Lifestyles Of Famous Landscape Weeds: The Top 10

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Lifestyles of Famous Landscape Weeds: The Top 10
By: Hannah Mathers
For GLTE, January 2015
1.
Field horsetail (Equisetum arvense)
Fig. 1 A. Reproductive stalks of Horsetail taken April 2012, in sandy, low
fertility soil, shown withering and dying. B. Vegetative stakes forming
after reproductive stalks wither, bearing whorls of pine-needle-like
branches that look like a horse's tail.
On poorly drained soils, landscapers will have more problems
with field horsetail (Equisetum arvense), particularly if the plants chosen
for the site prefer well drained soils such as Ponderosa pine (Pinus
ponderosa) or Scotch pine (Pinus sylvestris). Horsetail thrives in moist,
low fertility and organic matter soils (Fig. 1A). Improving soil drainage is
one way to deal with horsetail problems. Increasing soil fertility and
organic matter are other ways. Field horsetail is a primitive plant type that
A
B
resembles a miniature evergreen (Fig. 1 B). Field horsetail is also known
as scouring rush, horse-pipes, bottlebrush and common horsetail. It
spreads by creeping rhizomes or underground stems and by spores. Short, thick, flesh- colored stems appear in spring. The strobilus, a cone-like
structure, emerges from the top of each thick stem (Fig. 1A). The strobilus bursts open when it matures, releasing spores which germinate in the
soil and form new plants. The difficulty with horsetail control is due to its well-developed root system, which grows and generates tubers up to 6
feet deep (Burill and Parker, 1994). Tubers are enlarged rhizomes with compressed internodes located at the ends of rhizomes. Cranston (1995)
indicates that horsetail roots can penetrate the soil up to 20 feet deep. Tubers production increases in full sun. Horsetail cannot tolerate shade.
Horsetail has two types of stalks, vegetative and reproductive. The vegetative stalks range in size from 6-18”, up to 3’. The
reproductive stalks are usually 3/4 to 1 1/2 “ in size but can be up to 1’ tall. Horsetail reproductive stalks wither soon after spores are released.
The later, green, vegetative shoot bears whorls of pine-needle-like branches that look like a horse's tail. Leaves are reduced to teeth-like scales
arranged in whorls around the joints of the stems. Vegetative stalks form in April and persist till fall frosts occur. Horsetail controls include
cultivation and mowing. Regular mowing will keep the plant growth down but will not kill it. Several sources indicate cultivation is not an
effective control measure; however, it is the depth of cultivation that is important. Shallow cultivation of less than 14” deep should be avoided.
Manual removal, digging and hand-removing rhizomes, is extremely difficult as stems easily break away from the rhizome. Do not remove soil
from contaminated areas as fractured rhizomes maybe transported.
Casoron 4G (Dichlobenil) applied at 100 - 150 lb product/ acre in early spring or late fall (do not apply when soil temperatures are
above 16ºC or 61ºF) will provided preemergence control of most spring-germinating annuals, post-emergence control of many winter annual
weeds and control of several perennial weeds including dandelion, field horsetail (equisetum), red sorrel, fescue, orchardgrass, & wild carrot.
Casoron is very water-soluble and can go off target easily and can move down slopes so be careful with applications around sensitive plant
material in these conditions. Limit Casoron use around azaleas to only on Kurume, Molis, hardy hybrid types, and hardy native species. In holly,
do not use on Ilex crenata, I. Rotunda, or I vomitoria. Pines are sensitive to injury from Casoron if applied within two years after transplanting.
Do not use on firs, hemlocks, or spruce. In research with Potentilla, viburnum, & lilac injury occurred when dichlobenil was applied before one
full season of growth. Altland (2004) indicates Casoron applied in three consecutive years of 4, 3 and 2 lb ai/acre suppressed horsetail.
