. In a wild-type tree, each tree
will react differently.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Some trees are ring-porous, some are diffuse-porous
Trees can be divided into ring-porous or diffuse-porous types. This refers to the
structure of the vascular system.
The vascular system of diffuse-porous
trees (such as a birch) is characterized
by vessels spread evenly throughout
the sapwood. These vessels are
produced regularly during the growing
season.
http://www.elmcare.com/trees/important_facts.htm (1 of 2) [2/27/02 10:30:07 PM]
Diffuse-Porous
Important Facts About Trees
The vessels of a ring-porous tree
(such as an elm) are generally larger
and concentrated in the outermost layer
of sapwood. These vessels are
produced early in the season.
Ring-Porous
This is significant because it affects a tree's susceptibility to vascular wilt
diseases. Ring-porous vascular systems are very efficient, but are much more
vulnerable to blockage. The elm's vulnerability to Dutch elm disease is an case in
point.
Copyright
http://www.elmcare.com/trees/important_facts.htm (2 of 2) [2/27/02 10:30:07 PM]
Structures of Trees
Home > How Trees Work > Structure of a Tree
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
Leaves
The leaves convert carbon dioxide into oxygen and provide the
tree with energy to grow and fight disease...more.
Roots
About Elm Trees
Caring for Your Elm
The roots provide structural stability to the tree and are the means by which it
takes up water and minerals...more.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Bark
Bark is the outer protective covering of tree trunks. The form and
structure of bark can differ greatly from tree to tree...more.
Copyright
http://www.elmcare.com/trees/structures/structure_of_trees.htm [2/27/02 10:30:08 PM]
How Trees Breathe
Home > How Trees Work > How Trees Breathe
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
About Elm Trees
Caring for Your Elm
Acting as an enormous "carbon sink",
trees soak up carbon dioxide from the air,
producing life-giving oxygen in return. In
fact, a medium-sized tree generates the
same amount of oxygen as each one of
us needs to breathe.
In a tree, 'breathing' takes place in the
leaf. Chlorophyll (the substance causing
the green colour) absorbs the CO2 and
uses it along with water to dissolve
minerals taken up through the roots. After the chemical reaction is completed, the
leaf releases oxygen and water vapor through its pores.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/trees/how_trees_breathe.htm [2/27/02 10:30:10 PM]
How Trees Drink
Home > How Trees Work > How Trees Drink
There are two ways that a tree can take in water: through the leaves and through
the roots.
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
Trees absorb small amounts of moisture from the air through their leaves and their
bark. Most of their water, however, comes via the roots.
Water enters the roots through thin membranes at their tips. The tree's vascular
system draws the water up through the trunk and distributes it to the leaves. The
leaves use the water to dissolve minerals. Excess water goes back to the air
through pores in the leaf - a process called transpiration.
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/trees/how_trees_drink.htm [2/27/02 10:30:12 PM]
About Elm Trees
Home > About Elms
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
The majestic elm is one of
the most beloved of all our
trees.
Dutch elm disease has
taken its toll and sadly the
elm is disappearing from
our landscape.
But through community
action, new research and a
concentrated effort, the elm
can make a comeback.
Elm Tree Diseases
Elm Tree Links
Perhaps soon, the stately elm can reclaim its rightful place in our lives.
Quick Elm Facts
Click on one of the following to learn more.
More Info...
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Copyright
http://www.elmcare.com/about_elms/about_elms.htm [2/27/02 10:30:14 PM]
The Elm Story
Home > About Elms > The Elm Story
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
The adjectives “majestic” and “stately” leap to mind when
describing elms. These trees are truly one of our most
recognizable trees whether lining our streets and
boulevards or standing on guard in a farmer's field. The
number of “Elm” streets, parks and buildings demonstrates
just how much a part of our lives these trees became.
To learn more, click on one of the topics below:
Caring for Your Elm
Elm Tree Diseases
More Info...
Elm Tree Links
The Cultivated Elm
Elms in Literature
Quick Elm Facts
Living History
Elms in Mythology
Copyright
http://www.elmcare.com/about_elms/elm_story.htm [2/27/02 10:30:16 PM]
Identifying Elms
Home > About Elms > Identifying Elms
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Elm trees make up an important part
of the North American landscape
and identifying them is the first step
in preventing their demise from
Dutch elm disease. Although there
are differences amongst the different
species of elms, this section will
focus on the American elm, which is
the most widespread.
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
To quickly identify an elm, look at the
silhouette, the leaves and the bark.
Copyright
http://www.elmcare.com/about_elms/identifying/identifying_elms.htm [2/27/02 10:30:19 PM]
Elmcare.com - Elm Species
Home > About Elms > Elm Species
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Click on one of the elm species below to
discover more.
Common Name : Scientific Name
American Elm : Ulmus americana L.
Rock Elm : Ulmus Thomasii Sarg.
Slippery Elm : Ulmus rubra Muehl.
Scotch Elm : Ulmus glabra Huds.
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Camperdown Elm : Ulmus glabra camperdownii
Siberian Elm : Ulmus pumila L.
English Elm : Ulmus procera Salisb.
Japanese Zelkova : Zelkova serrata Thunb. Mak.
Winged Elm : Ulmus alata
Chinese or Hokkaido Elm : Ulmus parvifolia
Copyright
http://www.elmcare.com/about_elms/species/elm_species.htm [2/27/02 10:30:20 PM]
Biology of Elms
Home > About Elms > Biology of Elm Trees
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
40 Million Years Old
Elm trees first made an appearance in the Miocene period, about 40 million years
ago.
Originating in central Asia, the tree has flourished and has established itself over
most of North America, Europe and Asia.
Vascular Plants
Understanding how an elm tree lives and breathes is important in understanding
how Dutch elm disease has spread.
Just like the human cardio-vascular system of arteries and veins, a tree has a
vascular system of long thin vertical tubes. This vascular system takes the water
and nutrients from the roots and distributes them throughout the tree.
Quick Elm Facts
In an elm, the cells that produce the vascular tubes are found just beneath the
bark in a layer called the cambium. After each growing season, the inner part of
the cambium dies. A new cambium is formed the next spring. If you cut through a
tree trunk, you can see the tree rings. Each ring is a cambium layer.
An elm tree has a very efficient vascular system but that also makes it vulnerable.
The same qualities that allow the elm to efficiently draw water to its upper leaves
also give fungi and insects easy access to the inner workings of the tree. The
fungus that causes Dutch elm disease, for example, essentially clogs the elm
tree’s vascular system.
Dutch elm disease can be treated. However, because the tree’s vascular system is
renewed every year, treatments have to be repeated annually.
Copyright
http://www.elmcare.com/about_elms/biology_of_elm_trees.htm [2/27/02 10:30:22 PM]
Elmcare.com - Caring for your Elm Tree
Home > Caring for Your Elm
How Trees Work
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Trees are a constant in our lives. They seem to last
forever (they certainly outlive us) and their branches
cast a protective shadow over generation after
generation.
So strong and hardy are trees that we often assume
that they endure just about any hardship without any
help from us.
But trees outside their natural setting are often under
tremendous stress.
And yes, there is much we can do to help them.
Fertilizing; pruning; giving the tree room to grow and breathe. We can help our
trees to thrive and ensure that they can continue to give pleasure for generations
to come.
Click on one of the following for more information:
Fertilizing
Watering
Pruning
Obstacles to Growth
Lawn Care
Disposal of Dead Elms
Copyright
http://www.elmcare.com/caring/caring_for_your_elm.htm [2/27/02 10:30:24 PM]
Elmcare.com - Fertilizing
Home > Caring for your Elm > Fertilizing
How Trees Work
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elms should be fertilized once or twice a year. However, not just any fertilizer will
do and using the wrong type of fertilizer can actually increase the chances that
your tree will contract Dutch elm disease. Avoid standard "one-size-fits-all" lawn
and turf fertilizer. In particular, fertilizers that release large amounts of Nitrogen
quickly into the soil can encourage structurally weak growth that could attract the
elm bark beetles carrying the Dutch elm disease fungus. Aside from the
formulation, the method of fertilization differs from that of your grass. In order to
give your trees the most benefit, the fertilizer must be placed below the grass
roots.
To find out how to obtain fertilizer specially selected for use on elm trees, click
here.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/caring/fertilizing.htm [2/27/02 10:30:26 PM]
Elmcare.com - Pruning Elm Trees
Home > Caring for your Elm > Pruning
Pruning is one of the most important ways we can help our trees.
How Trees Work
Regular removal of dead branches:
About Elm Trees
●
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
●
●
●
decreases the breeding area for disease-carrying insects
promotes growth
removes safety hazards
improve the tree’s appearance.
Take care! Improper or untimely pruning can do more harm than good.
Click on a topic to learn more:
Elm Tree Diseases
Elm Tree Links
Why Prune?
Timing
Quick Elm Facts
Types of Pruning
Pruning Pitfalls
Technique
Copyright
http://www.elmcare.com/caring/pruning/pruning.htm [2/27/02 10:30:27 PM]
Elmcare.com - Lawn Care
Home > Caring for your Elm > Lawn Care
Grass and trees are not always the best of friends.
How Trees Work
About Elm Trees
Caring for Your
In natural settings, the ground around large shade trees is covered with leaves. As
the leaves decompose, they release nutrients which the tree needs. Not so in our
cities where are trees are surrounded by grass. The grass actually competes with
the tree for water and nutrients.
Elm Tree
How you care for your lawn can affect the health of your elm tree.
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Elm Tree Links
Fertilizing
Scatter fertilizer around a tree and you will end up with very healthy grass. Tree
food stakes inserted into the ground release nutrients below the grass layer. Use
fertilizers specifically designed for shade or elm trees.
Quick Elm Facts
Mowing
Take care when mowing. Lawn mowers can damage a tree. Better yet, avoid the
problem by keeping the grass back from the base of the tree. A buffer zone of
loose soil or mulch is ideal.
Copyright
http://www.elmcare.com/caring/lawn_care.htm [2/27/02 10:30:29 PM]
Elmcare.com - Watering Elm Trees
Home > Caring for your Elm > Watering
How Trees Work
Water is, of course, vital to the survival and health of a tree. You can provide a
tree with the moisture it needs.
About Elm Trees
Caring for Your
Elm Tree
How
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
A tree takes moisture in through its root system. At the tip of the root, there are
tiny structures called root hairs which absorb moisture from the surrounding soil.
This is where you want to target your watering.
Elm Tree Diseases
In an elm, the tips of the roots are usually located outside of the weeping or drip
line. This is the outermost extent of the crown of the tree. Therefore, sprinkling
water onto the trunk will have little or adverse effect on the tree's health.
Elm Tree Links
Quick Elm Facts
It is important to remember that grass and other vegetation compete with a tree for
moisture. As a result, sprinkling is not a very efficient method of watering. Firstly,
there is extensive evaporation, and secondly the grass absorbs a large percentage
of this water.
A preferable method of watering is to soak the ground outside the weeping line
with a hose. There are also special devices that allow you to apply moisture
directly into the ground near the roots.
It is important to allow the soil to dry in between waterings. If the soil is constantly
wet, it can easily become compacted, hindering gas exchange with the air.
When
Often nature provides all the moisture a tree needs. It is times of drought or in
certain urban environments when watering is required.
●
Examine the leaves: wilting, browning, discoloured margins - these are all
signs your tree needs moisture
http://www.elmcare.com/caring/watering.htm (1 of 2) [2/27/02 10:30:31 PM]
Elmcare.com - Watering Elm Trees
●
●
Examine the grass: if your lawn is yellowing, there is good chance that
your tree lacks moisture even if it has yet to show signs.
Examine nearby trees: If other trees in your area show signs of drought,
your tree may be next. Often other species, such as maples, show signs
earlier than elms giving an early warning signal.
Copyright
http://www.elmcare.com/caring/watering.htm (2 of 2) [2/27/02 10:30:31 PM]
Elmcare.com - Obstacles to Growth
Home > Caring for your Elm > Obstacles to Growth
How Trees Work
Sidewalks, utility lines, houses, poor soil, polluted air - it is a wonder that our trees
do as well as they do. We can help our trees thrive and grow by managing some of
the obstacles they face.
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Elm Tree Links
Physical Obstacles
Due to the sheer size of a mature elm, things tend to get in its way. The easiest
way to avoid conflicts with physical obstacles is to plan around them. This means
care when planting.
A young tree always looks lonely in a garden. But that spindly litle tree will
eventually grow to be more than 30 metres tall with a crown that will engulf
everything nearby. Elm trees should be planted at least 5 metres (15 feet) away
from houses.
Quick Elm Facts
Never plant an American Elm under utility lines. The result will be frequent and
costly pruning.
Construction
When doing construction around an elm tree, care must be taken to avoid cutting
the root system.
It is difficult for the tree to close root wounds. Cutting roots can leave the tree
vulnerable to attack by a fungal disease such as Dutch Elm Disease.
If cutting the root is unavoidable, attempt to make clean cuts exposing as little
surface area as possible.
http://www.elmcare.com/caring/obstacles.htm (1 of 2) [2/27/02 10:30:32 PM]
Elmcare.com - Obstacles to Growth
Copyright
http://www.elmcare.com/caring/obstacles.htm (2 of 2) [2/27/02 10:30:32 PM]
Elmcare.com - Disposal of Dead Elms
Home > Caring for your Elm > Disposal of Dead Elms
How Trees Work
A dead elm tree is a threat
to all the other elm trees in
the neighbourhood.
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Because dead wood is an
ideal breeding ground for
the elm bark beetle and
the DED fungus, disposal
of dead limbs and trees
must be done properly and
quickly.
If you have a dead elm,
first remove the major limbs and proceed to cut down the tree.
Remember taking trees down is not a job for the amateur. Call a tree removal
company. Some municipalities offer disposal services for large trees.
Wood should be burned immediately. It should not be stored. Some communities
have strict by-laws prohibiting the storage and transportation of elm firewood.
If there is insufficient space for burning, the wood can be buried.
Copyright
http://www.elmcare.com/caring/disposal_of_dead_elms.htm [2/27/02 10:30:35 PM]
Elmcare.com - Elm Tree Diseases
Home > Elm Tree Diseases
While elm trees are extremely hardy, they are still
susceptible to attack from diseases or insects.
How Trees Work
About Elm Trees
If your elm tree seems unhealthy, it could be suffering
from one of the diseases on the left.
Caring for Your Elm
Elm Tree
Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Asian Longhorned Beetle
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/disease/elm_diseases.htm [2/27/02 10:30:36 PM]
Elmcare.com - Dutch Elm Disease
Home > Elm Tree Diseases > Dutch Elm Disease
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Dutch Elm Disease
History
Transmission Symptoms
Prevention
Treatments
New Research
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Quick Elm Facts
Dutch elm disease (DED) is the most devastating
shade tree disease in North America. It is a wilt
disease with an extremely high fatality rate among
elms.
How Dutch Elm Disease Kills
Dutch elm disease (or DED) is caused by a fungus.
After the disease is contracted, spores rapidly reproduce and spread toxins
throughout the tree.
The fungus blocks the water-conducting or vascular system of the tree preventing
water and minerals from reaching the branches and leaves. The leaves wilt and
eventually the tree dies.
The Fungus
The fungus Ophiostoma (Ceratocystis) ulmi attacks various species of elm. It can
kill a tree within a few weeks or it can kill it gradually over a period of years.
There are two strains of the fungus in North America - the non-aggressive strain
(O. ulmi) and the aggressive strain (O. novo-ulmi). While the elm’s natural
defense mechanism tries to fight off the fungus, the aggressive strain often moves
too quickly for the tree to react without human intervention.
How Long Does It Take for the Fungus to Destroy a Tree?
That depends on the age and health of the tree. A younger fast-growing tree can
die quickly. Some younger trees have some natural resistance to DED. However,
this resistance tends to wear off after 15-20 years. Slow growing older trees can
linger for a year or two.
Is There a Cure for DED?
When an elm tree detects the presence of the fungus, it produces a number of
defensive compounds. ‘Mansonones’, for example, are toxic to the DED fungus.
However, left to its own devices, a tree cannot produce enough to fight off the
disease.
Researchers are now learning how to stimulate the tree’s natural defenses to
produce larger quantities of mansonones. It is a promising breakthrough. For
more information on the new DED treatment, click here.
http://www.elmcare.com/disease/dutchelm/dutch_elm_disease.htm (1 of 2) [2/27/02 10:30:39 PM]
Elmcare.com - Dutch Elm Disease
For more information on Dutch elm disease, click on one of the topics below:
History of Dutch elm disease
Prevention of Dutch elm disease
Transmission of Dutch elm disease
Traditional Treatments
Symptoms of Dutch elm disease
Innovative Treatment
Thank you for visiting elmcare.com
Site Map | Contact Us | About this site | Suggestions | Home
www.elmguard.com | www.arborscience.com
Contact the Webmaster | Copyright
ArborScience Inc.
270 Yorkland Blvd. Toronto, ON, Canada M2J 5C9
Ph: (416) 491-1436 Fax: (416) 491-5343
Copyright
http://www.elmcare.com/disease/dutchelm/dutch_elm_disease.htm (2 of 2) [2/27/02 10:30:39 PM]
History of Dutch Elm Disease
Home > Elm Tree Diseases > Dutch Elm Disease > History
How Trees Work
About Elm Trees
Caring for Your Elm
Why “Dutch” elm disease?
The Dutch may have been unfairly blamed for the loss
of millions of trees. “Dutch” elm disease got its name
because Dutch scientists identified it when the
disease made an appearance in Holland in 1917.
From there, it spread quickly wiping out many of the
European elms.
Elm Tree Diseases
Dutch Elm Disease
History of DED
Prevention
Treatments
New Research
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Quick Elm Facts
Origins
Scientists believe that the fungus that causes DED originally came from the
Himalayas. It travelled to Europe from the Dutch East Indies in the late 1800’s. In
the 1930’s, the disease spread to North America on wooden crates made with
infected elm wood.
A second introduction of the disease in North America occurred in 1945 starting in
Sorel, Quebec. It destroyed over half the remaining elm trees in eastern Canada
and the US. By 1976, only 34 million elm trees were left.
New strains of the disease appeared in the 1960’s in England. Within 20 years, 17
million of the country’s 23 million elm trees were dead.
Moving West
The disease has now spread to Manitoba and Saskatchewan where there are
approximately 500,000 elm trees in the cities. Three to five percent of the elms die
each year
Winnipeg is spending C$2.5 million a year on sanitation and pruning. Having lost
40,000 trees in the last 20 years, the city’s elm population is now just 200,000.
More Than Just Beauty
Mature trees add to property values. The estimated value of a mature elm for
insurance purposes is C$3,600 (US$2,500) per tree. With roughly 650,000 elms in
cities in Canada, the elms are worth C$2.3 billion. The 7 million urban trees in the
US are worth US$17.5 billion.
Source: "The American elm and Dutch elm disease" M. Hubbes, Forestry Chronicle, March/April
1999. Vol. 75, No. 2, p.265
http://www.elmcare.com/disease/dutchelm/history_of_dutch_elm_disease.htm (1 of 2) [2/27/02 10:30:41 PM]
History of Dutch Elm Disease
Copyright
http://www.elmcare.com/disease/dutchelm/history_of_dutch_elm_disease.htm (2 of 2) [2/27/02 10:30:41 PM]
Transmission of Dutch Elm Disease
Home > Elm Tree Diseases > Dutch Elm Disease > Transmission
How Trees Work
Dutch elm disease can be transmitted from tree to tree by the elm bark beetle, root
grafts and infected tools.
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Bark Beetle
Dutch Elm Disease
History of DED
Transmission
Symptoms
Prevention
Treatments
New Research
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
The elm bark beetle (not to be
confused with the Elm Leaf
Beetle) is by far the most
important factor in Dutch Elm
Disease.
These tiny insects’ lives revolve
around elm trees. The female
beetle tunnels into the tree
between the bark and the wood
and lays its eggs. When the eggs
hatch, the larvae tunnel further into the tree in order to feed before emerging as
mature beetles.
Adults feed in the crown of the tree, moving from tree to tree before breeding
again.
Quick Elm Facts
If a beetle breeds or feeds in a DED-infected tree, the sticky spores of the fungus
become attached to its back. When the beetle moves to a healthy tree, so too do
the spores.
There are two species of the elm bark beetle in North America – the European and
the Native elm bark beetles. The European is more temperature sensitive and
lives mainly in southern regions. The Native is dominant in the mid-west.
http://www.elmcare.com/disease/dutchelm/transmission.htm (1 of 3) [2/27/02 10:30:44 PM]
Brood Gallery of Native Bark Beetle
Brood Gallery of European Bark Beetle
The native elm bark beetle consists of two separate breeding groups. One group
overwinters as larvae in the breeding tunnels, while the second group overwinters
as adults. These adults emerge from mid-April to mid-May. It is their feeding
phase that causes the majority of DED infections. It is believed that the European
elm bark beetle overwinters as larvae.
Much of the effort to control the spread of DED has focused on controlling the
beetle population with insecticides or trapping. These methods have enjoyed some
degree of success but the beetles remain the single most important factor in the
spread of the disease.
Top
Root Grafts
Mature elms have a large system of roots. When these roots come into contact
with those of another elm, they can graft together to promote the exchange of
nutrients. The fungus can spread through the root grafts, infecting the
neighbouring trees.
A tree infected by root graft transmission shows very sudden and devastating
symptoms. Treatment is much less effective.
Top
Infected Tools
Pruning tools can also transmit Dutch elm disease. All tools should be cleaned
before pruning a healthy tree. Some arborists recommend a 10% solution of
household bleach.
Top
Copyright
Symptoms of Dutch Elm Disease
Home > Elm Tree Diseases > Dutch Elm Disease > Symptoms
An infected elm tree usually exhibits symptoms soon after infection. Because of
the speed with which the disease attacks, detecting symptoms as early as possible
is essential for treatment.
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The first sign of the disease is the sudden
wilting of leaves in the upper reaches of the
tree
Dutch Elm Disease
History
Transmission
Prevention
Symptoms
Treatments
New Research
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Next, the leaves change colour from green
to yellow to brown. They then shrivel and
die.