Casoron can cause veinal, inter-veinal, marginal or overall leaf chlorosis or yellowing. At low concentrations, a halo effect or marginal
chlorosis is evident. Injury appears on the new growth. Plants may outgrow injury caused by low doses. At high rates, entire leaves become
chlorotic. Chlorotic areas may turn brown and die. Injury on broad leaf plants is sometimes more severe on leaves oriented toward the afternoon
sun. Herbicide carryover can be a problem when replanting a field with liners. Casoron is tied up by organic matter and slowly decomposed by
soil microbes. The chemical can remain active for 2-12 months. Rapid loss from the soil surface can occur if applied at temperatures higher than
those stated earlier, due to volatilization.
For postemergent control SedgeHammer (halosulfuron-methyl) is registered for use in turf and established woody ornamentals. It is a
broadleaf sulfonylurea herbicide that is probably the most effective postemergent in ornamental plantings. Manage is also good on other sedges
and horsetail. As discussed in nutsedge control, apply SedgeHammer to actively growing horsetail. Apply Manage at 1-1.3 oz/ac and include 1-2
qt nonionic surfactant /100 gal of spray solution or include crop oil concentrate at 1 gal/100 gal of spray mixture. Roundup does not work on
field horsetail. Consecutive applications of MCPA have proven effective (Altland, 2004). Approximately 20-30% of horsetail populations are
reduced with each MCPA application. However, skipping an application will allow plants to regenerate their depleted root system, and control
up to this point will have been lost (Altland, 2004). Spot application of the amine formulations of 2,4-D according to label instructions can
control this plant. 2,4-D amine is selective for broadleaf plants. To reduce vapor drift, use an amine formulation of 2,4-D rather than an ester
formulation. Precautions should be taken to avoid contacting non-target plants with the solution.
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2.
Quackgrass (Elytrigia repens)
Fig. 2. A. Clasping auricles are one of the distinguishing
characteristic of Quackgrass. B. The clump forming habit and
ability of even small pieces of rhizome to form new plants
increase the ability of Quackgrass to be one of the ten most
unwanted weeds.
Quackgrass has great reproductive ability through both
sexual and vegetative means. The rhizomes produced by a
single shoot may spread in diameter to about 3 meters or 10 feet,
with a large number of above ground shoots to form a dense
population (Werner and Rioux 1977). Control of Quackgrass
requires the suppression A
of both the top growth and the rhizomes
in the soil. Small pieces of shattered rhizome can regenerate a
new plant (Fig. 2 B); therefore, mechanical control alone is
insufficient for control (Altland, 2004). Some synonyms of
Quackgrass are Agropyron repens, quitch grass, couch grass, devils-grass or quick grass. Stems grow up to 3 feet
tall with 3-6 joints. The clasping auricles’ of the leaf blades around the stem is used to positively identify this species (Fig. 2 A). Plants form in
clumps (Fig. 2 B) and flower in June and July. The seed head is a long spike (5-20 cm). Spikelets are 4-6 seeded and 1-1.5 cm long, arranged in
2 rows along the axis (Uva, et al., 1997). Seeds mature early August to September. There are commonly 25-40 seeds per stem. Seeds drop in
late September where they overwinter in the leaf litter or on the ground. Seeds can remain viable for 1- 6 years (Reidy, 2001). Viability is
maintained even after passing through the digestive tract of most farm animals, except swine. This is important to keep this viability in mind if
you are placing animal manure on an ornamental site.
Quack grass is a temperate or cool season grass. In the spring and fall, it grows vigorously by producing approximately 2.5 cm (1 inch)
of new rhizome growth per day (Reidy, 2001). It prefers fine-textured, neutral to alkaline (pH 6.5 to 8.0) soils with moderate soil moisture.
Quackgrass is drought tolerant, however, and can withstand high quantities of salt (Reidy, 2001). In corn, soybeans and wheat Quackgrass can
reduce yields by 25-85%, 19-55%, and 57%, respectively. It is estimated Quackgrass can absorb approximately 55, 45 and 68% of the total
nitrogen, phosphorous and potassium, respectively, available for plant use (Reidy, 2001). On the positive side, research indicates that
Quackgrass is one of the most effective plants for reclaiming nutrients, such as nitrogen, from sewage effluent sprayed on vegetation.