Timing
Quick Elm Facts
If the infection occurs very late in the season, the leaves will appear to fall
normally. However, the following spring the new leaves will be smaller than
normal. The tree will often die before mid-summer.
In late summer, it may be difficult to distinguish between wilting and natural fall
colours.
Bark Signs
http://www.elmcare.com/disease/dutchelm/symptoms_of_dutch_elm_disease.htm (1 of 2) [2/27/02 10:30:46 PM]
Symptoms of Dutch Elm Disease
Discolouration of the wood is also a sign of
the disease. If you peel back the bark on a
wilted branch, you will see some streaking
on the wood.
Copyright
http://www.elmcare.com/disease/dutchelm/symptoms_of_dutch_elm_disease.htm (2 of 2) [2/27/02 10:30:46 PM]
Prevention of Dutch Elm Disease
Home > Elm Tree Diseases > Dutch Elm Disease > Prevention
Integrated Sanitation Program
How Trees Work
About Elm Trees
Caring for Your Elm
Traditionally, people have tried to control Dutch Elm Disease by stopping it from
spreading. Many communities, like the City of Winnipeg, have adopted a highly coordinated program to try to save their elms.
Elm Tree Diseases
Dutch Elm Disease
History
Prevention
Treatments
New Research
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Quick Elm Facts
Surveillance
Detection is the first step. The earlier the disease can be caught, the quicker it can
be stopped.
Some communities and government agencies have designated experts to help
make a definitive diagnosis. Contact these experts at the first suspicion of DED.
Early detection can help prevent infection of nearby trees.
Disposal
Dead wood is an ideal breeding ground for the elm bark beetle. Dead wood must
be properly removed and destroyed.
Firewood spreads the disease. Storing elm firewood is illegal in many jurisdictions
with active DED control programs.
All elm wood should be buried, burned or chipped immediately.
Pruning
Pruning promotes tree health. Regular pruning helps a tree use its natural
defenses against DED. It also removes breeding sites for the elm bark beetle.
Click here for proper maintenance pruning techniques.
http://www.elmcare.com/disease/dutchelm/integrated_sanitation_program.htm (1 of 3) [2/27/02 10:30:49 PM]
An elm in downtown Toronto is pruned in winter to discourage further spread of DED
When you prune is as important as how you prune. Pruning creates open cuts in a
tree’s bark that take time to heal. Since the elm bark beetle is attracted to these
wounds, pruning should not take place from early April to late July when the beetle
is active.
Some municipalities have by-laws stating when pruning can be legally done.
Insecticides
Chemical insecticides are used to control the elm bark beetle.
Chemicals are sprayed on the crown, bark and base of the tree in early April when
the beetles become active. The chemicals kill the emerging adult beetles before
they can introduce the fungus by feeding on the tree. Insecticides include
Methoxychlor, carbaryl (Sevin) and chlorpyrifos (Dursban).
Some cities spray all boulevard and park elms. They may also offer their services
to individual homeowners.
Before using any chemicals, consult a professional arborist. Most insecticides can
be harmful to people, pets and the environment.
Insecticides are used less than they were in the past because proper dead wood
disposal is more effective.
Fungicides
Fungicides can help guard against Dutch elm disease.
Chemicals such as Arbotect 20-s, Alamo, and Lignasan, are injected into the tree
through holes drilled in the base or in the root-flares.
Fungicide injection is both a preventative measure and a treatment for infected
elms. However, fungicide injections are best left to professional arborists.
Preventative injections can actually have an adverse affect on a tree’s health
making it more susceptible to DED infection.
Fungicide injection should never be used as a substitute for pruning and other
measures.
Natural Resistance
A team from the University of Toronto has recently developed an innovative
approach to preventing Dutch elm disease.
An “elicitor” inserted into the tree stimulates the tree’s natural defense mechanism
which in turn prevents the fungus from gaining a foothold in the tree’s vascular
system.
For long term protection, the elicitor must be applied on an annual basis. Along
with regular pruning, it is an extremely effective method to prevent DED. It is also
completely safe because it uses the tree’s natural defenses.
For more information about the elicitor, click here.
Top
Copyright
Traditional Treatments of Dutch Elm Disease
Home > Elm Tree Diseases > Dutch Elm Disease > Traditional Treatments
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Dutch Elm Disease
History
Prevention
Treatments
New Research
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Quick Elm Facts
Pruning
Pruning is an extremely effective way to treat a tree infected with DED.
Timely removal of diseased wood checks the spread of the disease. It is however
less effective for well-established infections or for root-graft infections.
When you prune is extremely important. Pruning opens fresh wounds in the tree
that take time to heal. The elm bark beetles are attracted to these wounds.
Pruning should not take place while the beetles are active (from early April to late
July). Some municipalities have by-laws defining when you are legally permitted
to prune elm trees.
Technique
●
●
●
●
On an infected tree, locate the wilted branch and remove the bark until
sapwood can be found with no discoloration.
Cut the branch approximately 10 feet below the discolored area. The
farther below the discolored area the limb is cut, the greater the chance of
freeing the elm of the disease.
Properly dispose of dead wood.
Disinfect tools using a 10% household bleach solution.
The loss of a major limb is regrettable but it can prevent the loss of the tree. One
study reported that 60% of the trees that had been pruned at the early signs of the
disease survived.
If the symptoms are allowed to continue, however, the success rate plummets.
Studies have shown that if less than 5% of a tree is infected, pruning successful
stops the disease 65% of the time. If 20% of the tree is infected, the success rate
drops to 0%. 1
Chemical Fungicides
Treating elm trees with systemic fungicides is a popular way to combat the effects
of Dutch elm disease. Chemicals are injected into the tree either through holes
drilled in the base of the tree or in the root-flares. Some chemicals that are
currently used include Arbotect 20-s, Alamo and Lignasan.
http://www.elmcare.com/disease/dutchelm/traditional_treatments.htm (1 of 2) [2/27/02 10:30:50 PM]
Traditional Treatments of Dutch Elm Disease
Chemical fungicides can be effective for trees in the early stages of the disease. If,
however, a tree has advanced DED or has contracted the disease through a root
graft, fungicides have little or no effect.
Fungicides are not a substitute for pruning and other measures.
Due to the difficulty of the procedure, fungicide injections are best left to
professional arborists. A preventative injection into a healthy tree can adversely
affect its health making it more susceptible to a DED infection.
1 (Himlick and Ceplecha, 1976)
Copyright
http://www.elmcare.com/disease/dutchelm/traditional_treatments.htm (2 of 2) [2/27/02 10:30:50 PM]
Innovative Treatment for Dutch Elm Disease
Home > Elm Tree Diseases > Dutch Elm Disease > Innovative New Treatment
Jump ahead to:
Unique Discovery
How It Is Applied
How It Works
Using ELMguard
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Dutch Elm Disease
History
Prevention
Treatments
New Research
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
The elicitor in pellet form being inserted into a young elm.
Over the past twenty years, a team of scientists from the University of Toronto,
Faculty of Forestry, under the leadership of Dr. Martin Hubbes, has been working
on an exciting, new all-natural treatment for the prevention of Dutch elm disease.
The new treatment or "elicitor" does not work directly on the fungus causing Dutch
elm disease. Instead, it stimulates the tree's own immune system. The treatment
has a strong protective effect because it activates the tree's natural defense
response to Dutch elm disease.
Elm Tree Links
Quick Elm Facts
Unique Discovery
The treatment is based on a special natural protein which was
discovered by the University of Toronto scientific team as a
result of intensive advanced molecular biology research. The
protein elicits a defensive response in the tree which enables
it to resist the onset of the aggressive and deadly strain of
Dutch elm disease. The treatment is unique because it is all natural - it contains
no synthetic chemicals and is non-toxic.
Top
http://www.elmcare.com/disease/dutchelm/innovative_new_treatment.htm (1 of 3) [2/27/02 10:30:53 PM]
How It Is Applied
ELMguard is an annual treatment applied to the tree in the spring. It is injected
directly into the tree in either a liquid or pellet form through small holes drilled in
the tree's outer growth ring. After injecting ELMguard, a wax sealer is used to
close the small holes. During the season, the tree then closes the hole naturally
with new wood growth.
Top
How It Works
After the injection, the tree's vascular system absorbs the protein starting a series
of defensive reactions.
These reactions include the production of mansonones and cell lignification
(hardening). Mansonones are a naturally produced substance and play an
important role in an elm tree's defense response against Dutch elm and other
diseases.
Top
Using ELMguard
ELMguard should be used as part of a comprehensive elm care program which
promotes good health, proper sanitation (pruning) and the use of the elicitor to
boost the tree's immune response system.
ELMguard does not provide 100% protection against Dutch elm disease in all elm
trees because of the simple fact that each elm is different. Just as each of us is
genetically different from everyone else, the same is true for wild elms. Therefore,
each tree will react slightly differently to the treatment. Also, general health of an
individual tree is a major factor in determining ELMguard's effectiveness.
For further information on ELMguard and other natural treatments for the control
and prevention of Dutch elm disease, visit www.elmguard.com.
Top
Copyright
Elmcare.com - Elm Leaf Beetle
Home > Elm Tree Diseases > Elm Leaf Beetle
The elm leaf beetle is a pest which poses some danger to the elm tree.
How Trees Work
About Elm Trees
Caring for Your Elm
Adult beetles are approximately ¼ inch
long. Their colour fades from yellow to olive
as they mature. They have black stripes on
the wing covers and four black spots on the
thorax. The larvae are about 1/2 inch long
and a dull yellow colour.
Elm Tree Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
The adults lay eggs on
the underside of elm
leaves in late May and early June. After they hatch, the larvae
begin feeding on the flesh of the leaf, leaving only the veins
intact. About three weeks later, the adults emerge and chew
small holes in the leaves.
A tree can survive an infestation of elm leaf beetles. However, its weakened state
will make it more susceptible to other diseases such as Dutch elm disease.
Birds, toads and other insects are natural enemies of the elm leaf beetle. There
are also a number of effective pesticides.
Quick Elm Facts
As many chemical pesticides can be poisonous, care should be taken to read the
label before use.
Copyright
http://www.elmcare.com/disease/elm_leaf_beetle.htm [2/27/02 10:30:55 PM]
Elmcare.com - Verticillium Wilt
Home > Elm Tree Diseases > Verticillium Wilt
Verticillium wilt is caused by a fungus that lives in the soil. The fungus penetrates
the root system of susceptible plants, eventually blocking the plant’s waterconducting system.
How Trees Work
About Elm Trees
Caring for Your Elm
The fungus affects more than 300 types of plants throughout the world - from
raspberries and tomatoes, to maples and elms. Although the disease occurs in
naturally forested areas, it is found mostly in landscape plantings.
Elm Tree Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Quick Elm Facts
How It Spreads
The two fungal species, V. alboatrum and V. dahliae, can survive in the soil for
decades lying in wait for new plants to move in. The fungus usually enters the
roots through wounds, but if the tree is weak, it can actually penetrate the root.
When a plant dies, the fungus enters a resting state, producing structures called
“microsclerotia”. These structures can be easily transported from place to place
when trees are transplanted. In dry conditions, these microsclerotia can by carried
by the wind to infect new areas.
Tools can also carry the fungus, so proper sanitation procedures should be
followed.
How the Fungus Kills
Once inside the root, the fungus reproduces and spreads through the tree via the
xylem, or water-conducting tissue. As it spreads, it causes tissue damage and
clogs the xylem, preventing water from reaching the outer branches. Without
moisture and necessary nutrients, these outer limbs wilt and die.
Symptoms
The first sign of disease is a slight yellowing of the foliage (similar to symptoms of
http://www.elmcare.com/disease/verticillium_wilt.htm (1 of 2) [2/27/02 10:30:57 PM]
Elmcare.com - Verticillium Wilt
Dutch elm disease although with less extensive crown involvement). There is also
discolouration of the wood. Branches, stems and roots show a light to dark brown
staining of the sapwood. Cankers may form on the branch and stem.
Trees with extensive infection show reduced growth rates and branch dieback.
Younger trees usually succumb within one year. Older trees tend to deteriorate for
a few years before finally dying.
Control
Fertilizing
Fertilizing with a balanced mixture light on nitrogen (5-10-10) may help to alleviate
some of the symptoms. High nitrogen fertilizers, however, should be avoided.
They promote new growth that would be vulnerable to the fungus.
Natural Defenses
One area that does offer hope comes from the Forestry Department of the
University of Toronto. A team led by Dr. Martin Hubbes has isolated a
glycoprotein that can potentially boost the natural defenses of a tree. Although
research so far has focused on Dutch elm disease, stimulation of natural defenses
could also be effective with Verticillium wilt.
Copyright
http://www.elmcare.com/disease/verticillium_wilt.htm (2 of 2) [2/27/02 10:30:57 PM]
Elmcare.com - Elm Yellows
Home > Elm Tree Diseases > Elm Yellows
How Trees Work
Also known as Elm Phloem Necrosis, this
disease infects trees native to North
America, while European and Asian elms
seem to be immune.
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Quick Elm Facts
The first symptom is the death of root hairs
and tips followed by foliar wilt. Leaves will
turn yellow, then brown and curl up.
Generally the tree dies a few weeks after
foliar symptoms manifest themselves.
Other symptoms include yellowing of the sapwood and a wintergreen odour
emanating form the bark. The causal agent of elm yellows is a “mycoplasma-like
organism” (MLO) which is classified between a virus and a bacterium. This
organism is carried from tree to tree by leafhoppers. There is no known effective
treatment for elm yellows, so disposal of infected trees is the only option. The
most effective preventative measure is controlling the leafhopper population.
In order to do this, a homeowner can utilize a pesticide such as methoxychlor
emulsifiable concentrate. Applied during the bud breaks, this chemical represents
an effective control of the leafhopper. As most chemical pesticides are poisonous,
care should be taken to read the label before use.
Copyright
http://www.elmcare.com/disease/elm_yellows.htm [2/27/02 10:30:59 PM]
Elmcare.com - Cankers
Home > Elm Tree Diseases > Cankers
Cankers are a fungal disease.
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The leaves turn bright yellow (similar to the
symptoms of Dutch elm disease) with
reddish-brown to black cankers on the twigs
and small branches. The infected leaves
can stay on the tree for several weeks.
There is no chemical treatment. Pruning is
the best way to manage this disease.
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/disease/cankers.htm [2/27/02 10:31:01 PM]
Elmcare.com - Wetwood
Home > Elm Tree Diseases > Wetwood
How Trees Work
About Elm Trees
Caring for Your Elm
Wetwood is caused by a bacterial infection and is very
common in elms and many other species. The infection
causes moisture to be retained in the wood and also
produces metabolic gases that increase the internal
pressures in the tree. Periodically the liquid will be forced out
of the tree through wound sites. The liquid oozes out and
down the tree, where other organisms colonize it. This liquid
is called slime flux and is known to have a foul odour.
Elm Tree Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Elm Tree Links
Wetwood becomes a problem only when enough infection
sites occur on the tree to compromise its structural integrity. A
professional or consulting arborist should judge this.
Otherwise, wetwood can be viewed as somewhat beneficial,
as the moist environment that it creates in the tree helps to
prevent decay fungi from colonizing the tree. Symptoms
appear as long discoloured streaks on the trunk. Leaves may
also exhibit some scorch if the infection is extensive.
At present, there is no treatment for wetwood.
Quick Elm Facts
Copyright
http://www.elmcare.com/disease/wetwood_or_slime_flux.htm [2/27/02 10:31:03 PM]
http://www.elmcare.com/disease/elm_leaf_black_spot.htm
Home > Elm Tree Diseases > Elm Leaf Black Spot
Elm Leaf Black Spot, also called elm
anthracnose, is another fungal disease
affecting the leaves of an elm tree.
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
First, yellow spots appear on the
topside of the leaves. These spots are
followed by slightly raised black fruiting
bodies.
Removing diseased leaves can aid in
treatment.
Nurseries use chemicals such as
Bordeaux and mancozeb but these are
not recommended for home use.
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/disease/elm_leaf_black_spot.htm [2/27/02 10:31:06 PM]
http://www.elmcare.com/disease/elm_leaf_miner.htm
Home > Elm Tree Diseases > Elm Leaf Miner
The elm leaf miner is a common pest throughout eastern North America.
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
This insect feeds inside the leaf. The larvae tunnel through the leaf forming
blotches and discolouration. As the miners move to the outer edge of the leaf, the
leaf turns brown. The larvae finish feeding in late June or early July and then fall to
the ground where they pupate.
Whitish with pale brown heads, the elf leaf miner larvae measure about 6mm in
length. They overwinter in the soil and produces a brown papery cocoon. In the
spring, they emerges as an adult sawfly.
Pesticides can control the spread of the elm leaf miner. Injected into the trunk after
the leaves are fully formed, the pesticide will repel the larvae for about 2 months.
As many chemical pesticides can be poisonous, care should be taken to read the
label before use.
Natural predators can also help. Ground beetles, braconid wasps and
ichneumonids all prey on the leaf miner during various stages of development. To
attract these predators, introduce plant species such as evening primrose,
evergreen eunymous, baltic, boston or english ivy, fennel or rue.
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/disease/elm_leaf_miner.htm [2/27/02 10:31:07 PM]
Elmcare.com - Asian Longhorned Beetle
Home > Elm Tree Diseases > Asian Longhorned Beetle
See also www.asian-longhorned-beetle.com.
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Dutch Elm Disease
Elm Leaf Beetle
Verticillium Wilt
Elm Yellows
Cankers
Wetwood
Elm Leaf Black Spot
Elm Leaf Miner
Asian Longhorned
Beetle
A wood-chewing insect from China is the newest threat to North America's elms.
Slightly larger than a cockroach, the Asian longhorned beetle chews its way into
the trunks of the trees where it lays its eggs. Eventually, the tree dies.
Although elms will be affected, the primary target of this insect are maples. Loss
of maple trees could have a considerable impact on the maple syrup industry.
Carried over from China in wooden skids, the beetle has made its presence felt in
Chicago. Officials have begun extensive efforts to control further spread.
Source: Globe and Mail August 18, 1999
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/disease/asian_longhorned_beetle.htm [2/27/02 10:31:09 PM]
Elmcare.com - The Elm Community
Home > Elm Tree Links
Canada
United States
International
Other Information Links
Elms in the Media
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Canada
Manitoba
●
Quick Elm Facts
●
Winnipeg's Coalition to Save the Elms
Manitoba Natural Resources
Forest Landscape Management, Forestry Branch
Nova Scotia
●
●
Nova Scotia Provincial Regulation Registry
Halifax Regional Municipality, City of Dartmouth
Bylaw
Ontario
●
Ontario Shade Tree Council
Saskatchewan
●
●
●
Saskatchewan Environment and Resource
Management
CETAC-WEST
College of Agriculture, University of Saskatchewan
http://www.elmcare.com/community/elmcommunity.htm (1 of 4) [2/27/02 10:31:11 PM]
United States
National
●
Department of the Interior, National Parks Service,
Integrated Pest Management Dutch Elm Disease
Manual
Colorado
●
Colorado State University Cooperative Extension
Plant Talk
Illinois
●
●
Morton Arboretum in Chicago "A Brief History of
Dutch Elm Disease"
Des Plaines City Services
Iowa
●
Iowa State University Horticulture and Home Pest
News
Kansas
●
Kansas State University Research and Extension
Kentucky
●
Kentucky State University Extension Service
Michigan
●
Michigan State University Extension Service
Minnesota
●
University of Minnesota Center for Urban Ecology
and Sustainability
Missouri
●
University of Missouri-Columbia Extension
Montana
●
Montana State University Extension Service
North Dakota
●
North Dakota State University Extension Service
Washington
●
International
Washington State University Cooperative Extension,
Western Washington
International Links coming soon
Other Information
Links
●
Elms Return to Elm Street
Elms in the Media
●
Smithsonian Magazine "Racing to Revive our
Embattled Elms", June 1998.
If you feel a link should be included here, please contact us.
Also, if you live in an area not listed above, we can do some research for you to
see if we can find some helpful resources.
Copyright
Quick Facts
Home > Quick Facts
●
Trees add not only beauty but value to our property.
The value of a mature elm for insurance purposes is
US$2,500 (C$3,600).
●
The 7,700,000 elm trees in urban centres in North
America have a combined value of over US$19 billion
●
Dutch elm disease got its name because it was discovered by scientists
in Holland in 1917.
●
The seven Dutch scientists who first identified Dutch elm disease were
all women.
●
Dutch elm disease hit England in the 1960’s and within 20 years had
killed 17 million of the country’s 23 million elm trees.
●
A second out-break of Dutch elm disease in 1945, destroyed secondgeneration elms in Eastern Canada and the United States. The elm
population dropped from 77 million to 34 million by 1976.
●
Fully mature elm trees can live as long as 300 years.
●
The cooling effect of one urban elm tree is equivalent to five air
conditioning units.
●
North American settlers named the elm “the lady of the forest”.
●
Elm trees first appeared in the Miocene period, about 40 million years
ago.
●
The American Elm grows to over 115 feet tall and can have a diameter
in excess of ten feet.
●
The Iroquois used elm bark to make canoes, rope and utensils
●
The film “Nightmare on Elm Street” has absolutely nothing to do with
elm trees
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
http://www.elmcare.com/quick_facts.htm (1 of 2) [2/27/02 10:31:12 PM]
Quick Facts
Copyright
http://www.elmcare.com/quick_facts.htm (2 of 2) [2/27/02 10:31:12 PM]
Site Map
Home > Site Map
Caring for your Elm
About This Site
Quick Elm Facts
Fertilizing
How Trees Work
Pruning
Important Facts
Types of Trees
How Trees Breathe
How Trees Drink
Structures of Trees
Leaves
Roots
Bark
About Elms
Why Prune?
Types of Pruning
Proper Technique
Timing of Pruning
Pruning Pitfalls
Lawn Care
Obstacles to Growth
Disposal of Dead Elms
Elms Tree Diseases
Identifying Elms
Silhouette
Leaves
Bark
Elm Species
The Elm Story
Elms
Elms
Elms
Elms
and Humans
in History
in Literature
in Mythology
Biology of Elms
The Elm Community
Elm Research
Elm Community Groups and Links
Copyright
http://www.elmcare.com/sitemap.htm (1 of 2) [2/27/02 10:31:14 PM]
Dutch elm disease
History of DED
Symptoms of DED
Transmission of DED
Preventing DED
Treatments
New Research
Asian Longhorned beetle
Cankers
Elm Leaf Beetle
Elm Leaf Black Spot
Elm Leaf Miner
Elm Yellows
Verticillium Wilt
Wetwood
Ask the Experts
Past Questions and Answers
Site Map
Copyright
http://www.elmcare.com/sitemap.htm (2 of 2) [2/27/02 10:31:14 PM]
About elmcare.com
Home > About This Site
Dutch elm disease
This site is designed to be a comprehensive resource for homeowners,
researchers and tree care professionals to find information about about elm trees.
About Elmcare
How Trees Work
About Elm Trees
Caring for Your Elm
●
Quick Facts
●
●
How to Care for Your Tree
The Elmcare Newsletter - Sign up on the Homepage!
●
Dutch Elm Disease
●
The Elm's Place In History
●
Links to elm tree resources
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
....and much more!
Awards for Elmcare.com
http://www.elmcare.com/about_this_site.htm (1 of 2) [2/27/02 10:31:16 PM]
About elmcare.com
Copyright
http://www.elmcare.com/about_this_site.htm (2 of 2) [2/27/02 10:31:16 PM]
Copyright
Home > Copyright
This site is copyrighted by ArborScience. While we would be happy to share any
of our information, we do require a written request.
How Trees Work
About Elm Trees
Caring for Your Elm
Please note that while we have taken every effort to make sure that this site
contains accurate information, we cannot be held responsible for any damages or
problems arising from the use of the information that we have supplied.
Elm Tree Diseases
Elm Tree Links
CONTACT
Quick Elm Facts
ArborScience Inc.
270 Yorkland Blvd.
Suite 160
Toronto, ON
M2J 5C9
Copyright
http://www.elmcare.com/copyright.htm [2/27/02 10:31:18 PM]
Why Prune?
Home > Caring for your Elm > Pruning > Why Prune?
How Trees Work
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Safety First
Dead or dying branches can fall causing injury or property damage. Overgrown
branches can obstruct lines of sight in vital areas such as intersections or
driveways. Trees can come into contact with overhead power lines. Pruning
removes safety hazards.
Better yet, by careful planting, you can avoid many of the potential hazards in the
first place.
Maintenance Pruning
Trees shed weak branches to promote growth in healthier areas. You can help this
process. Remove branches that are in competition for sunlight or that are rubbing
against other.
DED Preventative Pruning
When an elm is under attack from the Dutch elm disease fungus, timely pruning of
infected branches can check the spread of the disease.
Pruning should not take place from early April to late July when the beetle is
active. After the limbs are removed they should be burned or buried.
For more information on DED preventative pruning, click here.
Types of Pruning
http://www.elmcare.com/caring/pruning/why.htm (1 of 2) [2/27/02 10:31:19 PM]
Why Prune?
Copyright
http://www.elmcare.com/caring/pruning/why.htm (2 of 2) [2/27/02 10:31:19 PM]
Types of Pruning
Home > Caring for your Elm > Pruning > Types of Pruning
How Trees Work
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Crown-thinning
With this type of pruning, dead or dying branches are removed from the crown in
order to allow better air movement and light penetration to the tree.
Crown-raising
This type of pruning is performed to provide clearance. Most municipalities have
bylaws specifying minimum branch height beside roads and sidewalks. The lower
branches are removed effectively raising the crown of the tree.
Crown-reduction
When a tree has outgrown the available space, crown-reduction pruning is often
necessary. Upper limbs are pruned to either reduce the height or width of the
crown.
Elm Tree Links
Quick Elm Facts
Proper Pruning Techniques
Copyright
http://www.elmcare.com/caring/pruning/types.htm [2/27/02 10:31:21 PM]
Pruning Technique
Home > Caring for your Elm > Pruning > Technique
How Trees Work
About Elm Trees
Adopting proper pruning techniques is vital for the health of the tree. Cuts should
be made at the point where two branches meet (known as a node). Cuts made in
the middle of a branch (internodal cuts) can result in unhealthy regrowth and slow
wound closure.
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Where To Make Your Cut
The area where the branch meets a major limb is characterized by two features –
the branch collar and the branch bark ridge. The branch collar is underneath the
branch, while the branch bark ridge is above it. This is the point where branches
would naturally be lost. When pruning a branch, it is important to make a cut as
close as possible to these features without actually cutting them. Cutting into the
branch collar will promote decay in the main stem as it takes longer for the tree to
close such a wound.
Elm Tree Links
Quick Elm Facts
Larger Limbs
For larger limbs, special care is required to prevent damage to the tree. If a cut is
made from the branch ridge directly through to the branch collar, often the limbs
weight will cause it to rip away from the stem leading to a large slow-closing
wound. Therefore, first a small undercut should be performed a small distance
(maybe 5cm) away from the collar. Then, a clean topcut can be made on the
outside of the undercut (away from the stem). Finally, a clean cut can be made
just outside the branch collar.
Timing
Copyright
http://www.elmcare.com/caring/pruning/technique.htm [2/27/02 10:31:23 PM]
Timing of Pruning
Home > Caring for your Elm > Pruning > Timing
How Trees Work
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
When
Unlike many other tree species, pruning must be done at a very specific time of
year. Because open wounds attract the elm bark beetle (the major vector for Dutch
elm disease), pruning should never be performed from about mid-April to lateJuly. In fact, some communities have bylaws to this effect. Also, due to presence
of a variety of fungal spores in the fall, if possible, pruning should be avoided. This
leaves early spring as an ideal pruning season. With the growing season to follow,
the tree has ample time to close the wound and regain its vitality.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
How Often
Mature deciduous ornamental trees such as elms should be thoroughly pruned
once every three years with annual minor pruning. In areas where Dutch elm
disease is present, more vigilance is required to allow timely removal of dead or
dying branches. If a tree is noticeably slow to bounce back from a pruning
session, less frequent pruning may be in order.
Pruning Pitfalls
Copyright
http://www.elmcare.com/caring/pruning/timing.htm [2/27/02 10:31:24 PM]
Pruning Pitfalls
Home > Caring for your Elm > Pruning > Pruning Pitfalls
How Trees Work
About Elm Trees
Caring for Your
Elm Tree
Fertilizing
Pruning
Lawn Care
Watering
Obstacles
Disposal
Elm Tree Diseases
Elm Tree Links
Topping
This practice is extremely harmful to trees. Firstly, it involves the sudden removal
of a large proportion of the tree’s foliage which temporarily starves the tree of
needed energy. To compensate for the loss, the tree will promote the growth of
new buds, usually from just below the stub. Homeowners may feel that this new
growth represents healthy regrowth, but this is not the case. The new buds are
structurally weak and superficially anchored to the larger branch. Although very
quick to grow, they can easily break in windy conditions. Thus, the original
purpose of topping (pruning potentially hazardous limbs or controlling upward
growth) is defeated.
Secondly, bark that is suddenly exposed to large amounts of sunlight and heat can
become scalded. This can lead to damage and often death of the limb. This again
creates a potential hazard.
Quick Elm Facts
Thirdly, topping wounds close slowly and sometimes not at all. Insects and
pathogens can therefore gain access to the tree for extended periods of time. This
is a major concern if Dutch elm disease has been spotted in the region.
Finally, topped trees are unattractive and can often contribute to a lowering of
property values.
Copyright
http://www.elmcare.com/caring/pruning/pitfalls.htm [2/27/02 10:31:26 PM]
Leaves
Home > How Trees Work > Structure of a Tree > Leaves
Leaves perform two vital functions for trees. They produce sugars by
photosynthesis and they allow for the distribution of water through transpiration.
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
About Elm Trees
Photosynthesis is a process by which CO2 and water are combined with sunlight
and a pigment called chlorophyll. The chemical reactions result in the production
of sugars which provide energy to the tree. The leaves use some of this energy,
but the majority is transported, in the form of sugar solutions, to other parts of the
tree that require it.
Transpiration, or water loss, also takes place in the leaves. As this occurs, water
is drawn up from the roots through the vascular system to replace lost moisture.
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Roots
Bark
Copyright
http://www.elmcare.com/trees/structures/leaves.htm [2/27/02 10:31:28 PM]
Roots
Home > How Trees Work > Structure of a Tree > Roots
Jump ahead to: Root Structure
Root Growth
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Roots are organs that provide structural stability for trees. Roots also absorb
water and minerals.
Root Structure
Roots are made up of a number of specialized components. The root hairs, tiny
structures extending from the main root stems, have very thin walls which absorb
water and minerals. This mineral solution is passed into the vascular core of the
root from where it is transported throughout the tree. At the tip of the root, there
exists a protective structure called the root cap. These loose cells are shed as the
root grows into the soil.
Different trees have slightly different root systems. Some trees, such as the pine,
have a strong central root called the taproot. This is usually larger than any other
roots and often extends deep into the ground. Because substantial damage to this
root can be fatal to the tree, trees with taproots are generally difficult to transplant.
Other trees, such as the elm or maple, do not have a dominant taproot. Their root
systems are characterized by a large number of roots often closer to the surface.
Top
Root Growth
Generally, root growth is influenced by moisture and gravity. In other words,
unless there are substantial amounts of moisture near the surface, roots tend to
grow downwards through the soil.
Roots are always growing and, like a tree's trunk, they grow both longer and
wider. At the tip of the roots, the growing region is called the meristem. This is
where most of the lengthwise growth takes place. In addition to this, wood is
added to the inside of the root and phloem is added towards the outside.
Top
http://www.elmcare.com/trees/structures/roots.htm (1 of 2) [2/27/02 10:31:29 PM]
Roots
Source: MS Encarta online encyclopedia
Leaves
Bark
Copyright
http://www.elmcare.com/trees/structures/roots.htm (2 of 2) [2/27/02 10:31:29 PM]
Bark
Home > How Trees Work > Structure of a Tree > Bark
Bark is the outer protective covering of tree trunks. The form and structure of bark
can differ greatly from tree to tree. As a result, it is a useful characteristic for tree
identification.
About Elmcare.com
Bark is made up of two layers - outer bark and inner bark.
How Trees Work
Types of Trees
Important Facts
Structure of a Tree
How Trees Breathe
How Trees Drink
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
The outer bark is made up of dead cells. This layer is usually quite thick, but in
certain trees (young birch, for example) it is very thin.
The inner bark, known as the phloem is made up of a thin layer of living
cells. These cells have extremely thin walls allowing water and nutrients (in the
form of sugar solutions) to pass easily throughout the tree. Somewhat akin to
human skin, old bark is shed, and new bark is formed from the inside.
Leaves
Roots
Ask the Experts
Quick Elm Facts
Copyright
http://www.elmcare.com/trees/structures/bark.htm [2/27/02 10:31:31 PM]
Ask the Experts
Home > Ask the Experts
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Due to the overwhelming response we have been
receiving, we are temporarily suspending the Ask the
Experts section of elmcare.com. Our experts are currently
in the field conducting trials for ELMguard and are unable
to keep up with the number of questions we are receiving.
Please check back frequently or enter your e-mail address below to be
informed when the Ask the Experts section is reopened.
Elm Tree Links
Quick Elm Facts
Submit
Perhaps your question has already been answered. Check the categories below
for past questions and answers.
Fertilizing (4)
Watering
Insects (1)
Elms in general (5)
Dutch elm disease (5)
Pruning (2)
Other diseases (2)
Elm Wood (2)
Copyright
http://www.elmcare.com/experts/experts.htm [2/27/02 10:31:33 PM]
new!
Ask the Experts - Fertilizing
Home > Ask the Experts >
Fertilizing
Should I be using fertilizer for my tree?
Will my lawn fertilizer help my elm tree?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
When should I fertilize my elm?
What formulation would you recommend for an elm tree?
Question Should I be using fertilizing for my tree?
Answer
Ask the Experts!
Quick Elm Facts
ELMguard Trials
Fertilizing is an integral part of a comprehensive elm care program.
Elms trees that live in a city lack some of the nutrients it needs to
truly do well.
Question Will my lawn fertilizer help my elm tree?
Answer Probably not. Lawn fertilizer has several characteristics which make
it undesirable for elms. First, it's generally in a granular formulation.
For trees, you want a fertilizer you can put into the ground. Secondly,
the formulations often include chemicals to kill weeds. This can be
harmful for the tree. Thirdly, grass competes with a tree for available
nutrients. Because of this, nutrients will be absorbed by the grass
before they can penetrate the soil to the tree's roots. You should use
a fertilizer specially formulated for trees.
Question
Answer
When should I fertilize my elm?
Fertilization should be done in the spring or the fall. Fall is very good
because there is a lot of moisture in the ground and the roots are
very active.
Question What formulation would you recommend for an elm tree?
http://www.elmcare.com/experts/fert.htm (1 of 2) [2/27/02 10:31:35 PM]
Ask the Experts - Fertilizing
Answer A 5-10-10 or 6-12-12 fertilizer would be ideal for an elm. The first
number is the proportion of Nitrogen. You don't want as much
Nitrogen because that is the mineral that promotes new growth. If
you have too much new growth, the tree can't focus as much on other
important tasks such as building up its defense mechanism.
If your question isn't answered here, send it to us!
Or visit the fertilizing section of elmcare.com.
Copyright
http://www.elmcare.com/experts/fert.htm (2 of 2) [2/27/02 10:31:35 PM]
Ask the Experts - Watering
Home > Ask the Experts > Watering
How should I water my elm tree?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
Question How should I water my elm tree?
Answer When you are watering your tree, you want to get the moisture below
the turf line (below the grass roots). Because of this, a sprinkler is
not very effective. One method is to simply soak the ground with a
hose. This allows the water to penetrate to the tree roots.
Ask the Experts!
Quick Elm Facts
ELMguard Trials
Or visit the watering section of elmcare.com.
Copyright
http://www.elmcare.com/experts/water.htm [2/27/02 10:31:37 PM]
Ask the Experts - Insects
Home > Ask the Experts > Insects
What should I do to control the elm bark beetle population?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
Ask the Experts!
Question What should I do to control the elm bark beetle population?
Answer Elm bark beetles are the major vector of Dutch elm disease. They
carry the fungus on their backs and burrow into elm trees. There are
a number of insecticides that are registered for use in controlling the
elm bark beetle population.
It is estimated, however, that less than 5% of elm bark beetles
actually carry the fungus. The presence of the beetles does not
necessarily indicate the presence of Dutch elm disease. Also, it is
important to consult a professional applicator before using
insecticides.
Quick Elm Facts
ELMguard Trials
If your question is not answered here, send it to us!
Or visit the Elm Tree Diseases section of elmcare.com.
Copyright
http://www.elmcare.com/experts/insects.htm [2/27/02 10:31:38 PM]
Ask the Experts - Elms in General
Home > Ask the Experts > Elms
in General
Can I separate two elms that have grown together?
How suitable is the Siberian elm as a windbreak?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
How do I remove stumps?
What causes the bark to peel away?
Do elm trees lose their leaves in Florida?
Question Can I separate two elms that have grown together?
Ask the Experts!
Quick Elm Facts
ELMguard Trials
Answer Probably the best solution would be to pick the best one, keep it and
remove the other. I hate to suggest that you cut one seedling, but
you will only have problems if you leave them together. I fear that if
you try to separate them you may lose both.
Question How suitable is the Siberian elm for use as a windbreak?
Answer I would have to say the Siberian elm is considered a weed species in
many cities. It is extremely hardy and will grow out of a crack in the
pavement with very little soil available. It is a 'dirty' tree that sheds
branches, leaves, seeds etc. , almost continually. If you are
committed to maintenance then it can be used as a windbreak, but if
the tree is left to grow without pruning it will soon become
unmanageable and unsightly. The species is best used as a hedge
species.
Question How do I remove stumps?
Answer Have someone come with a stump grinder and grind it down al least
6 inches below the grade. If that doesn't work, there are over-thecounter products available at most garden centers that inhibit any
new sprouting.
http://www.elmcare.com/experts/elms.htm (1 of 2) [2/27/02 10:31:40 PM]
Ask the Experts - Elms in General
Question My elm tree seems healthy, but I've noticed that there are large tracts
of bark running vertically from the base up to 3-4 feet that can be
easily peeled away. What may have caused this and what should I
do?
Answer When elms get to be larger in diameter, there is a tendency for outer
bark to loosen to allow for the expansion of the tree. This is also why
bark tends to be furrowed in appearance. Generally, as this is a
natural occurrence, you need not take any special action. To be
sure, however, it is always a good idea to consult a qualified arborist.
Question I live in Florida and I recently bought two elm trees. They both lost
the majority of their leaves. Do elm trees usually lose their leaves
this far south?
Answer American elms are deciduous broadleaf trees and as such, they lose
their leaves in the fall. In the natural habitat, I haven't heard of any
instance where they kept their leaves for the winter. When they are
transplanted into an area with a warmer climate such as Florida,
however, they could potentially act quite differently.
Or visit the About Elms section of elmcare.com.
Copyright
http://www.elmcare.com/experts/elms.htm (2 of 2) [2/27/02 10:31:40 PM]
Ask the Experts - Dutch Elm Disease
Home > Ask the Experts > Dutch
Elm Disease
Is Dutch elm disease a problem in Texas?
How long can DED remain dormant?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
Can you use dead elms for furniture?
Are some species more resistant to DED?
Can Nystatin be used to treat DED?
Question Is Dutch elm disease a problem in Texas?
Ask the Experts!
Quick Elm Facts
ELMguard Trials
Answer From what I can gather, there is an extremely low incidence of DED
in Texas. I was told that there is usually at least one confirmed case
a year in Texas, but there has been no significant wholesale loss of
elms due to DED. The native Cedar elm seems to display some level
of resistance to DED but I do not believe that this has been
extensively tested. The American elm is not a prevalent species in
the state.
Question How long can Dutch elm disease remain dormant in elm trees?
Answer I found out that in one study, the researchers isolated the fungus in
vessels in the tree that had been effectively sealed off in the tree for
25 years. The fungus that was isolated was still viable. If this occurs
in trees it is generally not a threat to survival if the defense reactions
effectively isolate the disease by the end of the growing season. If,
however, the defense reactions are not complete, the fungus may be
able to reach the newly forming vessels in the next growing season.
When this happens there is a much higher likelihood that the disease
will affect the entire tree and eventually kill it.
I must point out that this is not a common occurrence.
Question My Siberian elms died. I don't think it was Dutch elm disease and I
want to use the wood for furniture. Is it safe?
http://www.elmcare.com/experts/ded.htm (1 of 2) [2/27/02 10:31:42 PM]
Ask the Experts - Dutch Elm Disease
Answer Generally, DED does not kill Siberian elm trees. Usually only one
branch will die as the species can effectively fend off the disease. I
would be fairly certain that your trees are not infected with DED. If
you remove all of the bark there should be no risk of bark beetles
breeding in the wood. You should check with the local authorities,
however, as there may be bylaws restricting the use of elm wood.
Question Are some elm species more resistant to Dutch elm disease than
others?
Answer Yes. Species that have coexisted with the Dutch elm disease fungus
for the longest period tend to have the highest degree of resistance.
These species have evolved to develop better defenses against the
pathogen. Scientists now believe that Dutch elm disease originated
in central Asia. Therefore, we would expect that species originating
from Asia would show an increased resistance to DED and in fact
that is what we do see. The Siberian elm, for example, is largely
resistant. Species such as the American elm, however, have only
recently come into contact with the disease and as such have not had
the time to develop immunity.
Scientists are now working towards developing cultivars which exhibit
greater resistance to Dutch elm disease. The Liberty Elm is one
such cultivar.
Question I have heard of an antifungal called Nystatin. Can it be used to treat
Dutch elm disease?
Answer Because Nystatin is an antifungal, it could conceivably have an effect
on Dutch elm disease. The drug was, however, designed for use on
humans and is relatively expensive to procure. A major concern
about the use of Nystatin arises from the fact that it is an antibiotic.
As a result, overuse can lead to more aggressive strains of the
fungus.
Or visit the Dutch elm disease section of elmcare.com.
Copyright
http://www.elmcare.com/experts/ded.htm (2 of 2) [2/27/02 10:31:42 PM]
Ask the Experts - Pruning
Home > Ask the Experts >
Pruning
Does pruning make a tree grow faster?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
Ask the Experts!
Quick Elm Facts
ELMguard Trials
Why can't I prune in my municipality?
Question Does pruning make a tree grow faster?
Answer I'm not sure that pruning will help the tree to grow faster, but it will
help if you prune out weak, crossing and interfering branches and
direct future growth into the good structure. Ideally you should keep
as much foliage as possible so that the tree can produce and
establish a solid root system - especially when the tree is young. I
would consult a local arborist before you do any pruning.
Question There is a law in my municipality against pruning an elm tree, but
other trees can be pruned. Why is that?
Answer That's a good question. The answer lies with the way that Dutch elm
disease is transmitted. The elm bark beetle, which carries the DED
fungus on its back, is most active from mid-spring until late summer.
These beetles are attracted to the open wounds that are left on a tree
after pruning. Therefore, you should only prune an elm when the
beetles are relatively inactive which is in early spring or fall.
Or visit the pruning section of elmcare.com.
Copyright
http://www.elmcare.com/experts/prun.htm [2/27/02 10:31:44 PM]
Ask the Experts - Other Diseases
Home > Ask the Experts > Other
Diseases
How do I know if my tree has elm yellows?
What can I do if my tree has wetwood?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
Ask the Experts!
Question How do I know if my tree has Elm Yellows?
Answer You can test for elm yellows by cutting a small potentially infected
branch and placing it in a sealed glass jar. After a couple of hours,
open the jar and smell inside to see if you detect a wintergreen
odour. This is a telltale sign.
Or visit the elm yellows section of elmcare.com.
Quick Elm Facts
ELMguard Trials
Question What can I do if my tree has wetwood?
Answer In, general, there is not a lot that you can do about Wetwood.