Glyphosate is a non-selective herbicide capable of Quackgrass control (Ivany, 1988). Glyphosate is the active ingredient in Roundup
Original, Roundup Pro, Roundup Ultra and many other generic brands. Ivany (1988) found that top growth control of Quackgrass at 0.56 kg/ ha
(0.5 lbs/ac) of glyphosate with the addition of ammonium sulphate was comparable with that of the label rate of 0.9 kg/ ha (0.8 lbs/ac). Periodic
applications at the high rate of 0.9 kg/ha (0.8 lbs/ac), in combination with the 0.56 kg/ha (0.5 lbs/ac) rate and ammonium sulphate, gave effective
rhizome control (Hamill and Zhang, 1995). There is no real consensus on the effectiveness of ammonium sulphate to improve the efficacy of
glyphosate. However, one proven method for increasing glyphosate efficacy, in seasonal Quackgrass control or in situations where cultivation
has occurred, is to use lower water volumes. By lowering the water volume to five gallons per acre, Glyphosate can be applied at 2.4 L/ha (0.26
gal/ac) versus the label rate of 7L/ha (0.7 gal/ac). The best way to apply glyphosate for Quackgrass control is to apply it in the fall and follow
with tillage (R. Zondag, personal communication). Apply the glyphosate in the fall and allow it to act on the plant at least 1-2 weeks. Fall
applications are most efficacious for perennial weeds such as Quackgrass because the herbicide is taken down into the root system more readily
in a fall application versus spring. Fall tillage is more effective in reducing the total amount of rhizomes present in the soil than spring tillage
(Reidy, 2001). Fall tillage exposes the rhizomes to desiccation from cold temperatures and winter winds. Tillage with a moldboard plough also
distributes the rhizomes more evenly in the plough layer. The deeper the rhizomes are in the soil profile the uneven the emergence pattern of the
shoots, allowing herbicides to work more effectively (Reidy, 2001). The best grass-active herbicide is Fusilade. Fusilade II will provide superior
control for Quackgrass in nursery and landscape settings versus Vantage or Envoy. Good preemergent control can be achieved with Princep or
Casoron 4G; however, check the label carefully for stock tolerance and restrictions, ex. do not apply Casoron when soil temps are above 16°C
(61°F) on sandy soils or soils with less than 2-3% organic matter.
3.
Field Bindweed (Convolvulus arvensis)
B
A
Fig. 3B. The leaves of field bindweed are smooth, slender, and
slightly angled about one to two inches long, arrow shaped,
with a blunt base. The stems can long, vine like and trail on the
ground forming a dense mat (A) or wind around and strangle
other plants and objects. A. The flowers are like morning
glories.
Field bindweed has been given many names including
perennial morning glory, creeping jenny bellbine, sheep-bine and corn-bind. Mature field
bindweed plants have arrowhead-shaped leaves (Fig, 3 A) that can be between ½ to 2 inches long. The flowers are trumpet shaped, white to pink
in color and 1 to 1 ½ inches wide (Fig. 3B). Field bindweed is a prostrate plant unless it climbs on objects for support. Field bindweed is
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considered a noxious perennial weed that is difficult to kill because of its extensive root system. The root system has vertical roots that can reach
depths of 20 feet or more and shallow horizontal roots, mostly in the top 2 feet of soil, that make up 70% of the total root mass. Experiments
have shown that its root and rhizome growth can reach 2 ½ to 5 tons per acre (Elmore and Cudney, 2004) and rhizome fragments as short as 2
inches can form new plants. Lateral roots at approximately 15 to 30 inches from the parent plant turn downward, becoming a secondary vertical
root. It then sends roots and shoots from the turning point; therefore, a single bindweed plant can spread greater than 10 feet in diameter in a
growing season. An average plant produces about 500 seeds that may be viable up to 60 years (Elmore and Cudney, 2004). Drought tolerance is
a characteristic of field bindweed and can out compete other plants when water is withheld (Elmore and Cudney, 2004).