Wetwood is caused by a bacterial infection and is very common in
elms and many other species. The infection causes moisture to be
retained in the wood and also produces metabolic gases that
increase the internal pressures in the tree. Periodically the liquid will
be forced out of the tree through wound sites. The liquid oozes out
and down the tree, where other organisms colonize it. This liquid is
called slime flux and is known to have a foul odour.
Wetwood becomes a problem only when enough infection sites occur
on the tree to compromise its structural integrity. A professional or
consulting arborist should judge this. Otherwise, wetwood can be
viewed as somewhat beneficial, as the moist environment that it
creates in the tree helps to prevent decay fungi from colonizing the
tree.
Or visit the wetwood section of elmcare.com.
http://www.elmcare.com/experts/other_diseases.htm (1 of 2) [2/27/02 10:31:46 PM]
Ask the Experts - Other Diseases
Copyright
http://www.elmcare.com/experts/other_diseases.htm (2 of 2) [2/27/02 10:31:46 PM]
Ask the Experts - Wood
Home > Ask the Experts > Elm
Wood
Can I use elm firewood given to me by a tree removal company?
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm Community
Ask the Experts!
Quick Elm Facts
ELMguard Trials
Is furniture made of elm wood prone to cracking?
Question Can I use elm firewood given to me by a tree removal company?
Answer I would be very concerned about the wood and the possibility of
disease. Tree companies will often have trouble disposing of wood
and will jump at the opportunity of giving it away rather than hauling it
away. Many of them are rather unscrupulous and will tell you what
you want to hear if it is in their best interest. You could very well
spread the disease in your area by having the wood there. Many
jurisdictions have strict bans on elm firewood with stiff penalties if it is
found on your property. There is a characteristic streaking of the
wood that can be seen in infected branches, but sometimes that is
hard to detect if you are not familiar with the symptom. If the wood is
very dry and the bark is loose or absent then there is little to be
concerned about. If not, then you could have a problem. Elms are
very vigorous trees and don't die very easily, so I wonder why the
tree died if it was not DED. I would suggest contacting a local urban
forester or a consulting arborist ASAP, as the bark beetles that
transfer the disease will fly to healthy trees any time soon. This could
be a serious problem for your neighbourhood.
Question Is furniture made of elm wood prone to cracking in dry areas?
http://www.elmcare.com/experts/wood.htm (1 of 2) [2/27/02 10:31:48 PM]
Ask the Experts - Wood
Answer It seems that if that much time has been taken to dry the wood it
should be fairly dry. The only question remaining is whether it was
dried outside or inside. If outside, it will probably have about 15%
residual moisture and that can drop to 4-5% inside in the driest time
of the year. The other question raised is how was the piece cut? If the
slice was made along the grain of the wood there is a much lower
likelihood that it will split than if the piece was cut on an angle across
the grain. You should also see how the final finish has been applied
and how well all the surfaces have been sealed. The finish should be
highly impermeable to moisture.
Copyright
http://www.elmcare.com/experts/wood.htm (2 of 2) [2/27/02 10:31:48 PM]
Identifying Silhouette
Home > About Elms > Identifying Elms > Silhouette
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
The American elm is one of the
largest trees in eastern North
America and it grows to a height of
35m with a trunk diameter of
175cm. The base of the tree is
reinforced by prominent root flares
and a shallow and wide-spreading
root system. A few large upright
limbs support many outwardly
fanning branches.
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
The tips of these branches often
droop downwards contributing to the
overall graceful umbrella-like
silhouette. Fully mature trees can
live as long as 300 years, although in areas which have experienced Dutch elm
disease, young trees less than 30 years old are the norm.
Leaves
Bark
Copyright
http://www.elmcare.com/about_elms/identifying/identifying_silhouette.htm [2/27/02 10:31:50 PM]
Identifying Leaves
Home > About Elms > Identifying Elms > Leaves
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm leaves are deciduous and
alternate in two rows along the
shoot. The shape is oval and
tapers towards a point. The edge
is ragged and saw-toothed and
veins are prominent. The size is
dependent on the species, but the
leaves of an American elm are
usually between 10 and 15 cm in
length.
Notice the uneven base on each
leaf. This characteristic is
common in elms and is a good
thing to look for.
Elm Tree Links
Quick Elm Facts
Silhouette
Bark
Copyright
http://www.elmcare.com/about_elms/identifying/identifying_leaves.htm [2/27/02 10:31:52 PM]
Identifying Bark
Home > About Elms > Identifying Elms > Bark
How Trees Work
The bark of an American elm is dark grayishbrown becoming mottled ash-gray as the tree
ages. The surface is deeply furrowed with broad
obliquely intersecting ridges.
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Silhouette
Leaves
Copyright
http://www.elmcare.com/about_elms/identifying/identifying_bark.htm [2/27/02 10:31:54 PM]
The Cultivated Elm
Home > About Elms > The Elm Story > The Cultivated Elm
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Long Ago
We have been using the elm tree for thousands
of years since the first farmers found them in
ancient forests.
In western Europe, farmers used elm leaves
and branches as cattle feed. Fisherman traded
for elm leaves to boil and eat in times of
scarcity.
Romans used living elms to support their
grapevines - a practice called "marrying the
vine to the elm." They also selectively bred elms producing many of the species
we see today throughout their former Empire.
In North America, the Iroquois used the bark of elms to make canoes, rope,
utensils, and roofing for their homes. The Ainu, native people of Japan, used elm
bark for clothing.
Luxurious Shade
Until recently, elms were the predominant shade tree in North America.
Elms, like other shade trees, are nature’s air conditioners. They help to cool not
just by providing shade but by the transpiration of water from their leaves. In fact,
the cooling effect of one urban elm tree is equivalent to five air conditioning units.
And like all trees, elms are a natural air purifier converting carbon dioxide into
oxygen.
Rural Roots
http://www.elmcare.com/about_elms/elms_and_humans.htm (1 of 2) [2/27/02 10:31:57 PM]
The Cultivated Elm
The hardy elm trees readily
endures the severe winters of the
US Midwest and the Canadian
Prairies.
Shelterbelts of elm trees provide
shade for livestock and protect
farms from biting winds and storms.
Because their wood is particularly
tough, farmers often left elms
standing when clearing fields. To this day, you can see solitary elms in the middle
of large open fields.
Industrial Benefits
The tough cross-grained wood of the elm tree is highly resistant to splitting. It is
used to make baskets, furniture, and flooring. Hockey sticks, wheel hubs and boat
frames have all taken advantage of the special properties of elm wood.
A Special Affection
Appreciation of the elm tree is evidenced by North American settlers, who named
the elm “the lady of the forest”. Countless poems have been penned about the
stately giant.
It also figures in many historical events. For example, George Washington first
drew his sword underneath the Washington Elm in 1775. Poet James Russell
Lowell wrote of Washington:
“What figure more immovably august,
Than that grave strength so patient and so pure.”
(Atlantic Monthly: 1875 36)
What better words to describe the elm itself?
Copyright
http://www.elmcare.com/about_elms/elms_and_humans.htm (2 of 2) [2/27/02 10:31:57 PM]
Living History
Home > About Elms > The Elm Story > Living History
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
From the Liberty Elm in Boston to the Wolseley Elm
in Winnipeg, elms have been focal points of
community and political action.
Click on one of the following to learn more:
The Liberty Elm
The Wolseley Elm
The Washington Elm
William Penn's Elm
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Courtesy APS (www.scisoc.org)
Do you know of any historically significant elms not listed above?
If so, e-mail us at [email protected]
Copyright
http://www.elmcare.com/about_elms/history/elms_living_history.htm [2/27/02 10:31:59 PM]
Liberty Elm
Home > About Elms > The Elm Story > Living History > The Liberty Elm
Boston's Liberty Elm is arguably the first symbol of freedom for the United States.
It was a backdrop to oration, celebration, and revolution.
How Trees Work
About Elm Trees
On August 14, 1765, colonists hung effigies of Lord Butte and Andrew Oliver in
protest against the despised Stamp Act. Revolutionaries held rallies and speeches
around the tree.
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
It was cut down by departing British soldiers in 1775.
Back to "Living History"
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Do you know of any historically significant elms?
Copyright
http://www.elmcare.com/about_elms/history/liberty_elm_boston.htm [2/27/02 10:32:00 PM]
Wolseley Elm
Home > About Elms > The Elm Story > Living History > The Wolseley Elm
How Trees Work
In Winnipeg, Manitoba, in the late 1950's, city officials wanted to remove a
majestic elm to make way for a new street. Outraged, a group of women locked
arms around the tree in protest. The city backed down and the tree was saved.
About Elm Trees
Years later, the tree was lost to vandalism. But after it was taken down, a new elm
was planted to take its place.
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
The Wolseley Elm is now part of Winnipeg's folklore.
Source: Manitoba's "Coalition to Save the Elms." (www.savetheelms.mb.ca)
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Do you know of any historically significant elms not listed above?
Copyright
http://www.elmcare.com/about_elms/history/wolseley_elm.htm [2/27/02 10:32:02 PM]
Washington Elm
Home > About Elms > The Elm Story > Living History > The Washington Elm
How Trees Work
George Washington took control of the
revolutionary army and first drew his sword
underneath this tree in 1775.
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
The tree died in 1923.
Library of Congress, Prints and Photographs
Division, Detroit Publishing Company Collection
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/history/washington_elm.htm [2/27/02 10:32:04 PM]
William Penn's Elm
Home > About Elms > The Elm Story > Living History > William Penn's Elm
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
William Penn signed the Treaty of Shackamaxon with
the Delaware Indians underneath a huge elm.
This treaty formalized the purchase of land in
Pennsylvania. It also marked the beginning of an
amicable relationship between the Quakers and the
Indians that lasted for almost a hundred years.
In 1810, a storm blew the tree down. It was a grand 280 years old. Today, items
made from the wood of that elm are considered valuable antiques.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/history/william_penn_elm.htm [2/27/02 10:32:05 PM]
Elms in Literature
Home > About Elms > The Elm Story > Elms In Literature
How Trees Work
The elm has enchanted and inspired poets for countless
generations.
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Click on a name to read more:
Robert Frost
John Milton
Ralph Waldo Emerson
Robert Browning
Herman Melville
Erasmus Darwin
Denise Levertov
William Butler Yeats
Phillip Freneau
Alfred Tennyson
William Wordsworth
Sylvia Plath
John Clare
Oliver Wendell Holmes
Ovid
Virgil
Theocritus
Copyright
http://www.elmcare.com/about_elms/literature/elms_in_literature.htm [2/27/02 10:32:07 PM]
Robert Frost
Home > About Elms > The Elm Story > Elms in Literature > Robert Frost
Robert Frost (1874-1963)
From "The Cocoon"
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
As far as I can see, this autumn
haze
That spreading in the evening air
both ways
Makes the new moon look
anything but new
And pours the elm-tree meadow
full of blue,
Is all the smoke from one poor
house alone.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Back
Copyright
http://www.elmcare.com/about_elms/literature/robert_frost.htm [2/27/02 10:32:09 PM]
John Milton
Home > About Elms > The Elm Story > Elms in Literature > John Milton
John Milton (1608-1674)
How Trees Work
From "Comus"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Perhaps some cold bank is her bolster
now,
Or 'gainst the rugged bark of some broad
elm
Leans her unpillowed head fraught with
sad fears
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Back
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/john_milton.htm [2/27/02 10:32:11 PM]
Ralph Waldo Emerson
Home > About Elms > The Elm Story > Elms in Literature > Ralph Waldo Emerson
How Trees Work
Ralph Waldo Emerson (1803-1882)
From "Compensation"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Man's the elm, and Wealth the vine,
Stanch and strong the tendrils twine
Biology of Elms
Caring for Your Elm
Back
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/ralph_waldo_emerson.htm [2/27/02 10:32:14 PM]
Robert Browning
Home > About Elms > The Elm Story > Elms in Literature > Robert Browning
Robert Browning (1812~1889)
How Trees Work
"Oh, to be in England"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Oh, to be in England
Now that April's there,
And whoever wakes in England
Sees, some morning, unaware,
That the lowest boughs and the brushwood sheaf
Round the elm-tree bole are in tiny leaf
Round the chaffinch sings on the orchard bough
In England - now!
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Back
Copyright
http://www.elmcare.com/about_elms/literature/robert_browning.htm [2/27/02 10:32:15 PM]
Herman Melville
Home > About Elms > The Elm Story > Elms in Literature > Herman Melville
How Trees Work
Herman Melville (1819-1891)
From "Malvern Hill"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
We elms of Malvern Hill
Remember everything;
But sap the twig will fill:
Wag the world how it will,
Leaves must be green in Spring
Caring for Your Elm
Elm Tree Diseases
Back
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/herman_melville.htm [2/27/02 10:32:17 PM]
Erasmus Darwin
Home > About Elms > The Elm Story > Elms in Literature > Erasmus
Erasmus Darwin (1731~1802)
About Elmcare.com
How Trees Work
From "Untitled"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
The Elm Community
Herb, shrub, and tree, with strong emotions
rise
For light and air, and battle in the skies;
Whose roots diverging with opposing toil
Contend below for moisture and soil;
Round the tall Elm the flattering Ivies bend,
And strangle, as they clasp, their struggling
friend.
Back
Ask the Experts!
Quick Elm Facts
ELMguard Trials
Copyright
http://www.elmcare.com/about_elms/literature/erasmus_darwin.htm [2/27/02 10:32:20 PM]
Darwin
Denise Levertov
Home > About Elms > The Elm Story > Elms in Literature > Denise Levertov
Denise Levertov (1923-1997)
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
"Living While it May"
The young elm that must be cut
because its roots push at the house wall
taps and scrapes my window
urgently - but when I look round at it
remains still
Denise Levertov by David Geier
Caring for Your Elm
Photography
Elm Tree Diseases
Elm Tree Links
Back
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/denise_levertov.htm [2/27/02 10:32:22 PM]
William Butler Yeats
Home > About Elms > The Elm Story > Elms in Literature > William Butler Yeats
William Butler Yeats (1865~1939)
How Trees Work
From "My House"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
An ancient bridge, and a more ancient
tower,
A farmhouse that is sheltered by its wall,
An acre of stony ground,
Where the symbolic rose can break in
flower,
Old ragged elms, old thorns innumerable.
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/william_butler_yeats.htm [2/27/02 10:32:24 PM]
Phillip Freneau
Home > About Elms > The Elm Story > Elms in Literature > Phillip Freneau
Phillip Freneau (1752~1832)
How Trees Work
From "The Indian Burying Ground"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Here still an aged elm aspires,
Beneath whose far-projecting shade
(And which the shepherd still admires)
The children of the forest played.
Biology of Elms
Caring for Your Elm
Back
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/phillip_freneau.htm [2/27/02 10:32:26 PM]
Alfred Tennyson
Home > About Elms > The Elm Story > Elms in Literature > Alfred Tennyson
Alfred Tennyson (1809~1892)
How Trees Work
From "Untitled"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
And gathering freshlier overhead
Rocked the full-foliaged elms, and swung
The heavy-folded rose, and flung
The lilies to and fro, and said,
"The dawn, the dawn," and died away;
And East and West, without a breath,
Mixt their dim lights, like life and death,
To broaden into boundless day.
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
From "Come Down, O Maid"
Sweeter thy voice, but every sound is sweet
Myriads of rivulets, hurrying through the lawn,
The moan of doves in immemorial elms,
And murmuring of innumerable bees.
Back
Copyright
http://www.elmcare.com/about_elms/literature/alfred_tennyson.htm [2/27/02 10:32:28 PM]
William Wordsworth
Home > About Elms > The Elm Story > Elms in Literature > William Wordsworth
William Wordsworth (1770~1850)
How Trees Work
From "Untitled"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Thither I came, and there, amid the gloom
Spread by a brotherhood of lofty elms
Appeared a roofless hut, four naked walls
That stared upon each other...
Biology of Elms
Caring for Your Elm
Back
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/william_wordsworth.htm [2/27/02 10:32:30 PM]
Sylvia Plath
Home > About Elms > The Elm Story > Elms in Literature > Sylvia Plath
Sylvia Plath (1932~1963)
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
"Elm"
I know the bottom, she says. I know it with my
great tap root;
It is what you fear.
I do not fear it: I have been there.
Is it the sea you hear in me,
Its dissatisfactions?
Or the voice of nothing, that was you madness?
Love is a shadow.
How you lie and cry after it.
Listen: these are its hooves: it has gone off, like a
horse.
All night I shall gallup thus, impetuously,
Till your head is a stone, your pillow a little turf,
Echoing, echoing.
Or shall I bring you the sound of poisons?
This is rain now, the big hush.
And this is the fruit of it: tin white, like arsenic.
I have suffered the atrocity of sunsets.
Scorched to the root
My red filaments burn and stand,a hand of wires.
Now I break up in pieces that fly about like clubs.
A wind of such violence
Will tolerate no bystanding: I must shriek.
The moon, also, is merciless: she would drag me
Cruelly, being barren.
Her radience scathes me. Or perhaps I have caught her.
I let her go. I let her go
Diminished and flat, as after radical surgery.
How your bad dreams possess and endow me.
I am inhabited by a cry.
http://www.elmcare.com/about_elms/literature/sylvia_plath.htm (1 of 2) [2/27/02 10:32:31 PM]
Sylvia Plath
Nightly it flaps out
Looking, with its hooks, for something to love.
I am terrified by this dark thing
That sleeps in me;
All day I feel its soft, feathery turnings, its malignity.
Clouds pass and disperse.
Are those the faces of love, those pale irretrievables?
Is it for such I agitate my heart?
I am incapable of more knowledge.
What is this, this face
So murderous in its strangle of branches?-Its snaky acids kiss.
It petrifies the will. These are the isolate, slow faults
That kill, that kill, that kill.
Back
Copyright
http://www.elmcare.com/about_elms/literature/sylvia_plath.htm (2 of 2) [2/27/02 10:32:31 PM]
John Clare
Home > About Elms > The Elm Story > Elms in Literature > John Clare
John Clare (1793-1864)
How Trees Work
From "The Elm Tree"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Old favourite tree thoust seen times change
But change till now did never come to thee
For time beheld thee as his sacred dower
And nature claimed thee her domestic tree.
Biology of Elms
Caring for Your Elm
Back
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/john_clare.htm [2/27/02 10:32:34 PM]
Oliver Wendell Holmes
Home > About Elms > The Elm Story > Elms in Literature > Oliver Wendell Holmes
Oliver Wendell Holmes (1809-1894)
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
The hubs of logs from the Settler's ellum,
Last of its timber, they couldn't sell'em,
Never an axe had seen their chips,
And the wedges flow from between their lips,
Their blunt ends frizzled like celery tips.
Biology of Elms
Back
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/oliver_wendell_holmes.htm [2/27/02 10:32:36 PM]
Ovid
Home > About Elms > The Elm Story > Elms in Literature > Ovid
Ovid (43 B.C.~A.D. 17)
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
If that fair elm alone should stand,
No grapes would glow with gold and tempt the hand,
Or if that vine without her elm should grow,
T'would creep, a poor neglected shrub below.
From "Untitled"
Help bucksome God then! so may the lov'd Vine
Swarm with num'rous grapes, and big with Wine
Load the kind Elm, and so thy Orgyes be
With priests lowd showtes, and Satyrs kept to thee!
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Back
Copyright
http://www.elmcare.com/about_elms/literature/ovid.htm [2/27/02 10:32:38 PM]
Virgil
Home > About Elms > The Elm Story > Elms in Literature > Virgil
How Trees Work
Virgil (70~19 B.C.)
From "Untitled"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
And great gods eke aggrievèd with our town.
I saw Troye fall down in burning gledes,
Neptunus' town clean razèd from the soil,
Like as the elm forgrown in mountains high,
Round hewen with axe, that husbandmen
With thick assaults strive to tear up, doth threat,
And hackt beneath trembling doth bend his top,
Till gold with strokes, giving the latter crack,
Rent from height, with ruin it doth fall.
Elm Tree Links
Quick Elm Facts
Back
Copyright
http://www.elmcare.com/about_elms/literature/virgil.htm [2/27/02 10:32:39 PM]
Theocritus
Home > About Elms > The Elm Story > Elms in Literature > Theocritus
Theocritus
How Trees Work
From "The Death of Daphnis"
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Then rest we in the shadow of the elm
Fronting Priapus and the Fountain-nymphs.
Biology of Elms
Back
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/literature/theocritus.htm [2/27/02 10:32:41 PM]
Elms in Mythology
Home > About Elms > The Elm Story > Elms in Mythology
Elm trees have entered our mythology - a mark of their prominence in the lives of
early civilizations.
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Germanic tribes included the elm in their creation myth, and Mongols incorporated
it in a wedding prayer.
Germanic Creation Myth
The ancient Germanic peoples who came to inhabit much of Europe, believed that
three gods, Odin, Vili and Ve, created the world.
According to the myth, these three gods were walking by the sea examining their
handiwork when they came upon two fallen trees. One was an ash, the other an
elm. Odin imbued them with the spark of life. Vili endowed them with spirit and a
thirst for knowledge. Ve gave them the gift of five senses.
When they had finished, the fallen trees resembled the gods themselves. Out of
the ash came man. Woman was created from the elm and her name was Embla.
(Source: "Mythologies" compiled by Yves Bonnefoy v. 1, p.281)
Mongol Wedding Prayer
"Mother Ut (Fire), Mistress of Fire, descended from the elms on the tops of the
Khangai-Khan and the Burkhatu-Khan mountains. Thou, who wast born when
Heaven and Earth parted, who camest forth from the footprints of Mother Ötygen
(Earth), thou creation of Tengeri-Khan. Mother Ut, thy father is the hard steel, thy
mother the flint, thy ancestors, the elm trees. Thy brightness reaches the heavens
and spreads over the earth. Thy brightness reaches the Heaven-dweller, nursed
by the Mistress Uluken.
Goddess Ut, we offer thee yellow butter and a yellow-headed white sheep. Thine
are this brave boy and the beautiful bride, the slender daughter."
(Source: "Mythology of All Races" vol. iv, Uno Holmberg, p.453)
http://www.elmcare.com/about_elms/mythology/elm_in_mythology.htm (1 of 2) [2/27/02 10:32:42 PM]
Elms in Mythology
Copyright
http://www.elmcare.com/about_elms/mythology/elm_in_mythology.htm (2 of 2) [2/27/02 10:32:42 PM]
Elmcare.com - The page you are looking for has not been found.
Home > Page Not Found
Sorry
How Trees Work
About Elm Trees
Unfortunately, the page you are looking for could not be found. It may have been
moved to another location, or it no longer exists.
Caring for Your Elm
Elm Tree Diseases
Click on a menu item to explore, or click here to go back to the home page.
Elm Tree Links
Quick Elm Facts
Copyright
http://www.elmcare.com/community/research/research.htm [2/27/02 10:32:44 PM]
Contact Us
Home > Contact Us
Although we cannot answer every e-mail we receive, we will
read every one and do our best to reply.
How Trees Work
E-mail Address
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Comment
Elm Tree Links
Quick Elm Facts
Submit
Reset
Or, contact us at:
ArborScience Inc.
270 Yorkland Blvd., Suite 160
Toronto, ON
Canada
M2J 5C9
Ph: 416-491-1436
Fax: 416-491-5343
Copyright
http://www.elmcare.com/contactus.htm [2/27/02 10:32:47 PM]
http://www.elmcare.com/images/hubbes_lab.jpg
http://www.elmcare.com/images/hubbes_lab.jpg [2/27/02 10:32:50 PM]
Hubbes1 Abstract
Home > Elm Community > Research > Abstract
About This Site
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm
Community
Research
Community
Ask the Experts!
Quick Elm Facts
ELMguard Trials
The American Elm and Dutch Elm Disease
M. Hubbes
Faculty of Forestry, University of Toronto
Abstract
Shortly after World War I, a new disease previously unknown among elms,
emerged in Holland. It spread rapidly from Europe to Great Britain (1927), United
States (1930), and Canada (1945), killing millions of elms. The disease known, as
Dutch elm disease (DED) is a wilt disease, caused by the fungus Ophiostoma
ulmi. It is transmitted from tree to tree by elm bark beetles (scolytid) vectors.
Numerous attempts to control the disease have concentrated on the reduction of
insect vector populations, exploitation of natural host resistance, extensive
application of fungicides and integrated pest management. In spite of these efforts
in Canada, the disease continues to migrate westwards threatening the elm
populations in Saskatchewan and Alberta. Today there are approximately 700,000
elm shade trees in cities and towns across Canada and their value exceeds $2.5
billion dollars.
With the advance of molecular biology new, powerful tools are now available to
study, in greater detail, the molecular and biochemical mechanisms of the DED
pathogen, with particular reference to the mechanisms that induce host defenses.
A glycoprotein, has been isolated and identified such that when injected either in
liquid or pellet form into the elm tree, significantly reduced the wilting symptoms of
both 5 year old elm seedlings and 10 cam diameter trees. The elicitor induces a
chain of defensive reactions that prevent the rapid spread of the fungus within the
vascular system of the host.
Click here to view the entire article.
http://www.elmcare.com/community/research/hubbes1abstract.htm (1 of 2) [2/27/02 10:32:53 PM]
Hubbes1 Abstract
Copyright
http://www.elmcare.com/community/research/hubbes1abstract.htm (2 of 2) [2/27/02 10:32:53 PM]
Elmcare.com - Hubbes 1
Home > Elm Community > Research > Abstract > Article
About Elmcare.com
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
The Elm
Community
Research
Community
Ask the Experts!
Quick Elm Facts
ELMguard Trials
The American Elm and Dutch Elm Disease
M. Hubbes
Faculty of Forestry, University of Toronto
Abstract
Shortly after World War I, a new disease previously unknown among elms,
emerged in Holland. It spread rapidly from Europe to Great Britain (1927), United
States (1930), and Canada (1945), killing millions of elms. The disease known, as
Dutch elm disease (DED) is a wilt disease, caused by the fungus Ophiostoma
ulmi. It is transmitted from tree to tree by elm bark beetles (scolytid) vectors.
Numerous attempts to control the disease have concentrated on the reduction of
insect vector populations, exploitation of natural host resistance, extensive
application of fungicides and integrated pest management. In spite of these efforts
in Canada, the disease continues to migrate westwards threatening the elm
populations in Saskatchewan and Alberta. Today there are approximately 700,000
elm shade trees in cities and towns across Canada and their value exceeds $2.5
billion dollars.
With the advance of molecular biology new, powerful tools are now available to
study, in greater detail, the molecular and biochemical mechanisms of the DED
pathogen, with particular reference to the mechanisms that induce host defenses.
A glycoprotein, has been isolated and identified such that when injected either in
liquid or pellet form into the elm tree, significantly reduced the wilting symptoms of
both 5 year old elm seedlings and 10 cam diameter trees. The elicitor induces a
chain of defensive reactions that prevent the rapid spread of the fungus within the
vascular system of the host.
Introduction
Almost 80 years ago Dutch scientists reported the dramatic appearance of a new
disease on elms in Holland. The disease quickly became known as Dutch elm
disease (DED). It is caused by the fungus Ophiostoma ulmi (sensus lato), and has
claimed the life of millions of stately elm trees in Europe and North America. Elms,
and in particular the American elm (Ulmus americana), have been an
http://www.elmcare.com/community/research/hubbes1.htm (1 of 22) [2/27/02 10:33:01 PM]
unmistakable cultural and historic landmark of the North American continent. The
tree’s tall and majestic growth combines beauty and grace, placing it among the
most desirable shade tree in our cities and villages. Planted along boulevards and
streets, their crowns span roads and houses providing clean air, coolness during
hot summer days and shelter against UV radiation. The New York Times, in a
February 26, 1989 article, claimed that a large tree is equivalent to five air
conditioning units, playing a very important energy conservation role in our
ecosystem.
Shortly after World War I, in 1918, a new, previously unknown disease of elms
emerged in Holland, which caused yellowing and then wilting of leaves as well as
rapid tree death. The disease spread like a plague and traveled quickly from
Europe to Great Britain (1927) and reached the United States in 1930 (Campana
and Stipes 1981). Although some tree losses occurred in 1927 in England, it was
the appearance of a new strain of the plague in the late 1960s that severely
decimated the elm populations (Gibbs 1981). By 1980, 17 million of the 23 million
previous existing elms had been killed in southern England, causing extensive
economic, esthetic and environmental losses.
Around 1930 there were approximately 77 millions elm trees in cities and towns
across North America. The introduction of the disease had a devastating effect.
For example, by 1976 municipalities in the northeastern United States lost 56% of
their original elm population (Huntley 1982).
Equally significant, a second introduction of the disease to the North American
continent at Sorell, Quebec, Canada in 1945 (Pomerleau 1981) initiated one of the
largest mass destruction of trees ever witnessed, particularly when the disease
fronts from the US and eastern Canada met to migrate westwards. Of the 77
millions elms in the US prior to the disease introduction, only about 34 million
survived by 1976. In Canada the eastern provinces, New Brunswick, Quebec, and
Ontario also suffered major losses. More than 600,000 elms were quickly killed in
Quebec and Toronto’s 35,000 elm tree population was rapidly reduced by 80%
(Huntley 1982). Presently the disease front has reached the elm populations of
Saskatchewan and threatens those of Alberta. This situation causes great concern
to private citizens as well as provincial and municipal authorities. In the prairie
provinces, elms constitute the majority of shade trees in cities and villages. No
other tree is better suited than the elm to withstand the harsh winter climate and
urban environmental stresses in these regions, with its high winds, extreme
temperatures and road salt. Therefore the great efforts of the City of Winnipeg for
example to save their elms through a fully integrated management program, allows
the City to claim itself as the City of elms. However, in spite of this, successful
control programs after 21 years the losses of trees due to DED went from 2.5% to
near 5.0% annually in 1996. Winnipeg’s American elm population still exceeds
200,000 in number. Today there are about 700,000 elms as shade trees in cities
and towns across Canada and their value well exceeds $2.5 billion. The average
elm tree value is based on the data given by Westwood (1991).
Disease control
The DED fungus is mainly transmitted from tree to tree by the European elm bark
beetle Scolytus multistriatus and the native elm bark beetle Hylurgopinus rufipes
(Parker et al. 1947, Jin et al. 1996). Infection, by DED usually occurs from late May
to July while the trees are producing “early wood” in the form of large vessel cells
(Pomerleau 1968, Smalley and Guries 1993). Therefore, the spring-maturating
adults of the European elm bark beetles and the over wintering adults of native
elm bark beetles are the most common vectors of the disease (Pomerleau 1965,
Lanier 1978, Lanier and Peacock 1981, Webber 1990). In addition the fungus may
also move internally from tree to tree through root grafts (Stipes and Campana
1981).
Numerous attempts to control the disease have concentrated on three processes:
reducing the vector populations namely the elm bark beetles (Lanier 1978,
O’Callahan and Fairhurst 1983, Jin et al. 1996), the exploitation of natural host
resistance (Ouellett and Pomerleau 1965, Holmes 1976, Lester 1978, Stipes and
Campana 1981, Heybroek 1983, Smalley and Guries 1993, Ware and Miller 1997),
and extensive application of fungicides (Smalley 1978, Stennes and French 1987).
For the most part, these efforts have not produced the expected results of DED
control (Stipes and Campana 1981, Sticklen et al. 1991).
Reduction of vector populations
Control of elm bark beetles, via chemical insecticides still seems the preferred
choice in areas of high beetle populations to reduce the inoculum potential.
However, in the long run this option is not viable because of the potential negative
impact of the chemical insecticides to the environment and therefore can only be
recommended for very specific situations. Particular attention must also be given
to the selection of correct application equipment otherwise spraying is not very
effective (Roy et al. 1988). The use of biological control agents such as insect
parasitic (entomopathogenic) nematodes against bark beetles has not yet been
exploited and awaits further development (Tomalak et al. 1989). The same is also
true for the Lepidopteran BT toxins (Sticklen et al. 1991). The use of pheromone
traps for vector control has great attraction from an environmental point of view.
However it did not gain the expected momentum because the results were not as
anticipated (Birch et al. 1981, Sticklen et al. 1991). Lanier (1989) reported on the
usefulness of elm bark beetle trap trees for control of DED. This method seems
very appealing, but awaits its wider testing application and has little use in many
towns and cities because trees cannot be spared for traps. Sanitation, though
expensive, is imperative for a successful DED control program, by removing
infected tree parts, or dead trees that harbor beetle populations as well as the
perfect and imperfect stage of the fungus. If not removed and destroyed, these
dead trees are a major source of inoculum. However, sanitation alone is unable to
halt the progress and spread of the disease (Pomerleau 1981).
Chemical control
The introduction of several benzimidazole systemic fungicides has prompted a
number of investigations on the effect of these compounds for DED control. Of
these, benomyl has been tested against O. ulmi (Kondo et al. 1973). Another
chemically related compound known as “Arbotect 20-S” has also been reported as
active against the fungus (Smalley 1978, Prosser 1998). Attempts to overcome
uptake and solubility problems caused by the tree were made by injecting the
chemical into the stem or by uptake experiments through the roots (Kondo 1978,
Roy et al. 1980). Compartmentalization of the tree (Shigo and Campana 1977), in
response to wounding during injection, solubility problems with the chemical, as
well as the ability of the pathogen to develop resistance against the fungicide
(Bernier and Hubbes 1990a, b, Schreiber 1993), and economic reasons did not
lend themselves for very large scale application of these fungicides.
Dutch elm disease is a vascular disease. To effectively colonize its host, the DED
fungus has to invade a large number of vessels and can therefore not rely on its
passive travel in the transpiration stream of a limited number of vessels. It has to
spread from vessel to vessel. Pit membranes are the places where this can occur.
Spores have to germinate and their hyphae penetrate through the membranes.
Scheffer et al. (1988) reported that sterol biosynthesis inhibitors that interfere in
the hyphae formation in O. ulmi suppressed disease development in two Dutch
elm clones. Among a number of chemical derivatives fenpropimorph gave the best
results. The problem is that this chemical renders the tree frost sensitive. Very
recently another compound, a triazole derivative fungicide propiconazole, also
known as “Alamo”, has been introduced for DED control. It is too soon to judge its
effectiveness. Some tests appear encouraging, while others were not as
successful as those were with “Arbotect 20-S” (Prosser 1998). However the
manufacturer has withdrawn this latter product from the Canadian market.
Natural host resistance
The prospects for developing trees with genetic resistance to DED range from
uncertain (Ouellett and Pomerleau 1965, Holmes 1976) to very well (Heybroek
1993, Smalley and Guries 1993, Smalley et al. 1993, Ware and Miller 1997).
Earlier efforts to select and breed American elms (Ulmus americana) for DED
resistance were disappointing. All North American species (U. rubra, U. thomasii,
U. alata, U. serotina, and U. erassifolia) are susceptible to DED. U. americana is
the most susceptible. Therefore efforts were also directed towards the
development of genetic combinations from European and Asian gene pools
(Smalley and Guries 1993, Smalley et al. 1993, Townsend and Santamour 1993,
Sherald 1993, Ware and Miller 1997). A number of selections with superior
resistance to DED were made of which the American “Liberty” elms were the most
promising ones. There is a problem with these selections, as the basis for their
resistance is unknown to scientists and therefore no estimates can be made as to
whether this resistance will last or not. Small changes in the genetic background of
the fungal population or changes in the physiology of the host as it ages may
cause loss of resistance. Indeed, the DED fungus attacks some of the formerly
resistant “Liberty” elms (A.L Shigo, personal communication).
It has been debated how the DED fungus kills its host. I believe that , a final
solution to these problems can only be expected through application of modern
methods of molecular biology by identification, isolation and subsequently directed
rearrangement of genes controlling pathogen (DED) virulence and genes
governing the host’s defense. Once the genetic bases of pathogen virulence and
host resistance have been clarified, trees with long term tolerance towards the
pathogen can be developed (Hubbes 1981, 1993). This for example has been
achieved by the Siberian elm (U. pumila) probably through natural selection.
The fact that the Asian elms show resistance towards DED led to the assumption
that DED originated in Asia. Recent investigations place its origin in the Himalayas
(Brasier and Mehrotra 1995).
Although the development of resistant elms may satisfy the long-term strategy of
DED control, effective protection of the existing elm populations in our cities and
villages still remains a problem. In the past, there has been no lack of efforts to
control the pathogen by biological means with the use of antagonistic
microorganisms such as bacteria (Mazzone et al. 1982, Strobel and Myers 1982,
Holmes and Plourde 1982, White 1982, Shi and Brasier 1986), fungi and virus
particles (Hoch et al. 1985, Rogers et al. 1986, Webber 1987, Bernier et al. 1996).
Some of the organisms showed promise, but their broad application as control
agents has not yet been achieved. It is surprising that most of these treatments
were conducted solely with the view to inhibit the fungal growth by direct
antagonism, while the role of the host’s defense reactions was ignored. Field
observations show that some trees have the means to defend themselves
successfully against the invasion of the DED pathogen by restricting the spread of
the fungus in their vessels. We assume if the mechanisms of this defense reaction
could be clarified and their genetic basis understood they might well form a solid
basis for disease control and resistance breeding.
The pathogen and its strains
In the early 1970’s, the observation that the population of O. ulmi was composed
of two major group of strains, the aggressive and non-aggressive group, gave rise
to numerous assumptions to explain pathogenicity and virulence (Gibbs et al.
1972, Bernier 1983). The non-aggressive isolates induce slower development for
foliar symptoms during the first year of infection, a difference that tends to
disappear during the second year (Schreiber and Townsend 1976). Scala et al.
(1997) reported similar results. Isolates of the aggressive group very quickly
induce severe wilting symptoms leading to the death of the hosts.
Aggressive and non-aggressive group of isolates also differ in a wide range of
morphological and physiological characters. Crossing between the two groups is
believed to be rare under field conditions (Gibbs and Brasier 1973, Brasier 1977,
1979, 1982). The aggressive group has been further subdivided in two races
termed as the European (EAN) and North American (NAN) races (Brasier 1988).
Initial separation of the isolates into the various sub-groups based on
morphological characters was often erratic. Various well known laboratory
techniques to identify isolated strains such as isozyme and protein patterns as well
as restriction fragment length polymorphisms (RFLPs) and DNA fingerprinting
have proven to be a very reliable approach to accurate strainal characterization
(Bernier et al. 1983, Jeng and Hubbes 1983, Bates et al. 1989, Jeng et al. 1991,
Hintz et al. 1991).
These methods also provide a better view into the genome (all the genes carried
by a haploid germ cell) of the pathogen than earlier methods. For example, Jeng et
al. (1991) showed that the size of the mitochondrial genome was 40% larger for
the non-aggressive isolates than for the aggressive ones. The restriction site map
of the mitochondrial genome which is a diagram portraying a linear array of sites
on the DNA segment at which specific enzymes cleave the molecule, showed that
the various isolate groups differed from each other by discrete length mutations in
their mitochondrial genome (Hintz et al. 1991). Based on the above criteria and
some physiological characters, Brasier (1991) separated the aggressive sub-group
from the non-aggressive one by classifying the former as a new species, which he
named O. novo-ulmi, while the non-aggressive group maintained the name O.
ulmi. Further investigations by Jeng et al. (1996) showed that the DNA sequence
of the ITS1 and ITS2 region of the ribosomal gene of the aggressive and nonaggressive group display high homology but differ between each other in one DNA
base pair showing the close relatedness of the two groups. The ribosomal gene is
a very important genetic marker. It is highly conserved, stable and shows little
change over long time periods. However some of its regions (DNA stretches) such
as those known as internal spacers (ITS) show some variation while others known
as 18S, 5.8S, or 26-28S are very stable. Both are used for characterization of
taxonomic units. Lately Brasier and Mehrotra (1995) described a third species
belonging to the Ophiostoma group: O. himal-ulmi. This species has been found
on U. wallichiana in the Himalayas and lead to the hypothesis that the DED may
have its origin in this relatively narrow geographic region.
Methods of molecular biology such as RFLPs of mitochondrial DNA (mtDNA),
nuclear DNA fingerprinting and RFLPs of the ribosomal DNA (rDNA) are very
sensitive tools not only for strainal characterization but also for monitoring
population dynamics. Studies of strains of O. ulmi population from Manitoba,
southeastern Saskatchewan and northern Dakota show that these populations are
composed of well defined fungal strains (Hintz et al. 1993, Hubbes 1992). This
observation is based on the restriction site pattern of the mtDNA. Analysis of the
nuclear DNA fingerprinting and rDNA reveal that the nuclear type of all isolates is
that of the aggressive sub-group (O. novo-ulmi) (Hubbes 1992). Mitochondrial
DNA in O. ulmi is inherited from the mother and the nuclear DNA from the father
(unpublished results from our laboratory). This means those strains carrying nonaggressive mitochondrial types and aggressive nuclear types resulted from a cross
between a non-aggressive mother (O. ulmi) and an aggressive father. Such strains
have been reported for Manitoba (Hubbes 1992). Very recently Brasier et al.
(1998) found similar strains in Europe. These observations are of great importance
for the selection and breeding strategies which attempt to develop elms that in
future can tolerate the disease like Siberian elms. It further indicates that under
North American field conditions the number of strains is rather limited, a fact that
has also been found by Brasier (1996). Changes in non-aggressive and
aggressive subgroups within two populations of American elm in New England has
also been reported by Houston (1991), a fact already known from Europe (Brasier
1991). The population of the non-aggressive subgroup is declining.
Furthermore, spore deficient strains of O. ulmi have been successfully isolated;
these natural mutants lack the ability to produce conidiospores, blastospores, and
ascospores. As a result of these mutants, O. ulmi is incapable of causing internal
and external disease symptoms normally associated with DED (Richards et al.
1982, Richards, 1993, 1994, 1998). Spore production is of insturmental importance
for the pathogen for transmittance by the elm bark beetle vector and rapid
distribution within the elms vascular system. Understanding the mechanism(s) that
block O. ulmi sporulation may be very helpful in developing methods of DED
control.
Fungal metabolites as factors of virulence
Although the aggressiveness of O. ulmi strains was initially established by
inoculation experiments, the basis of this ability has not yet been precisely
determined. Knowing these factors precisely would allow effective DED control
strategies including the development and selection of long term disease tolerant
American elms. Brasier and Gibbs (1976) have shown in crossing and subsequent
inoculation experiments, that the F1 generation of the fungus does not exceed the
virulence of their parents. Assumptions (based on circumstantial evidence) have
been made that toxins, such as cerato ulmin (CU) (Takai 1980, Richards 1993),
peptidorhamno-mannan (Claydon et al. 1980, Nordin and Storbel 1981, Scheffer
1983, Scheffer et al. 1987), glycopeptides and glycoprotein elicitors (Yang et al.
1989, Hubbes 1993) may function as factors of virulence. Binz and Canevascini
(1996) stated that production of extra-cellular laccase may be important for the
survival of the fungus in its host. Confirmation of these compounds as factors of
virulence is still waiting. For example, experiments by Bernier (1988) did not
confirm previous results by Takai (1980) showing a correlation between high CU
production and virulence. It appeared that the only way to prove the role of CU as
a key factor of virulence would be the production of a number of mutants that are
unable to produce the CU toxin. These CU negative mutants (CU-) should not be
able to cause DED when inoculated into elms. If they do, then CU is not a major
virulence factor.
Bernier (1988) produced a large number of chemical induced mutants, but none
were CU-. The problem with chemically induced mutants is that the fungal genome
may be altered at many more sites than those phenotypically visible. This led to
efforts to identify and isolate the genes responsible for CU production (Yaguchi et
al. 1993, Bowden et al. 1994, Jeng et al. 1996). Once the CU gene had been
isolated a CU- mutant was created by transformation-mediated gene disruption of
an aggressive strain (O. novo-ulmi). Bioassay of the CU- strain in highly
susceptible elm trees indicated no difference in percent of brown streaks under the
bark and percent foliar wilting. Simultaneously Tegli and Scala (1996) obtained five
CU- mutants by UV-irradiation. In their inoculation experiments two out of the five
mutants showed significant reduction in pathogenicity when compared to the wild
type. However, very likely the UV-treatment affected not only genes of the CU
pathway but also a number of other genes sitting at important metabolic switching
points not detected by the authors.