Cultivation or hoeing has been partially effective in reducing established stands of field bindweed. Cultivation about every 2 to 3 weeks
as soon as the bindweed reaches 6 inches in length and repeating as necessary is required. Hand-pulling well-established bindweed will not kill it
because of its root system. Herbicides such as Roundup (and other formulations of glyphosate) and 2,4-D Amine or related chemicals (such as
Dicamba) can be effective in managing bindweed, but killing it with herbicides will take several applications over a period of years. Tordon 22K
can be used in non-crop areas and is a restricted use product. Combinations of Roundup and dicamba in non-crop areas will give some residual
activity to control new seedlings. Late summer or early fall applications are most effective for postemergence. All postemergence must be used
with extreme caution keeping contact or drift away from desired ornamental plants. Herbicides should always be used in conjunction with
appropriate preventive and cultural controls. For lasting control, a three-phase treatment plan should begin at first blooming and continue
through fall: 1) treat with an approved postemergence and other methods shortly after flowers appear; 2) re-treat new bindweed growth
approximately 30-45 days after initial treatment or when 12”-18” runners exist; 3) re-treat returned growth with a systemic herbicide after first
frost in the fall, but before night temperatures reach 20°F. Preemergence such as trifluralin, oryzalin or pendimethalin containing products will
reduce emerging perennial shoots and control germinating seedlings; however, they will not kill established bindweed plants.
4.
Canada Thistle (Cirsium arvense)
A
Fig, 4. A. Canada thistle (CT) leaves are alternate, sessile, simple, oblong to lanceolate. Leaves are
irregularly lobed, developing into triangular indentations with age, with spiny margins. Upper
surface of mature leaves is dark green
and hairless, while the lower surface is
light green in color and may be with or
without hairs. It is a perennial that
reproduces from seed and by an
extensive root system. Roots may
extend 15 feet horizontally and
vertically 6 to 15 feet. Nearly all parts
of the roots can produce buds, which
B
gradually develop into shoots that grow
and form new plants. Root segments as small as 1 inch can form a new plant. B. A solid mat of CT
forming in a Buxus field.
Tillage and movement of root pieces can spread plants. Canada thistle is dioecious with male and female flowers on separate plants.
The flowers are purple and appear from June to September. The number of seed produced per head will vary from 1 to 100 and seeds can be
viable up to 20 years. Repeated and frequent hand pulling or hand-cutting of individual plants will eventually starve underground stems.
Cutting or pulling should be done at least 3 times each season, in June, August and September. These treatments are feasible for light and
moderate infestations, but may be relatively time consuming for heavy infestations. Spot application of the amine formulations of 2,4-D
according to label instructions can control this plant. 2,4-D amine is selective for broadleaf plants. To reduce vapor drift, use an amine
formulation of 2,4-D rather than an ester formulation. Precautions should be taken to avoid contacting non-target plants with the solution. 2,4-D
combined with dicamba as a split-season application is effective. Apply 2,4-D, 2 quarts per acre, in spring when Canada thistle is 10-15 inches
tall, in pre-bud to early bud stages, retreat in fall with dicamba (2 quarts/A) to re-growth. A foliar application of a 1-2% solution of Roundup
applied in spring when plants are 6-10 inches tall is an effective treatment. Roundup is a non-selective herbicide and precautions must be taken
to avoid contacting non-target plants. Combinations of Roundup and dicamba in non-crop areas will give some residual activity to control new
seedlings. As with bindweed, Tordon 22K can be used in non-crop areas only. Tordon applied in the fall is especially effective; however, it can
be used any time the plant is actively growing.
Herbicides containing the active ingredients clopyralid (Stinger or Lontrel) are reported to be the most effective, and should be applied
as soon as plants have emerged from the soil. Arnold Appleby, a retired Oregon State University weed scientist, reports that the most effective
control is achieved by applications of Lontrel in late September with 2/3 pint/acre followed by application in spring with 1/3 pint/acre (Appleby,
1999). Clopyralid can cause severe injury to some crops. Always use directed applications to avoid injury on ornamental plants. When making
applications in landscape sites, Lontrel is the labeled product (Stinger is labeled for ag crops). Due to issues surrounding residual clopyralid in
compost, the ODA developed new restrictions for using the herbicide in turf areas. Lontrel is also very effective on Broadleaf plantain, Clover,
Dandelion, Groundsel, Horseweed, Ragweed and Vetch. Preemergents such as Casoron, SureGuard and Plateau will reduce emerging perennial
shoots and control germinating seedlings; however, they will not kill established plants. The key principle to Canada thistle control is to stress
the plant and force it to use stored nutrients. Success requires a sound management plan implemented over several years.
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5.
Yellow Nutsedge (Cyperus esculentus L.)
Fig. 5. Yellow Nutsedge is a fibrous-rooted perennial, has erect triangular yellow-green stems
that grow 12 to 32 inches tall. Each new plant will be topped by a cluster of yellowish-brown
(straw-colored) seed heads (inflorescence) that can produce hundreds of millions of seed per acre.
Yellow nutsedge is extremely competitive and reduces landscape plant growth by
competing for water, light and nutrients. Viability of a mature seed is relatively low, ranging from
5 to 40 percent; therefore its main means of propagation is its extensive underground system of
rhizomes and tubers (or nutlets) that store large reserves of energy. This system allows the plant
to overwinter and produce new shoots the following spring. Brownish to rust-colored the oval
nutlets measure¼ to ½ inch in diameter and form on the ends of the rhizomes in the upper 6 inches
of the soil. Yellow nutsedge primarily reproduces from its tubers. One plant can produce several
hundred to several thousand tubers in a single growing season. The tubers break dormancy in
winter and germinate in the spring. Each tuber has several “eyes” that can produce two or three
sprouts or plants. Dormant tubers require long-term effort to control.
Prevention, of course, is a primary means of control. Watch tillage operations as not to
spread tubers to other areas. Maneuvering tillage equipment around isolated nutsedge patches to avoid spreading rhizomes and tubers is
recommended. Fall tillage, is recommended, as it will expose tubers to cold temperatures, which can reduce tuber and rhizome populations.
Spring tillage is less effective. Hot, dry, and breezy weather conditions will enhance the effects of cultivation by quickly drying out the uprooted
plants and nutlets. Avoid spreading manure contaminated with nutsedge into fields or landscape beds. Watch soil being brought on the site and
compost for potential contamination by seeds and tubers. Spot treat isolated patches of nutsedge with postemergents; see spot treatments below
for directions.
Herbicides, when used in combination with mechanical, cultural, and preventive methods, are an integral part of a yellow nutsedge
control program. However, some annual weed control programs may actually increase the nutsedge problem by removing annual broadleaf and
grassy weeds, allowing yellow nutsedge to thrive and become difficult to control (Lingenfelter and Curran, 1995). For effective soil-applied
treatments, a uniform concentration of herbicide must be placed within the upper 2 inches of the soil surface (Lingenfelter and Curran, 1995). It
is important to select controls that account for the perennial growth of yellow nutsedge. In a trial conducted by Ohio State University we found
SedgeHammer and FreeHand herbicides were the most effective treatments. Although SedgeHammer is a postemergence herbicide in our trial
we applied SegeHammer and FreeHand preemergence in April and had control through to July with both products. SedgeHammer - in turf and
established woody ornamentals should be applied postemergence to plants 4-12” at 1-1.3 oz/ac + 1-2 qt nonionic surfactant /100 gal or crop oil
concentrate at 1 gal/100 gal. Basagran T/O (sodium bentazon) is another effective postemergence nutsedge herbicide. It is best used as a split
application when the nutsedge is 6-8” at 1.5 -2 pints/ac + 1 qt/ac of crop oil concentrate and then the same rate 7-10 days later. Atrazine >4” +
Basagran can be used to provide residual control. Mature tubers are unaffected by Round-up.