CU- strains do occur naturally and are pathogenic (Brasier et al. 1994). This
would support the view that CU is not a major virulence factor. However there
exists another possibility, i.e., that the gene(s) for pathogen virulence and CU
production are located close to each other giving the impression of one single unit.
The loss of one during reproduction or by mutation would not affect the expression
of the other. Recent studies by Scala et al. (1997) found higher CU levels in wilting
leaves of elm seedling infected with aggressive isolates (O. novo-ulmi) than in
those leaves of seedlings infected with non-aggressive strains (O. ulmi). Temple
(1997) found that a transformed non-aggressive strain, which over expresses CU
production showed no alteration in virulence when compared to the parent strain.
Unfortunately no experiments were conducted to test whether the CU gene of the
aggressive strain was expressing the correct CU protein in vivo, as tested by Scala
et al (1997). CU research is complicated with various conflicting results being
obtained by different scientists. CU may one day be shown to be a major factor in
pathogen fitness and virulence.
Virus-like RNA elements for the control of DED
In the mean time (Brasier 1983, 1986, Hoch et al. 1985, Rogers et al. 1986,
Brasier et al. 1993, Webber 1987, 1993) described the occurrence of double
stranded ribosomal nucleic acid (dsRNA) particles in isolates of the aggressive
strains (O. novo ulmi) and non-aggressive strains, and termed them as d-factors.
One of them, the d2 factor, has been associated with reduced vigor in infected
isolates (Hong et al. 1998). Work in Brasier’s laboratory has been conducted to
use the d-factor to control Dutch elm disease on a wide scale (Sutherland and
Brasier 1997). The problem up to now has been that the d-factor is not easily
transmitted from strain to strain, because not all strains are vegetatively
compatible. Furthermore, the transformation of the fungus into the yeast phase,
one of the main distribution phases of the fungus within the tree (Banfield 1941,
Pomerleau and Mehran 1966, Pomerleau 1968) allows Ophiostoma individuals to
lose deleterious d-factors (Webber 1993). Similar problems have been
encountered in the US with hypovirulent strains of Cryphonectria parasitica, the
causal agent of chestnut blight (Choi and Nuss 1992, Enebak et al. 1994).
However recent investigations suggest that it is the effect of induced resistance
triggered by the hypovirulent strain that is responsible for the survival of chestnuts
infected by chestnut blight (Schafleitner and Wilhelm 1997, Ghabrial 1998).
Apparently the transformation of virulent strains to hypo-virulent strains induces
some changes in the physiology of hypo-virulent strains that affect the pathogen
and mobilize effective defense reactions in the chestnut host.
Induced resistance for DED control
Our efforts here in Toronto concentrated on the defense mechanisms of elms in
response to fungal infection. Cross-protection against aggressive strains of O. ulmi
was reported in U. hollandica and U. americana (Scheffer et al. 1980, Hubbes and
Jeng 1981). Seedlings of U. americana were indeed protected against the attack
by aggressive strains when first inoculated with non-aggressive strains (Jeng et al.
1983, Duchesne 1985, Duchesne et al. 1986, Sutherland et al. 1995). We have
isolated and identified a number of chemicals produced by the elm in response to
the inoculations as mansonones A, C, D, E, F and G from fungal inhibitory
sapwood extract of elm seedlings treated with O. ulmi (Dumas et al. 1983, 1986
Jeng et al. 1983). Procter and Smalley (1988) also observed increased
mansonone accumulation in elm inoculated with O. ulmi strains. Wu et al. (1989)
demonstrated the toxic effect of these chemicals on the physiology and ultrastructure of the fungus. Mansonones were first reported to accumulate in elms
infected with O. ulmi by Elgersma and Overeem (1971). However, these authors
were unable to correlate mansonone accumulation with resistance to DED. There
are several reasons why these authors overlooked the correlation. For example
they compared mansonone content between treatments on the basis of number of
cuttings that were extracted rather than using a more precise unit of comparison
such as dry or fresh weight. Smalley et al. (1993) and Procter et al. (1994), using a
number of chemically induced mutants showing lower mansonone tolerance than
the parent strains, point out that mansonones alone do not play a major role in the
resistance of elms to DED. These authors could not correlate mansonone
sensitivity of a number of DED fungal mutants with high virulence. This is not
surprising since chemically induced mutants often are altered at many more loci
(position that a gene occupies in a chromosome) than those tested and visible.
Therefore correct interpretation of the results is very difficult without knowing all
the affected loci and their genetic stability.
Nevertheless, mansonone production is a very sensitive and precisely measurable
process implicated in the host’s reaction in response to pathogen invasion. It is
definitely a part of genetically programmed sequences of host defense
mechanisms in DED. Duchesne (1993) concluded that timing of expression of
different mechanisms of resistance to DED is critical for both anatomical and
chemical means of defense to be effective in localizing the pathogen. He bases his
assumption on the faster accumulation of mansonones in U. pumila (Duchesne et
al. 1985), the faster mansonone accumulation in U. americana inoculated with
aggressive isolates, and finally on the faster barrier zone formation (Shigo and
Tippet 1981) in non-host trees than in host trees inoculated with O. ulmi (Rioux
and Ouellette 1991a, b). To isolate the mansonone-inducing factor of the DED
fungus, a sensitive bioassay had to be developed. Szczegola-Derkacz (1988)
showed that tissue cultures responded to O. ulmi inoculations with mansonone
production. Autoclaved spores of the yeast phase of the DED fungus produced the
same effect as living spores indicating that the compounds triggering mansonone
production are heat stable. Yang et al. (1989) demonstrated that fungal culture
filtrates, cytoplasm and cell walls of O. ulmi contain molecules that elicit
mansonone accumulation in elm calli. The culture filtrate elicitor has been purified
(Yang 1991) and its structure identified (Hubbes et al. unpublished results).
When elm seedlings and elm trees (10 cm in diameter) were first injected with the
elicitor and then challenged with 8,000 to 1 million spores of an aggressive strain
per tree, the treated trees showed significant difference in wilting when compared
to the control. The 5-year old seedlings obtained the high spore dose, while the
trees obtained the lower dose (unpublished results). A United States patent
application based on the structure of the elicitor for the control of DED has been
filed. The elicitor can be injected in liquid form or in pellet form into the tree. It is
heat stable, has an indefinite shelf life, appears environmentally safe and easy to
administer into the tree, particularly in pellet form. Field trials on the feasibility of
pellet treatment as well as elicitor activity have been conducted in 1997 by a
number of cities in Manitoba, Saskatchewan and Alberta. Field trials on the
efficacy of the elicitor are presently being repeated in Ontario, Saskatchewan and
Alberta. Investigations in our Forest Pathology laboratory on the mechanisms of
induced resistance show that they follow similar complex defense reactions as
those found in agricultural crops (Somssich and Hahlbrock 1998). The elicitor
induces a chain of defense reactions that prevent the rapid spread of the fungus.
However the difference between agricultural crops and elm trees is that elm trees
are wild type individuals with greater genetic variability and therefore show greater
variations in their defense reactions. Hence, control of fungal pathogens in trees
by induced resistance is a new approach of disease control and appears to be one
of the few remaining options to protect the existing elm populations in our
communities against DED.
Since the first appearance of DED a nagging question has emerged over and over:
“Is the elm tree worth saving, and will this tree follow the doomed fate of the North
American sweet chestnut? The chestnut has lost its once vast territories and other
tree species have taken its place. Why then worry about losing another native tree
species?” The very emotional argument against such a statement is that although
the North American continent is rich in number, variety and magnificence of native
trees, no tree can replace the American elm in the hearts of the people. The
argument goes further in that the elm typifies, as no other tree does, the finest
things in North American life. No substitute greenery, however luxurious, could
hide the scars that would be left by the loss of the elm in our cities.
Acknowledgements
Part of our work has been supported by NSERC, City of Winnipeg, Province of
Manitoba, Province of Saskatchewan, Coalition to Save the Elms, University of
Toronto. Many thanks also to Mike Allen, Chief Forester of the City of Winnipeg,
for reviewing the manuscript.
References
Banfield, W.M. 1941. Distribution by the sap stream of spores of three fungi
that induce vascular wilt disease of elm. J. Agic. Res. 62(11):637-681.
Bates, M.R., K.W., Buck and C.M. Brasier. 1989. The use of nuclear and
mitochondrial DNA polymorphisms to investigate the population genetics,
epidemiology and evolution of Ophiostoma ulmi - the causative agent of
Dutch elm disease. J. Cell. Bioch. 13:112.
Bernier, L. 1983. Relationships between isoenzymes, cultural characters,
and pathogenicity in Ceratocystis ulmi (Busim.) C. Moreau. M.Sc.F. thesis,
Department of Forestry, University of Toronto.
Bernier, L. 1988. Induction, characterization and mapping of mutations in
Ophiostoma ulmi, the causal agent of Dutch elm disease. Ph.D. thesis,
Department of Forestry, University of Toronto.
Bernier, L. and M. Hubbes. 1990a. Mutations in Ophiostoma ulmi induced by
N-methyl-N'-nitro-N-nitrosoguanidine. Can. J. Bot. 68:225-231.
Bernier, L. and M. Hubbes. 1990b. Meiotic analysis of induced mutations in
Ophiostoma ulmi. Can. J. Bot. 68:232-235.
Bernier L., R.S. Jeng and M. Hubbes. 1983. Differentiation of aggressive
and non•aggressive strains of Ceratocystis ulmi by polyacrylamide gel
electrophoresis of intramycelial enzymes. Mycotaxon, 17: 456•472.
Bernier, L., D. Yang, G.B. Ouellette and M. Dessureault. 1996. Assessment
of Phaeotheca dimorphospora for biological control of the Dutch elm disease
pathogens, Ophiostoma ulmi and O. novo-ulmi. Plant Pathol. 45(4):
Binz, T. and G. Canevascini. 1996. Differential production of extracellular
laccase in the Dutch elm disease pathogens Ophiostoma ulmi and O. novoulmi. Mycol. Res. 100(9):1060-1064.
Birch, M.C., T.D. Paine and J.C. Miller. 1981. Effectiveness of pheromone
mass-trapped of the smaller European elm bark beetle. Calif. Agric. 35(1-2):67.
Bowden, C.G., W.E. Hintz, R. Jeng, M. Hubbes and P.A. Horgen. 1994.
Isolation and characterization of the Dutch elm disease pathogen,
Ophiostoma ulmi. Curr. Genet. 25:323-329.
Brasier, C.M. 1977. Inheritance of pathogenicity and cultural characters in
Ceratocystis ulmi: Hybridization of protoperithecial and non•aggressive
strains. Trans. Brit. Mycolog. Soc. 68: 45•52.
Brasier, C.M. 1979. Dual origin of recent Dutch elm disease outbreaks in
Europe. Nature 281: 78•80
Brasier, C.M. 1982. Occurrence of three sub•groups with Ceratocystis ulmi.
p. 298•321. In: Proceedings of the Dutch elm disease symposium and
workshop, Winnipeg, Manitoba, October 5•9, 1981 (Eds. E.S. Kondo, Y.
Hiratsuka and W.B.G. Denyer) Manitoba Department of Natural Resources,
Manitoba, Canada.
Brasier, C.M. 1983. A cytoplasmically transmitted disease of Ceratocystis
ulmi. Nature 305:220-223.
Brasier, C.M. 1986. The d-factor in Ceratocystis ulmi: its biological
characteristics and implication for Dutch elm disease. p. 177-208. Fungal
Virology (Ed. K.W. Buck). CRC Press, Florida.
Brasier, C.M. 1988. Rapid changes in genetic structure of epidemic
populations of Ophiostoma ulmi. Nature 332:538-541.
Brasier, C.M. 1991. Ophiostoma novo-ulmi sp. nov., causative agent of
current Dutch elm disease pandemics. Mycopathologia 115:151-161.
Brasier, C.M. 1996. Low genetic diversity of Ophiostoma novo-ulmi
population in North America. Mycologia 88(6):951-964.
Brasier, C.M. and J.N. Gibbs. 1976. Inheritance of pathogenicity and cultural
characters in Ceratocystis ulmi: Hybridization of aggressive and non
•aggressive strains. Ann. Appl. Biol. 83: 31•37.
Brasier, C.M. and M.D. Mehrotra. 1995. Ophiostoma himal-ulmi sp. nov., a
new species of Dutch elm disease fungus endemic to the Himalayas. Mycol.
Res. 99(2):205-215.
Brasier, C.M., M.R. Bater, N.W. Charter and K.W. Buck. 1993. DNA
polymorphism, perithecial size and molecular aspects of D factors in
Ophiostoma ulmi and O. novo-ulmi. p. 308-321. In: Dutch Elm Disease
Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and J.L.
Sherald). Springer-Verlag, Berlin, New York.
Brasier, C.M., S. Kirk and S. Tegli. 1994. Naturally occurring non cerato-
ulmin producing mutants of Ophiostoma
novo-ulmi are
pathogenic but lack of aerial mycelium. Mycol. Res.
99:436-440.
Brasier, C.M., S.A. Kirk, N.D. Pipe and K.W. Buck. 1998. Rare interspecific
hybrids in natural populations of the Dutch elm disease pathogens
Ophiostoma ulmi and O. novo-ulmi. Mycol. Res. 102(1):45-57.
Campana, R.J. and R.J. Stipes. 1981. Dutch elm disease in North America with
particular reference to Canada: Success or failure of conventional control
methods. Can. J. Plant Pathol. 3:252-259.
Choi, G.H. and D.L. Nuss. 1992. Hypovirulence of chestnut blight fungus
conferred by an infectious viral cDNA. Science 257:800-803.
Claydon, N., D.M. Elgersma and J.F. Grove. 1980. The phytotoxicity of some
phenolic metabolic products of Ophiostoma ulmi to Ulmus species. Nether. J.
of Plant Pathol. 86:229-237.
Duchesne, L.C. 1985. Phytoalexin accumulation of resistance to Dutch elm
disease. M.Sc.F. thesis, Department of Forestry, University of Toronto. 111
pp.
Duchesne, L.C. 1993. Mechanisms of resistance: can they help save
susceptible elms? p. 239-254. In: Dutch Elm Disease Research: Cellular and
Molecular Approaches. (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag,
Berlin, New York
Duchesne, L.C., R.S. Jeng and M. Hubbes. 1985. Accumulation of
phytoalexins in Ulmus americana in response to injection by a non•aggressive
and an aggressive strain of Ophiostoma ulmi. Can. J. Bot. 63: 678•680.
Duchesne, L.C., M. Hubbes and R.S. Jeng. 1986. Mansonone E and F
accumulation in Ulmus pumila resistant to Dutch elm disease. Can. J. For. Res.
16:410•412
Dumas, M.T., G.M. Strunz, M. Hubbes and R.S. Jeng. 1983. Isolation and
identification of six mansonones form Ulmus americana infected with
Ceratocystis ulmi. Experientia 39:1089•1090.
Dumas, M.T., G.M. Strunz, M. Hubbes, and R.S. Jeng. 1986. Inhibition of
Ceratocystis ulmi by mansonones A, C, D, F, and G isolated from Ulmus
americana. Europ. J. For. Path. 16:217•222.
Elgersma, D.M. and J.C. Overeem. 1971. The relation of mansonones to
resistance against Dutch elm disease and their accumulation as induced by
several agents. Neth. J. Plant Pathol. 79:218-220.
Enebak, S.A., W.L. MacDonald, and B.I. Hillman. 1994. Effect of dsRNA
associated with isolates of Cryphonectria parasitica from the central
Appalachians and their relatedness to other dsRNAs from North America and
Europe. Phytopathology 84:528-534.
Ghabrial, S.A. 1998. Origin, adaptation and evolutionary pathways of fungal
viruses. Virus Genes 16(1):119-131.
Gibbs, J.N. 1981. Dutch
elm disease. p. 7. In:
Compendium of elm diseases (Eds. R.J. Stipes and
R.J. Campana). Am. Phytopathol. Soc. St. Paul, MN.
Gibbs J.N. and C.M. Brasier. 1973. Correlation between cultural characters and
pathogenicity in Ceratocystis ulmi isolates form Britain, Europe and North
America. Nature 241:381•383.
Gibbs, J.N., H.M. Heybroek and F.W. Holmes. 1972. Aggressive strain of
Ceratocystis ulmi in Britain. Nature 236:121-122.
Heybroek, H.M. 1983. Resistant elms for Europe. p. 108-113. In: Research on
Dutch elm disease in Europe (Ed. A. Burdekin). Forestry Commission Bull. 60,
London.
Heybroek, H.M. 1993. Why bother about the elm? p. 1-8. In: Dutch Elm
Disease Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen
and J.L. Sherald). Springer-Verlag, Berlin, New York.
Hintz, W.E., R.S. Jeng, M. Hubbes and P.A. Horgen. 1991. Three populations
of Ophiostoma ulmi (aggressive subgroup) as uncovered by mitochondrial DNA
restriction-site mapping and nuclear DNA fingerprinting. Exp. Mycol. 15:316325.
Hintz, W.E., R.S. Jeng, M. Hubbes and P.A. Horgen. 1993. A genetic survey
of the pathogen fungus Ophiostoma ulmi at a Dutch elm disease front in
western Canada. Genome 36:418-426.
Hoch, J.G., S.M. Tavantzis, R.J. Campana and S.L. Anagnostakis. 1985.
Evaluation of the presence of double-stranded RNA in Ceratocystis ulmi.
Can. J. Bot. 63:297-300.
Holmes, F.W. 1976. While Dutch elm disease continues to spread, natural
selection in wild elms may save the species from extinction. Horticulture
54(1):72-78.
Holmes, F.W. and D.F. Plourde. 1982. Use of Pseudomonas syringae in
naturally infected elms along streets. In: Proceedings of the Dutch elm
disease symposium and workshop, Winnipeg, Manitoba, October 5•9, 1981
(Eds. E.S. Kondo, Y. Hiratsuka and W.B.G. Denyer). pp. 62•70. Manitoba
Department of Natural Resources, Manitoba, Canada.
Hong, Y.G., T.E. Cole, C.M. Brasier and K.W. Buck. 1998. Novel structures
of two virus-like RNA elements from a diseased isolate of the Dutch elm
disease fungus, Ophiostoma novo-ulmi. Virology 242:80-89.
Houston, D.R. 1991. Changes in nonaggressive and aggressive subgroups
of Ophiostoma ulmi within two populations of American elm in New England.
Plant Dis. 75(7):720-722.
Hubbes, M. 1981. Discussion. p. 258-259. In: Dutch elm disease in North America
with particular reference to Canada: Success or failure of conventional control
methods (R.J. Campana and R.J. Stipes). Can. J. Plant Pathol. 3:252-259.
Hubbes, M. 1992. Identification of wild type isolates of Ophiostoma ulmi from
Manitoba by mitochondrial DNA restriction fragment length polymorphisms and
ribosomal DNA patterns. Report submitted to Manitoba Natural Resources.
Hubbes, M. 1993. Mansonones, elicitors and virulence. p. 208-215. In: Dutch Elm
Disease Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and
J.L. Sherald). Springer-Verlag, Berlin, New York.
Hubbes, M. and R.S. Jeng. 1981. Aggressiveness of Ceratocystis ulmi strains and
induction of resistance in Ulmus americana. Europ. J. For. Path. 11:257•264.
Huntley, G.D. 1982 The elm – a resurgent resource or a persistent problem?
p. 103•111 In: Proceedings of the Dutch elm disease symposium and
Hiratsuka and W.B.G. Denyer) . Manitoba Department of Natural Resources,
Manitoba, Canada.
Jeng R.S. and M. Hubbes. 1983. Identification of aggressive and non•aggressive
strains of Ceratocystis ulmi by polyacrylamide gradient gel electrophoresis of
intramycelial proteins. Mycotaxon, 17:445•455.
Jeng, R.S., A.C. Alfenas, M. Hubbes and M. Dumas. 1983. Presence and
accumulation of fungitoxic substances against Ceratocystic ulmi in Ulmus
americana: possible relation to induced resistance. Europ. J. For. Path. 13:261
•178.
Jeng, R.S., L.C. Duchesne, M. Sabourin and M. Hubbes. 1991. Mitochondrial
DNAs restriction fragment length polymorphisms of aggressive and nonaggressive isolates of Ophiostoma ulmi. Mycol. Res. 95(5):537-542.
Jeng, R.S., W.E. Hintz, C.G. Bowden, P.A. Horgen and M. Hubbes. 1996. A
comparison of the nucleotide sequence of the cerato-ulmin gene between
aggressive and non-aggressive isolates of Ophiostoma ulmi sensu lato, the causal
agent of Dutch elm disease. Current Genetics 29(2):168-173
Jin, H., G.R.B. Webster, N.J. Holliday, P.A. Pines, and A.R. Westwood. 1996.
An elm bark beetle bioassay for residual efficacy of chlorpyrifos and
cypermethrin used for the control of Dutch elm disease in Manitoba. J. Environ.
Sci. Health Part B 31(4):751-761.
Kondo, E.S. 1978. Scope and limitations of carbendazim phosphate injections in
Dutch elm disease control. J. Arboric. 4:86-88.
Kondo, E.S., D.N. Roy and E. Jorgensen. 1973. Salts of methyl-2-benzimidazole
carbamate (MBC) and assessment of their potential in Dutch elm disease control.
Can. J. For. Res. 3:548-555.
Lanier, G.N. 1978. Vectors. p. 13-17. In: Dutch elm disease: perspectives after 60
years (Eds. W.A. Sinclair and R.J. Campana). Cornell Univ. Agric. Exp. Stn.
Search (Agriculture) 8.
Lanier, G.N. 1989. Trap trees for control of Dutch elm disease. J. Arboric. 15:105111.
Lanier, G.N. and J.W. Peacock. 1981. Vectors
of the pathogen. p.
14-16. In: Compendium of elm diseases (Eds. R.J.