6. Marestail (Conyza sp.)
Fig. 6. Marestail can follow a winter annual or a summer annual life cycle; therefore, it can emerge in the fall
and in the spring.
Fall emerging Marestail will have a more extensive root system than those that emerge in the spring
(Johnson and Nice, 2003). The more established root system of the fall emerging plants make them more difficult to
control because they can resprout from meristems in the lower part of the stem and roots. Therefore, systemic
herbicides are required in “high enough quantities” to inhibit this resprouting (Johnson and Nice, 2003). Larger older plants have more active
meristems so herbicide translocation and early control are key factors. In fact, glyphosate products (Round up, Touchdown, Roundup Ultra, etc.)
provide fairly good control of seedlings 4 inches or less in height. Many control failures with glyphosate products have occurred when Marestail
greater than 1 foot are sprayed. Weather conditions will of course also influence the action of the systemic herbicides. Weeds growing in very
wet or very dry soils generally, have slower rates of metabolism; therefore, weeds growing in these conditions result in compromised herbicide
activity (Johnson and Nice, 2003). The addition of 2,4-D to glyphosate will improve control of larger Marestail plants. However, use of
glyphosate, 2,4-D and especially glyphosate + 2,4-D combinations must be used with extreme caution around ornamental plants, as glyphosate is
a non-selective herbicide and 2,4-D a broadleaf killer. In landscapes no contact of these products must occur to the ornamental material,
including green bark.
Marestail control has recently become more difficult due to the advent of glyphosate and ALS resistance biotypes. ALS inhibitors are
common for use in field agriculture; however, in ornamentals we only have three herbicides that functions by this mode of action, Plateau, Image
and Manage. Jeff M. Stachler, Mark M. Loux, Jeff Taylor, Geoff Trainer, and Traci Bultemeier, researchers at Ohio State University in the
Department of Horticulture and Crop Science, through fall of 2003 have confirmed ALS resistance in 20 Ohio counties mainly in the Southwest
part of the state and 17 counties in the SW with glyphosate resistance. ALS-Resistant Species have included Powell amaranth, common
cocklebur, kochia, common lambsquarters, marestail, smooth pigweed, common ragweed, giant ragweed, shattercane and waterhemp (Stachler et
al. 2004). They have also confirmed 2, 4-D resistance and atrazine resistance in 2 Ohio counties.
If the fall is relatively dry fewer seedlings will emerge as winter annuals. If the winter is harsh than fewer weeds will also emerge as
winter annuals. This will also be true of henbit, chickweed and marestail. If the spring is dry fewer Marestail seedlings will emerge as summer
annuals (Johnson and Nice, 2003). 2, 4-D products provide good control of marestail and is a cheap product to use. However, again, it must be
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used with extreme caution around ornamental plantings. It can be used as a burn down in non-crop areas, fallow fields, and with caution to get
no drift around ornamentals. Using 2,4-D is a good strategy, if used correctly, because it offers another mode of action on Marestail that will
slow the development of more resistant weed populations. Lontrel is also registered for postemergence control. Valent's new product SureGuard
(flumioxazin) is also effective on Marestail as a preemergence. The SureGuard also offers an alternative mode of action and is best used for this
weed as your fall preemergence in landscapse. Other preemergent registered for Marestail include, Simazine, Dimension, Diuron, Gallery, Goal,
Oryzalin, and Snapshot.
7.
Creeping Charlie (Glechoma hederacea)
Fig. 7. Creeping Charlie is also called ground ivy, gill-over-the ground and creeping Jenny.
It is classified by life cycle as a creeping perennial. It can also be confused with Henbit,
which is a winter annual. Henbit is non-aggressive; however, ground ivy is considered
invasive and hard to control. Henbit and ground ivy are difficult to separate because both
produce round, toothed leaves, square stems and opposite leaf arrangement (in the mint
family). Their flower shape (tubular) and flower color (lavender-blue) are also identical.
Both grow well in shady, poorly drained, fertile soils, where creeping Charlie especially will
thrive and become a major problem. However, ground ivy leaves have petioles; Henbit
leaves are attached to the stem and mature henbit has a more erect habit than ground ivy.
Henbit also has a single taproot; Ground ivy roots out at each node that touches the ground.
Henbit has hairy leaves; ground ivy leaves have far less pubescence.
Ground ivy can also be confused with Violets (Viola sp.). Violets include winter
annuals and perennials that are low growing. Violets prefer the same sites as ground ivy. Leaves of common violet are oval to kidney-shaped
with a heart- shaped base. Flowers may be white, blue, purple or yellow of violets. They reproduce by seed and spread by creeping roots and
rhizomes. Hand weeding and hoeing of ground ivy and violets can be tedious due to the rooting at every node and leaving of pieces behind.
The most effective postemergent controls contain a combination of two to three broadleaf herbicides. The most effective combinations
contain dicamba, dichlorprop and/or triclopyr (Prostak, 2001). However, applications will need to be repeated at 10-14 day intervals at least two
times. Very late fall applications are most effective for perennial weeds with systemic herbicides. The next best time is when the plant is in its
early flowering stage. Again, as mentioned earlier for broadleaf herbicides, avoid contact with ornamental plants, application with dicamba in
the drip line of the tree. Always spray on clam days when air movement is away from the sensitive plant material and temperature will be below
85°F to reduce volatilization of the herbicide. Temperature in the 60’s and 70’s are best. Liquid applications are more effective than granulars.
Ground ivy and violets usually encroach into landscape beds from turf. So control in turf is the first line of prevention. Maintaining a
thick lawn goes a long way regarding control of these two weeds. To reduce shade in problem areas – prune trees and shrubs in those areas to
allow more light penetration to the turf. Roundup can be used in turf areas where renovation and starting over are required.
8.
Prostrate/ spotted spurge (Chamaescyce maculata or C. humistrata)
Fig. 8. Prostrate/ spotted spurge (Chamaescyce maculata or C. humistrata)
is known as a warm-season weed and the openness of the crop’s canopy
directly influences its germination (Mickler and Ruter, 2001).
Prostrate spurge in nursery containers has been identified as one of
four, of the most difficult weeds to control (Gilliam et al., 1990) and one of
six, of the most dominant weed species (Penny and Neal, 2000). Mathers
(1999) found that spurge was also one of the most competitive weeds.
Growing in Oregon nursery containers, spurge resulted in significant growth
and quality reductions in Azalea 'Rosebud' and 'Gold Cone' Common
Juniper. Prostrate/spotted spurge also dominates containers in mid to late
summer (Penny and Neal, 2000). Optimum conditions for spurge
germination include temperatures of 25-30 ºC and light (Krueger and Shaner,
1982). Prostrate spurge germination is also influenced by fertilizer
placement, methods that limit nutrient availability in the top surface of the container reduce spurge establishment (Fain and Knight, 2003). After
incorporating controlled release fertilizers (CRF’s), Ruter and Glaze (1992) reported 96 and 86% control C. humistrata 8 and 12 weeks after
treatment (WAT), with combinations of the herbicides, Ronstar (oxadiazon) + Surflan AS T/O (oryzalin). However, Whitwell and Kalmowitz
(1989) after topdressing CRF’s found that C. humistrata control with combination herbicides was 59 and 52% control 8 and 12 WAT,
respectively. Altland and Fain (2003) speculate that fertilizer placement may explain some of the discrepancy between results in these two
studies. In addition to the two studies listed above other researchers have found only combination herbicides provide spurge control after 30-45
DAT (Fare and Robinson, 2001; Judge and Neal, 2000). Of five herbicides that provided effective control at 28 DAT only Gallery (isoxaben) +
Surflan was providing spurge control at 70 DAT (Judge and Neal, 2000). Fare and Robinson (2001) found OH2 (oxyfluorfen + pendimethalin),
provided that best spurge control at 90 DAT. Judge and Neal (2000) also found that reducing Gallery from 1 lb ai/A (1X) to 0.5 lb ai /A (1/2 X),
resulted in a drop from 100% to 54% in spurge control, respectively. They also found Gallery had greater activity in a sand-only media
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compared to a bark+sand (7:1 v/v) media. Fare and Robinson (2001) also found that containers receiving cyclic irrigation at 45 and 90 DAT
versus once daily had significantly less control.