Stipes and R.J. Campana). Am. Phytopathol. Soc. St.
Paul, MN.
Lester, D.T. 1978. Control tactics in research and practice: V. Exploiting host
variation. p. 39-42. In: Dutch elm disease: perspectives after 60 years (Eds. W.A.
Sinclair and R.J. Campana). Cornell Univ. Agric. Exp. Stn. Search (Agriculture) 8.
Mazzone, H.M, J. Kluck, N.R. Dubois and R. Zerilll. 1982. Dutch elm disease
control with biological agents or their metabolites. p. 36•45. In: Proceedings of the
Dutch elm disease symposium and workshop, Winnipeg, Manitoba, October 5•9,
1981 (Eds. E.S. Kondo, Y. Hiratsuka and W.B.G. Denyer). Manitoba Department
of Natural Resources, Manitoba, Canada.
Nordin, J.H. and G.A. Strobel. 1981. Structural and immunochemical studies on
the phytotoxic peptidorhamnomannan of Ceratocystis ulmi. Plant Physiol. 12081213.
O'Callaghan, D.P. and C.P. Fairhurst. 1983. Evaluation of the trap tree technique
for the control of Dutch elm disease in northwest England. p. 23-28. In: Research
on Dutch elm disease in Europe (Ed. D.A. Burekin). Forestry Commission Bull. 60,
London.
Ouellette, C.E. and R. Pomerleau. 1965. Recherches sur la Résistance de L'Orme
D'Amérique au Ceratocystis ulmi. Can. J. Bot. 43:85-97.
Parker, K.G., D.L. Collins, L.J. Tyler, D.P. Connola, W.E. Ozard and H.
Dietrich. 1947. The Dutch elm disease – association of Ceratostomella ulmi
with Scolytus multistriatus, its advance into new areas, and control of the
disease. Cornell Univ. Agr. Exp. Stn. Memoir 275. 44 pp.
Pomerleau, R. 1965. Seasonal transmission of the elm disease by
Hylurgopinus rufipes in Quebec. Can. J. Bot. 43:1592-1595.
Pomerleau, R. 1968. Progression et localisation de l'infection par le Ceratocystis
ulmi dans l'orme d'Amérique. Phytopath. Z. 63:301-327.
Pomerleau, R. 1981. Dutch elm disease in Canada. p. 8-9. In: Compendium of elm
diseases (Eds. R.J. Stipes and R.J. Campana). Am. Phytopathol. Soc. St. Paul,
MN.
Pomerleau, R. and R. Mehran. 1966. Distribution of spores of Ceratocystis
ulmi labelled with phosphorus-32 in green shoots and leaves of Ulmus
americana. Naturaliste Can. 93:577-582.
Procter, R.H. and E.B. Smalley. 1988. Localized accumulation of
mansonones E and F in elms following inoculations with Ophiostoma ulmi.
Can. J. Plant Pathol. 10:371 (Abstract).
Proctor, R.H., R.P. Guries and E.B. Smalley. 1994. Lack of association
between tolerance to the elm phytoalexin mansonone E and virulence in
Ophiostoma novo-ulmi. Can. J. Bot. 72:1355-1364.
Prosser, T. 1998. One company’s success against Dutch elm disease. Tree
Care Industry June 1998:60-64.
Richards, W.C. 1993. Cerato-ulmin: A unique wilt toxin of instrumental
significance in the development of Dutch elm disease. p. 89-151. In:
Dutch
Elm Disease Research: Cellular and Molecular
Approaches. (Eds. M.B. Sticklen and J.L. Sherald).
Springer-Verlag, Berlin, New York.
Richards, W.C. 1994. Nonsporulation in the Dutch elm disease fungus,
Ophiostoma ulmi: evidence for control by a single
nuclear gene. Can. J. Bot. 72:461-467.
Richards, W.C. 1998. Novel spore deficient mutants of the dimorphic fungal
plant pathogen, Ophiostoma
ulmi. Crop Health
Unlimited Horizons. CPS/APS joint meeting, July 67/97. Winnipeg, Manitoba. Phytopathology 88: No
9 (Supplement), 1998 S113.
Richards, W.C., S. Takai, D. Lin, Y. Hiratsuka and S. Asina. 1982. An
abnormal strain of Ceratocystis ulmi incapable of producing external
symptoms of Dutch elm disease. Europ. J. For. Path. 12:193•202.
Rioux, D. and G.B. Ouellette. 1991a. Barrier zone formation in host and non-host
trees inoculation with Ophiostoma ulmi. 1. Anatomy and Histochemistry. Can. J.
Bot. 69:2055-2073.
Rioux, D. and G.B. Ouellette. 1991b. Barrier zone formation in host and non-host
trees inoculation with Ophiostoma ulmi. 2. Ultrastructure. Can. J. Bot. 69:20742083.
Rogers, H.J., K.W. Buck and C.M. Brasier. 1986. Transmission of doublestranded RNA and a disease factor in Ophiostoma ulmi. Plant Pathol.
35:277-287.
Roy, D.N., J.R. Purdy and P. Ayyamperumal. 1980. Distribution of methyl
benzimidazol-2-yl carbamate phosphate in elm: effects of chemical properties and
formulation variables. Can. J. For. Res. 10:143-151.
Roy, D.N., J.R. Purdy, P.A. Perumal and J.K. Grace. 1988. Effect of application
equipment on the distribution of chlorpyrifos applied for Dutch elm disease vector
control. Proc. Entomo. Soc. Ont. 119:63-68.
Scala, A., M. Pattuelli, L. Coppola, M. Guastini, S. Tegli, G. DelSorbo, L.
Mittempergher and F. Scala. 1997. Dutch elm disease progression and
quantitative determination of cerato-ulmin in leaves, stems and branches of
elms inoculated with Ophiostoma novo-ulmi and O. ulmi. Physiol. Mol. Plant
Pathol. 50:349-360.
Schafleitner, R. and E. Wilhelm. 1997. Effect of virulent and hypovirulent
Cryphonectria parasitica (Murr.) Barr on the intercellular pathogen related
proteins and on total protein pattern of chestnut (Castanea sativa Mill.).
Physiol. Mol. Plant Pathol. 51:323-332.
Scheffer, R.J. 1983. Toxins in Dutch elm disease. p. 82-85. In: Research on Dutch
elm disease in Europe (Ed. D.A. Burekin). Forestry Commission Bull. 60, London.
Scheffer, R.J., H.M. Heybroek and D.M. Elgersma. 1980. Symptom expression in
elms after inoculation with combinations of an aggressive and non-aggressive
strain of Ophiostoma ulmi. Neth. J. Pl. Pathol. 86:315-317.
Scheffer, R.J., J.I. Liem and D.M. Elgersma. 1987. Production in vitro of
phytotoxic compounds by non-aggressive and aggressive isolates of
Ophiostoma ulmi, the Dutch elm disease pathogen.
Physiol. Molec. Pl. Path. 30:321-325.
Scheffer, R.J., A.C. Brakenhoff, A. Kerkenaar and D.M. Elgersma. 1988. Control of
Dutch elm disease by the sterol biosynthesis inhibitors fenpropimorph and
fenpropidin. Neth. J. Pl. Path. 94:161-173.
Schreiber, L.R. 1993. An old problem; a new approach. p. 51-59. In: Dutch Elm
Disease Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and
J.L. Sherald). Springer-Verlag, Berlin, New York.
Schreiber, L.R. and A.M. Townsend. 1976. Variability in aggressiveness, recovery
and cultural characteristics of isolates of Ceratocystis ulmi. Phytopath. 66: 239
•244.
Sherald, J. 1993. Demands and opportunities for selecting disease resistant elms.
p. 60-68. In:
Dutch Elm Disease Research: Cellular and
Molecular Approaches. (Eds. M.B. Sticklen and J.L.
Shi, J.L. and C.M. Brasier. 1986. Experiments on the control of Dutch elm disease
by injection of Pseudomonas species. Eur. J. For. Path. 16:280-292.
Shigo, A.L. and R. Campana. 1977. Discoloured and decayed wood
associated with injection wounds in American elm. J. Arboric. 3:230-235.
Shigo. A.L. and J.T. Tippet. 1981. Compartmentalization of American elm tissues
infected by Ceratocystis ulmi. Plant Disease 65:715-718.
Smalley, E.B. 1978. Control tactics in research and practices: IV. Systemic
chemical treatments of trees for protection and therapy. p. 34-39. In: Dutch elm
disease: perspectives after 60 years (Eds. W.A. Sinclair and R.J. Campana).
Cornell Univ. Agric. Exp. Stn. Search (Agriculture) 8.
Dutch
elm disease. Annu. Rev. Phytopathol. 31:325-352.
Smalley, E.B. and R.P. Guries. 1993. Breeding elms for resistance to
Smalley, E.B., R.P. Guries and D.T. Lester. 1993. American liberty elms and
beyond: going from the impossible to the difficult. p. 26-45. In: Dutch Elm Disease
Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and J.L.
Smalley, E.B., K.F. Raffa, R.H. Proctor and K.D. Klepzig. 1993. Tree
responses to infection by species of Ophiostoma and Ceratocystis. p. 207218. In: Ceratocystis and Ophiostoma, Taxonomy, ecology, and
pathogenicity (Eds. M.J. Wingfield, K.A. Seifert and J.F. Webber). APS, St.
Paul, Minnesota.
Somssich, I.E. and K. Hahlbrock. 1998. Pathogen defence in plants - a
paradigm of biological complexity. Trends Plant Sci. 3(3):86-90.
Stennes, M.A. and D.W. French. 1987. Distribution and retention of thiabendazoic
hypophosphite and carbendazim phosphate injected into mature American elms.
Phytopath. 77:707-712.
Sticklen, M.B., M.G. Bolyard, R.K. Hajela and L.C. Duchesne. 1991. Molecular and
cellular aspects of Dutch elm disease. Phytoprotection 72:1-13.
Stipes R.J. and R.J. Campana. 1981. Compendium of elm disease. Amer.
Phytopathol. Soc., St. Paul. MN.
Strobel, G.A. and D. Myers. 1982. Bacterial antagonism as a strategy for the
treatment of Dutch elm disease. p. 46•61. In: Proceedings of the Dutch elm
disease symposium and workshop, Winnipeg, Manitoba, October 5•9, 1981 (Eds.
E.S. Kondo, Y. Hiratsuka and W.B.G. Denyer). Manitoba Department of Natural
Resources, Manitoba, Canada.
Sutherland, M.L. and C.M. Brasier. 1997. A comparison of thirteen d-factors
as potential biological control agents of Ophiostoma novo-ulmi. Plant Pathol.
46:680-693.
Sutherland , M.L., L. Mittempergher and C.M. Brasier. 1995. Control of Dutch
elm disease by induced host resistance. Eur. J. For. Path. 25:307-318.
Szczegola-Derkacz, M. 1988. Induction of mansonones by Ophiostoma ulmi in
tissue cultures of Ulmus americana and Ulmus pumila. M.Sc.F. thesis, Department
of Forestry, University of Toronto.
Takai, S. 1980. Relationship of the production of the toxin, cerato•ulmin, to
synnemata formation, pathogenicity, mycelial habit, and growth of Ceratocystis
ulmi isolates. Can. J. Bot. 58: 658•662.
Tegli, S. and A. Scala. 1996. Isolation and characterization of non-cerato-ulmin
producing laboratory induced mutants of Ophiostoma novo-ulmi. Mycol. Res.
100(6):661-668.
Temple, B.O. 1997. The biological role of the hydrophobin cerato-ulmin in the
life history of Ophiostoma ulmi and O. novo-ulmi. M.Sc.F.
thesis,
Department of Botany, University of Toronto. 133 pp.
Tomalak. M., H.E. Welch and T.D. Galloway. 1989. Nematode parasites of bark
beetles (Scolytidae) in southern Manitoba, with descriptions of three new species
of Sulphuretylenchus Rühm (Nematoda: Allantonematidae). Can. J. Zool. 67:24972505.
Townsend, A.M.and F.S. Santamour, Jr. 1993. Progress in the development of
disease-resistant elms. p. 46-50. In:
Dutch elm disease
research: Cellular and molecular approaches (Eds.
M.B. Sticklen and J.L. Sherald). Springer-Verlag
New York, Inc.
Ware, G. and F. Miller. 1997. Developing better elms. American Nurseryman
August 15, 1997:44-51.
Webber, J.F. 1987. Influence of the d2 factor on survival and infection by the Dutch
elm disease pathogen Ophiostoma ulmi. Plant Path. 36:531-538.
Webber, J.F. 1990. Relative effectiveness of Scolytus scolytus, S. multistriatus
and S. kirschi as vectors of Dutch elm disease. Eur. J. For. Pathol. 20:184-192.
Webber, J.F. 1993. D factors and their potential for the control of Dutch elm
disease. p. 322-332. In: Dutch elm disease research: Cellular and molecular
approaches (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag New York,
Inc.
Westwood, A.R. 1991. A cost between analysis of Manitoba’s integrated Dutch
elm disease management program 1975-1990. Proc. Entomol. Soc. Manitoba
47:44-59.
White, J.C. 1982. An industrial approach to biological control of Dutch elm
disease. p. 71•77. In: Proceedings of the Dutch elm disease symposium and
Hiratsuka and W.B.G. Denyer). Manitoba Department of Natural Resources,
Manitoba, Canada.
Wu, W.D., R.S. Jeng and M. Hubbes. 1989. Toxic effect of elm phytoalexin
mansonones on Ophiostoma ulmi, the causal agent of Dutch elm disease. Europ.
J. For. Path. 19:343-357.
Yaguchi, M., M. Pusztai-Carey, C. Roy, W.K. Surewicz, P.R. Carey, K.J.
Stevenson, W.C. Richards and S. Takai. 1993. Amino acid sequence and
spectroscopic studies of Dutch elm disease toxin, cerato-ulmin. p. 152-170. In:
Dutch elm disease research: Cellular and molecular approaches (Eds. M.B.
Sticklen and J.L. Sherald). Springer-Verlag New York, Inc.
Yang, D. 1991. Isolation, identification and characterization of phytoalexin elicitors
from Ophiostoma ulmi. Ph.D. thesis, Department of Forestry, University of Toronto.
Yang, D., R.S. Jeng and M. Hubbes. 1989. Mansonone accumulation in elm callus
induced by elicitors of Ophiostoma ulmi, and general properties of elicitors. Can. J.
Bot. 67:3490-3497.
Copyright
Elmcare Suggestion Box
Home > Suggestions
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
We are constantly looking for new ideas to improve this site. If you think we're
missing something that should be here, let us know. Work with us to create the
comprehensive elm tree website!
Email Address
Elm Tree Links
Quick Elm Facts
Suggestion
Send!
Copyright
http://www.elmcare.com/suggestions.htm [2/27/02 10:33:03 PM]
Contact the Webmaster
Home > Contact the Webmaster
How Trees Work
Found a bug? A broken link? Have any
suggestions to improve the site? Please send
it using the form below.
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
E-mail Address
Elm Tree Links
Quick Elm Facts
Comment
Submit
Reset
Thank you very much for your input!
Copyright
http://www.elmcare.com/contactwebmaster.htm [2/27/02 10:33:05 PM]
Elmcare.com - American Elm
Home > About Elms > Elm Species > American Elm
American Elm
How Trees Work
Ulmus americana L.
Height 35m (115')
About Elm Trees
Leaves 10-15cm (4-6")
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Copyright © APS (www.scisoc.org)
Quick Elm Facts
The American or White elm is the largest species of elm. Due to its graceful form
and size, it was an extremely popular urban tree before the spread of Dutch elm
disease. Once found mostly in eastern North America, remaining populations of
mature American elms are concentrated in the American Midwest and Canadian
Prairies.
If you are worried about Dutch elm disease, click here.
Copyright
http://www.elmcare.com/about_elms/species/species_american.htm [2/27/02 10:33:08 PM]
Elmcare.com - Rock Elm
Home > About Elms > Elm Species > Rock Elm
Rock Elm
How Trees Work
Ulmus thomasii Sarg.
Height 25m (80 feet)
About Elm Trees
Leaves 5-10cm (2-4 inches)
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
This elm species, also known as the cork elm due to corky ridges on branches, is
probably the least typical in form. Rather than branching out into large codominant limbs, the trunk remains distinct almost to the top of the tree. The crown
is cylindrical in shape and can grow to approximately 25m in height. A relatively
rare tree, it occurs mainly in the US Midwest. The leaves are 5-10 cm long and
hairy on the underside.
Copyright
http://www.elmcare.com/about_elms/species/species_rock.htm [2/27/02 10:33:10 PM]
http://www.elmcare.com/images/rockelm_leaves.jpg
http://www.elmcare.com/images/rockelm_leaves.jpg [2/27/02 10:33:11 PM]
http://www.elmcare.com/images/rockelm.jpg
http://www.elmcare.com/images/rockelm.jpg [2/27/02 10:33:13 PM]
Elmcare.com - Slippery Elm
Home > About Elms > Elm Species > Slippery Elm
Slippery Elm
How Trees Work
Ulmus rubra Muehl.
Height 40m (132')
About Elm Trees
Leaves 15-20cm (6-8")
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
The Slippery or Red elm is rather uncommon and lives mainly in the eastern half of
the US and southern Ontario and Quebec. The crown is umbrella-shaped with a
high canopy and the leaves are quite rough to the touch.
Elm Tree Links
Quick Elm Facts
Slippery elm is vulnerable to many of the same of the diseases as American elm
including Dutch elm disease and, as a result, rarely reach full maturity.
This tree has also been an important component of herbal medicine for more than
a century. Native Americans and early settlers used the dried inner portion of the
bark to soothe irritated stomachs and to heal wounds.
Copyright
http://www.elmcare.com/about_elms/species/species_slippery.htm [2/27/02 10:33:14 PM]
http://www.elmcare.com/images/slippery_leaves.jpg
http://www.elmcare.com/images/slippery_leaves.jpg [2/27/02 10:33:15 PM]
Elmcare.com - Scotch Elm
Home > About Elms > Elm Species > Scotch Elm
Scotch Elm
How Trees Work
Ulmus glabra Huds.
Height 40m (132')
About Elm Trees
Leaves 8-16cm (3-6")
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Also known as Wych elm, these trees are native to Europe and western Asia and
common in North and West Britain and Ireland. Similar to the Slippery elm, this
tree is often planted in urban centers in eastern North America. Often growing to a
height of 40m, 500 year-old specimens are known to exist.
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/species/species_scotch.htm [2/27/02 10:33:18 PM]
http://www.elmcare.com/images/scotch_leaf.jpg
http://www.elmcare.com/images/scotch_leaf.jpg [2/27/02 10:33:19 PM]
http://www.elmcare.com/images/scotch.jpg
http://www.elmcare.com/images/scotch.jpg [2/27/02 10:33:19 PM]
Elmcare.com - Camperdown Elm
Home > About Elms > Elm Species > Camperdown Elm
Camperdown Elm
How Trees Work
Ulmus glabra camperdownii
Height 3-5 m (10-15 feet)
About Elm Trees
Leaves 8-18 cm (3-7 inches)
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Also known as the Umbrella Elm or Weeping elm, this tree originated from a
seedling at Camperdown House, near Dundee Scotland. It is in fact a cultivar of
the Scotch elm.
Elm Tree Links
Quick Elm Facts
The leaves show a high degree of asymmetry at the base and are dark green in
colour. The drooping branches have made it attractive as a small-scale landscape
tree.
Copyright
http://www.elmcare.com/about_elms/species/species_camperdown.htm [2/27/02 10:33:21 PM]
http://www.elmcare.com/images/camperdown_leaf.jpg
http://www.elmcare.com/images/camperdown_leaf.jpg [2/27/02 10:33:22 PM]
http://www.elmcare.com/images/camperdown.jpg
http://www.elmcare.com/images/camperdown.jpg [2/27/02 10:33:23 PM]
Elmcare.com - Siberian Elm
Home > About Elms > Elm Species > Siberian Elm
Siberian Elm
Ulmus pumila L.
How Trees Work
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Copyright © APS (www.scisoc.org)
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
This medium-sized tree is native to northeastern Asia, but has been extensively
planted in cities across North America – especially in the West. This is due to the
Siberian elm’s resistance to Dutch elm disease and other pathogens.
The Siberian is extremely drought resistant. In grows at altitudes of up to 3900m
in Tibet and once grew in the Gobi desert. After the drought of the 1930’s in the
US Midwest, Siberian elms were planted extensively and became the most widely
planted shelterbelt tree in North America. It is now found in places as distant as
the USSR and Argentina where arid land came under cultivation.
Thriving on moist soils, this hardy tree can flourish in adverse conditions. Leaves
are narrow and between 2 and 7 cm long. Unlike other elm species, the leaves
are almost symmetrical at the base. The bark is gray and rough.
Many arborists consider the Siberian elm an undesirable street tree due to its
weak wood and prolific seeding.
Copyright
http://www.elmcare.com/about_elms/species/species_siberian.htm [2/27/02 10:33:25 PM]
Elmcare.com - English Elm
Home > About Elms > Elm Species > English Elm
English Elm
How Trees Work
Ulmus procera Salis.
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Copyright © APS
(www.scisoc.org)
This elm was relatively rare until the 17th and 18th centuries when it was planted
extensively by landowners along hedges that surrounded farmland. The leaves
are 6-9 cm long with a rough upper surface, and hairy underside.
Selected for their shade cover, genetic variation was reduced making the species
especially vulnerable to Dutch elm disease. After the disease reached Britain in
1967, more than 12 million English elms perished. Mature English elms can grow
to 36m and have narrow crowns.
Copyright
http://www.elmcare.com/about_elms/species/species_english.htm [2/27/02 10:33:27 PM]
http://www.elmcare.com/images/english_leaf.jpg
http://www.elmcare.com/images/english_leaf.jpg [2/27/02 10:33:28 PM]
http://www.elmcare.com/images/english_elm.jpg
http://www.elmcare.com/images/english_elm.jpg [2/27/02 10:33:29 PM]
Elmcare.com - Japanese Zelkova
Home > About Elms > Elm Species > Japanese Zelkova
Japanese Zelkova
How Trees Work
Zelkova serrata Thunb. Mak.