9.
Wild Garlic (Allium vineale)
This weed is an increasing problem in Ohio nurseries. It is a bulbous perennial. Fibrous roots are attached
to the bottom of a rounded to egg-shaped bulb (Fig. 5). The bulbs have a papery outer coating (Uva et al.
1997). Bulblets form at the base of larger bulbs (Fig. 5). Reproduction is by aerial bulblets and the
underground bulblets and rarely by seed (Uva et al. 1997). Bulblets often remain dormant over the winter
and germinate the following spring or 1-5 years later (shown above). Growers in Ohio report that wild
garlic “quickly becomes a problem” in a nursery field. “Where one plant was last year, five plants come up
the following spring.” Flowers (shown above) or aerial bulblets are produced in May and June at the top of stems (Fig. 6) these later become
globe-shaped umbels (Uva et al. 1997). Wild garlic is also known as field garlic or wild onion. Wild onion (Allium canadense), however, as the
scientific name indicates is a different species. The leaves of wild onion are flat in cross section, not hollow, and the bulb has a fibrous, netveined outer coating, not papery and thin like wild garlic. Wild garlic usually grows on rich soils but can tolerate a wide range of soil conditions
(Uva et al. 1997).
Suggested controls include 2,4-D products when the plants are quite small and 2,4-D + Gallery. Again, 2,
4-D products are broadleaf postemergent weed killers and generally only used in non-crop nursery areas, never as
over-the-top applications. Late fall tilling has been effective in row crops as the bulblets are exposed to killing
temperatures (C. Elmore, personal communication). Plateau and Image 70 DG are registered pre/post emergent
controls.
10. Winter Annuals
Common Chickweed (Stellaria media) - Chickweeds and Stitchworts (Stellaria sp. and
Cerastium sp.), and Pearlwort (Sagina procumbens) Are all members of the pink family.
Most preemergents work on members of the Pink family, including Simazine, Diuron,
Casoron, Surflan, and Kerb. Many Pink family members, however, are resistant to Ronstar.
Glyphosate and Paraquat give good postemergent controls; however, 2,4-D provides good to
A
poor control depending on the specific species. Chickweed is often found growing out of the
drain holes of containers growing on geotextile mats that cover the container yard or the floor
of a polyhouse. High nutrient content, standing water and small amounts of media that flow
with the excess irrigation out of the containers’ drainholes create an ideal environment for chickweed.
Bii
.
A. Hairy bittercress (Cardamine hirsuta) is one of the most common weeds
found in nursery containers; however, with an effective weed management program, it
can be controlled. Isoxaben (Gallery) and imazaquin (Image) are recommended for
postemergence control of Cardamine hirsuta, although Gallery was not as phytotoxic as
Image on the plants evaluated. Research demonstrated that Gallery provided excellent
post emergence control of hairy bittercress with no injury to a broad spectrum of woody
ornamentals, and that control was influenced by size/age of the weed. Small nonflowering bittercress (Fig. Bi)
were controlled with 1.0 pound
active ingredient per acre, while
2.0 pounds were necessary to
control large, flowering
bittercress (Fig. Bii).