About Elm Trees
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Copyright © APS
Elm Tree Links
(www.scisoc.com)
Quick Elm Facts
Native to Japan, this medium-sized tree has the vase-shaped form typical of
American elms. Its tolerance of Dutch elm disease has made it a popular choice
to replace disease-stricken populations. It flourishes in almost any good soil
preferring a deep, well-drained moist loam.
Fast-growing, its leaves are slender and 3-5 cm long with 8-14 veins per side
ending in a single sharp tooth.
Copyright
http://www.elmcare.com/about_elms/species/species_japanese.htm [2/27/02 10:33:31 PM]
Elmcare.com - Winged Elm
Home > About Elms > Elm Species > Winged Elm
Winged Elm
How Trees Work
Ulmus alata
About Elm Trees
Leaves 4-8 cm (1.5 to 3 inches)
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
A small to medium-sized tree native to the southeastern U.S.
The bark is flat with scaly ridges separated by shallow, irregular furrows.
Copyright
http://www.elmcare.com/about_elms/species/species_winged.htm [2/27/02 10:33:33 PM]
http://www.elmcare.com/images/winged_leaves.jpg
http://www.elmcare.com/images/winged_leaves.jpg [2/27/02 10:33:33 PM]
Elmcare.com - Chinese Elm
Home > About Elms > Elm Species > Chinese Elm
Chinese Elm
How Trees Work
Ulmus parvifolia
About Elm Trees
Leaves 2-7 cm (0.8 to 2.5 inches)
The Elm Story
Identifying Elms
Elm Species
Biology of Elms
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Native to northern China, Japan, and Korea, the Chinese or Lacebark elm
generally has a broad, vase-like shape with pendulous branches. In warmer
regions, it may be evergreen. The bark is usually smooth. It grows fairly quickly
and is resistant to Dutch elm disease making it a popular choice for landscaping.
Quick Elm Facts
Copyright
http://www.elmcare.com/about_elms/species/species_chinese.htm [2/27/02 10:33:35 PM]
http://www.elmcare.com/images/chinese_leaf.jpg
http://www.elmcare.com/images/chinese_leaf.jpg [2/27/02 10:33:36 PM]
http://www.elmcare.com/images/chinese.jpg
http://www.elmcare.com/images/chinese.jpg [2/27/02 10:33:37 PM]
Elms in Winnipeg - Part 1
Home > Elms in Winnipeg March 2000 - Part 1
Part 1
How Trees Work
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Part 2
Part 3
Part 4
olseley Avenue wanders through a gentrified Winnipeg
neighbourhood on the north side of the Assiniboine River,
its 2.5 kilometres of sidewalk dappled by light that filters
through a canopy of American elms.
Sometimes the shady street follows the meandering
course of the muddy brown river; at other times, like
Portage Avenue just to the north, it obeys the
dictates of traffic engineers and straightens out. But
whether straight or curvaceous, it is always lined with
grand, old, century elms. Hundreds of them.
Back in the 1950s, when Winnipeggers began their passionate affair with the
automobile, if you wanted to avoid busy Portage Avenue on your way downtown or
if you lived in the south end and were on your way to see a Blue Bombers game at
the new Winnipeg Stadium, Wolseley was a fast alternate route with no
bothersome traffic lights or stop signs. It did, however, have an old tree growing
smack-dab in the middle of the road near the corner of Basswood Place. The
ancient Wolseley elm, according to local lore, was planted in 1859 by a girl named
Mary Anne Good who lived on a prairie farm near the bank of the Assiniboine.
Nearly 100 years later, by some road-planning oversight, it was still there, although
surrounded by a curb and a fringe of grass that Ripley's Believe It Or Not declared
was "the smallest park in the world." Motorists, however, were not amused, and
city officials worried that someone might drive into it and kill themselves.
Neighbourhood residents argued that the tree protected their kids from being killed
by speeding cars.
In September 1957, at the height of the football season, the city assigned a crew
to remove the offending elm. In the ensuing standoff, a dozen neighbourhood
women circled the tree, arm in arm, to fend off the buzz saws, and within minutes
the police had arrived, paddy wagons and all. A crowd gathered.
"If they want to chop down this tree," said one of the women, "they're going to have
to chop us down first."
http://www.elmcare.com/features/mar01-1.htm (1 of 2) [2/27/02 10:33:42 PM]
In the end, the matter was settled peaceably by newly-elected mayor Stephen
Juba, who pulled up in his Cadillac and sent the workers home. Most of the rest of
the neighbourhood's trees have also survived, somehow evading both the urbanplanners' axe and the more serious threat of Dutch Elm Disease. In fact, the city
remains shaded by a forest comprised of over 200,000 elms, a remarkable legacy
that is guarded by Winnipeggers every bit as vigilant as the defenders of the
Wolseley Elm. Their appreciation of the urban forest, and their decades-long battle
against a disease that has virtually extirpated the elm from the streets of most
other cities, is now finally offering some hope for those who might otherwise have
given up on what was once eastern North America's most popular city tree.
At the turn of the century, when the grain and railroad boom was fuelling
Winnipeg's growth, the city fathers looked south for inspiration and were, perhaps
inevitably, inspired by Chicago, a city with a similar economy, monumental
architecture, grand streets, and lots of elm trees. By then, much of eastern North
America had been cleared of forest, and city dwellers were starting to rethink the
value of trees. Arbour Day had become fashionable, and tree planters had only to
look to adjacent farmsteads, where the stubborn Ulmus americana, a very tough
tree for settlers to remove, still proliferated. The giant American elms that survived
the agricultural clearances and thrived on prime farmland became the source of
the graceful, parasol-shaped trees that would dominate the urban forests of North
America for decades to come.
Part 1
Part 2
Part 3
Part 4
Jamie Swift is a writer and broadcaster living in Kingston, Ontario. His most recent book, Wheel of
Fortune, was published in 1995. He is also the author of Cut and Run, a lament for the
mismanagement of Canadian forests.
Copyright
How Trees Work
Part 1
Part 2
Part 3
Part 4
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Winnipeg's early planners had a perfect source of planting
stock at hand. When the time came to bring trees into the
newly laid-out subdivisions on both sides of the Assiniboine
and Red rivers, they simply collected native elms from the
riverbanks. Each new city park featured a nursery where the
trees were grown to sapling size before being transplanted
along the generous boulevards. The city charged each
homeowner a lot levy and planted an elm in front of every
residence, and Winnipeg's splendid urban forest was born. It's
a democratic forest, lining not just the tonier streets of southern neighbourhoods
but also offering shade and comfort to people in Winnipeg's storied north end,
where successive waves of poor immigrants-most recently aboriginal people from
reserves-have settled in the rundown streets around Selkirk Avenue.
"Our forest is unique in the world," enthuses chief forester Mike Allen as he
surveys the elms that shade Palmerston Avenue in the Wolseley district. "There's
no other city anywhere with this incredible natural arch of trees." A tall, thoughtful
man with the image of a tree etched on his brass belt buckle, Allen grew up in
Toronto at a time when the dreaded Dutch elm disease was obliterating the elm
from the city's parks and lawns. "When I was eight," he says, "I noticed workers
removing one giant after another along my route to school, and whenever I
travelled around southern Ontario, I witnessed the death of elms standing like
weird witch's broomsticks." He has vowed not to let that happen in Winnipeg. He
points to a four-storey elm and describes the multipronged fight he has waged
against Dutch elm disease, explaining that the trees' rough and diverse origins on
the banks of the Assiniboine were the key to their survival.
"They're not high-tech clones cultivated for certain desirable traits," he says. "They
were selected purely from native stock, so they had tremendous genetic diversity
even though they were all one species. Today, I can show you elm from all over
Winnipeg, all American elm, but you might look at one and say, "That's not the
bark of an American elm.' "
As we tour the city's forest, it becomes clear that most Winnipeg elms have the
elm's characteristic bark, deeply furrowed and light grey, like a heavy grade of
rough corduroy. Some, however, have no fissures or ridges, and the bark is dark
or tinged with brown. Sometimes the leaves are enormous; sometimes they're
small. Some leaves have sawtooth edges and grow in double rows; sometimes the
edges are wavy and the rows are triple. Such variation makes for a more resilient
species, because certain variants seem to have an inherent resistance to Dutch
elm disease. Not all of them, however. Five years ago, in the biggest single elm
infection that Winnipeg has witnessed, the disease destroyed 20 mature elms at
Palmerston and Ethelbert. The memory still makes Mike Allen shudder. But the
resilient variants survived the infestation, and their genetic material may help save
the species.
Dutch elm disease, so named because it was first identified in the Netherlands in
1917 or 1918, likely originated in Asia. It's an infection of the deadly fungus
Ophiostoma ulmi, which enters and disrupts the tree's vascular system literally on
the back of the elm bark beetle, Hylurgopinus rufipes. The scourge reached the
United States in 1930, with the first Canadian outbreak reported in Sorel, Quebec,
in 1945. Within a few years, more than 600,000 elms in Quebec had been wiped
out. Toronto's population of 35,000 elms was quickly reduced by 80 percent.
According to the University of Toronto's Martin Hubbes, a leading Dutch elm
disease researcher, "one of the largest mass destructions of trees ever witnessed"
accelerated when the Canadian and American disease fronts merged and began
to migrate westward, travelling up the Red River from South Dakota into southern
Manitoba in the early 1960s, most likely brought in by campers hauling infected
firewood. The disease was reported in Winnipeg in 1975 and by 1990 was
infecting elms in Saskatchewan. This year, it arrived in Alberta. Today, possession
of elm firewood-infected or not-can bring a $5,000 fine in Winnipeg, where they
take the threat seriously. Since the disease's arrival, some 34 percent of city elms
have been infected and cut down.
It's a paradoxical story, at least as far as Winnipeg is concerned. The same
riverbank forests that provided the city with its rich genetic diversity now offer an
ideal host for Dutch elm disease. Because the Assiniboine, La Salle, and Seine
rivers empty into the Red near Winnipeg, their rich silt valleys provide both a
breeding ground and a highway for the elm beetle. The province has earmarked
and sporadically protected a buffer zone surrounding Winnipeg. This is a crucial
battlefield in the war to save the city's cherished elms. The idea is to remove
infected trees from this zone in an attempt to protect the city proper. Other western
cities that depend on the elm for shade, shelter, and beauty are luckier because
they are more like isolated islands in the prairie, with little contiguous elm forest.
Another paradox. Despite the devastation of the urban elm forests of Toronto and
Montreal, those central Canadian cities are well situated to bounce back. Their
relatively moderate climates can support a wide variety of trees, from the colourful
red maple to the elegant black walnut. Winnipeg's famously frigid winters mean
that few species can thrive there. The American elm, one of the hardiest, is ideal.
Not only sublimely beautiful, it's tough enough to resist road salt and devastating
cold. What's more, Winnipeg's harsh winters have little appeal for the European
elm bark beetle, Scolytus multistriatus, a larger, hairier critter that's a perfect host
for the toxic fungus. As long as Winnipeg has only the native prairie variety, its
elms have a fighting chance. Yet Mike Allen remains cautious.
"Insects are highly versatile and opportunistic," he warns. "It may well only be a
matter of time before we get European beetles reproducing themselves and
becoming hardy enough to invade Manitoba."
Part 1
Part 2
Part 3
Part 4
Copyright
How Trees Work
Part 1
Part 2
Part 3
Part 4
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
The past 20 years have witnessed widespread conflicts over
ancient trees and old-growth forests. A familiar snapshot:
Environmentalists cry foul, claiming the wilderness is being
strip-mined. Loggers and millworkers cry foul, claiming their
jobs are being jeopardized by a Birkenstock brigade of
outsiders who return to comfortable condos once the camera
crews depart. The conflict is, in a very real way, about a sense
of place. Many environmentalists plead for places they
cherish. That place, however, is often somewhere else: the
boreal forest, the Pacific rainforest, the wilderness. For many
Canadians, nature is, indeed, something out there in cottage
country, a wilderness park, a summer camp-a rural landscape, not a city
streetscape.
When Mary Anne Good planted the Wolseley elm, most Manitobans were sodbusting settlers. Twenty years later, when landscape architect Frederick Law
Olmsted urged Montrealers to make their new park on Mount Royal a naturalistic
retreat ("You can put in a broad dark mass of low mountain pine, or pensive,
feathery and brooding hemlock . . . to supply the degree of canopy and shadow
which will be the most effective for your purpose"), Quebecers were still by and
large country folk. We're about to enter the planet's first truly urban century: a
majority of the world's people now live in cities, and although Canadians may visit
a wilderness place from time to time, we pass our daily lives in the shadow of an
urban forest.
Urban forest may sound like a contradiction in terms, but not to Judy Werier, the
peppy director of Winnipeg's Coalition to Save the Elms. As we drive around
trendy Osborne Village to check out the condition of its trees, she hits the brakes
and jumps out of her car to rip a yard-sale sign off a sidewalk elm.
"Can you believe this?" she fumes, hurling the offending poster into the back seat.
"It was nailed to the tree! Someone actually used four nails!"
Jamming the car into gear, she mutters something about going over to the yard
sale on Saturday to scold the culprit. She explains that nails provide another way
into the tree for the elm bark beetle and wood-boring beetles and hence for the
fungus that causes Dutch elm disease. Heading along River Avenue, she has
trouble keeping her eyes on the road as she points out the cankerworm bands that
residents have dutifully wrapped around their neighbourhood trees, scolds
construction foremen for neglecting to strap protective lumber around trees on
building sites, and of course, keeps an eye out for the telltale flagging that
indicates an elm has been infected.
Citizen involvement has been crucial to Winnipeg's efforts to preserve the elm
forest. Coalition members report "hazard" elms to Mike Allen's department, where
every summer forestry staff adopt a war-room approach, sticking hundreds of red
and black pins onto a map as they chart sightings of the disease. There are lots of
pins along the rivers. The city uses an expensive fungicide injection system on
valuable park trees, while a less expensive basal spraying technique is aimed at
zapping beetles with an insecticide containing chlorpyrifos. This prevents the
beetles from overwintering in the tree but must be done annually. The principal
defence, however, is sanitation, which includes tree removal and pruning of dead
branches: some diseased trees can be saved by fungicidal injection, but many are
simply cut down. It's a $2 million-a-year battle, but Werier thinks it's worth it. Aside
from organizing workshops on tree planting, identification, pruning, and Dutch elm
disease, the coalition helped pressure the province into restoring some of the $3
million it had cut from the program to control the spread of the disease in the buffer
zone around the city.
"My husband calls me 'a crazy militant little person,' " she says as we head out
Portage Avenue. When I ask her about her commitment to the urban forest, why
she's such a tree zealot, she responds in the same way a wilderness tree hugger
might. "I love the trees," she says after a moment's thought. "That's all I can say.
There are no words I can put to it. It's emotional."
Werier got an early start in urban forestry. Her father, Val Werier, a longtime
Winnipeg newspaper columnist who recently won the Order of Canada for his
advocacy work, used to quiz her about trees, teaching her to tell an ash from an
elm. "When Dad came home from work, we'd go for a brisk walk. I'd have to run to
keep up with him, but he taught me about trees, and I developed a real
appreciation for them. So when I became involved with the elms, I said to myself,
'This feels right.' "
In 1969, Val Werier was pushing for a bylaw to control the removal of trees on
public land. Three years later, he was telling his readers to get out and put sticky
bands on elms to protect them from cankerworms. And in 1974, the year before
Dutch elm disease was first identified in Winnipeg, he wrote a long series of
columns on the imminent threat. By 1976, he was writing that government action
wasn't enough-Winnipeggers had to get involved in the fight against the disease.
Werier was soon able to point out that Manitoba was the first North American
jurisdiction to require the removal of diseased elms from private and public
property.
"There's a history of citizen activism here," Mayor Glen Murray told me when I
asked him about Werier. "And a very practical reason is that the absence of the
elms would have a huge negative impact on property values and the enjoyability
and livability of neighbourhoods."
A city forest has a long list of virtues. Urban air, full of carbon dioxide and a host of
noxious car fumes, is measurably improved in cities where a dense overstorey of
trees adds life-giving oxygen. The forest moderates storm runoff. A deciduous
forest protects houses from the summer heat, saving on air-conditioning costs
while permitting passive solar gain in wintertime. If it's dense enough-as it is in
Winnipeg-it acts as a winter windbreak. It also buffers the ceaseless white noise of
city traffic. Parents can take comfort that shaded play areas are safe in an era
when high-ultraviolet sunlight is cause for concern. Realtors know that a treelined
street is a price-boosting part of their "location, location" mantra.
Though she has a passionate attachment to the urban forest, Werier inherited a
lobbyist's understanding of how to protect it. She knows that she can't just rely on
the virtues of nature appreciation when it comes to navigating the political terrain
at city hall. A savvy politician, Glen Murray is well aware that Stephen Juba,
Winnipeg's longest-serving mayor, made an early and lasting impression when he
defended the Wolseley elm in 1957. "If you ever want to lose elected office in
Winnipeg," says the mayor wryly, "say something bad about a tree."
Of course, all the political will in the world will not stop the steady onslaught of
Ophiostoma ulmi. That's why Winnipeg, prodded by Werier and the Coalition to
Save the Elms, has been sending cheques to the Faculty of Forestry at the
University of Toronto, where Martin Hubbes and his research team have recently
developed a vaccine that immunizes the elm against the fungus. With patents on
the way, Canadian scientists have helped spark renewed international interest in a
problem that many had given up as a lost cause.
Part 1
Part 2
Part 3
Part 4
Copyright
How Trees Work
Part 1
Part 2
Part 3
Part 4
About Elm Trees
Caring for Your Elm
Elm Tree Diseases
Elm Tree Links
Quick Elm Facts
Hubbes began studying Dutch elm disease in 1968 and
quickly became fascinated by the many ways trees react to the
threat of infection. When bark beetles laden with fungal spores
burrow their way under the craggy bark of an elm, the tree
responds to the invasion with what Hubbes describes as a
"cascade of defensive reactions," including the production of compounds called
mansonones that help ward off fungal infestation. He and his colleagues have
succeeded in isolating from the fungus a glycoprotein "elicitor" that tricks the tree
into mounting its protective cascade.
"What the tree tries to do," explains Hubbes, "is to wall the fungus off in a confined
space so that it cannot further invade the vascular system. The trees actually shut
down the cell walls and surround the fungus with an inert tissue so that the fungus
cannot penetrate the tree further."
Once the defences are elicited and the fungus is isolated, the host tree is then
primed with antifungal mansonones (related to a group of substances called
sesquiterpine quinones) that destroy the fungus. "They kill by attacking
mitochondria, the energy powerhouses of the fungus," Hubbes told New Scientist
magazine last year after news of the discoveries began to filter out. Since then,
there's been a surge of international attention.
"It was incredible how a much renewed interest flared up around the world,"
Hubbes says now in his Toronto lab. A plant pathologist who seems torn between
modesty ("We didn't want a lot of propaganda because we like to work in a quiet
atmosphere") and bubbling enthusiasm for saving trees, he can't help letting the
enthusiasm surface. "We're getting inquiries from all over the world," he says, "the
U.S., Australia, New Zealand, Europe." Everyone, its seems, wants their elms
back.
Hubbes and his colleagues are busy conducting field tests in Winnipeg, Toronto,
and several other places in Ontario, treating trees with the elicitor and then
exposing them to high dosages of Ophiostoma ulmi spores "to see how good the
stuff is." They have also begun to treat elms in Saskatchewan and Alberta but
have carefully avoided introducing any fungus to vulnerable stands of elms there.
Results are already encouraging. In one trial, all the trees in the control group died
when exposed to the fungus, whereas only one in 33 vaccinated trees
succumbed.
Hubbes agrees that Winnipeg has a natural advantage because of its genetically
diverse elm population. But here again, Canada's richest urban elm forest presents
paradoxical problems inherent in any effort to intervene with a complex ecological
system.
"For our treatment, wide diversity within the species is not so good," Hubbes says.
"If I could just treat clones of a single variant, it would be so much easier for me
because one cloned tree would react the same as a thousand others. But where
there's high diversity, some trees do very well, while others require more
conditioning."
Another variable is the influence of the tree's environment. A handsome old elm
standing alone on a rural fence row may survive because it's being nourished by
good agricultural soils. "When you plant them in a city where you have a dreadful
environment," says Hubbes, "they might not react the same way. That's why we
have to understand the defence mechanisms. Once we do that, then I think we'll
have solved the problem."
Hubbes admits that even after 30 years of study, there's still much to learn about
the immune systems of Ulmus americana, particularly in a forest ecology as
complex as that of Winnipeg. But he is in no doubt about the prairie city's role in
sustaining the work that finally seems to be bearing fruit. "If Winnipeg hadn't
supported us," he says, "I would have given up a long time ago." Most people,
including Ottawa politicians and officials who have stopped supporting Dutch elm
disease research, still hear the word elm and immediately think of those skeletal
remains that dot the rural landscape in eastern Canada. Hubbes keeps getting
advice from people who say, "The elm? Don't bother. It's dead, forget about it."
But it's not dead in Winnipeg. "I grew up in Montreal when all of the elms died and
the city didn't act to save them," recalls Glen Murray. "I remember very vividly the
trees disappearing in my neighbourhood. Here in Winnipeg, people have a real
attachment to the trees. It's part of our identity as a city." And thanks to officials
like Mike Allen and citizen activists like Judy Werier, tree huggers whose
stubbornness was perhaps inherited from the women in the cloth coats who
defended the Wolseley elm, eastern cities may one day rejoice again under their
own restorative canopies of stately elms.
Part 1
Part 2
Part 3
Part 4
Copyright

Elmcare.com - All about elm trees and elm tree care.

Transcription

Similar documents

View presentation

Heritage Elm Tree Paintings

Loquat Respiratory Syrup with Slippery Elm and Cherry Bark

Lone Elm Logistics Center

Camperdown Elm - Moana Nursery

Directions

11 flyer draft

City of Mt. Pleasant FREE TREE PLANTING PROGRAM

eLM.MP3200iec.01.HardwareOverview 2