WGF160_How to deal with pansy diseases.indd

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How to deal with pansy diseases
Pansies and their relations are subject to several specific diseases
including pansy downy mildew, pansy leaf spots and pansy sickness
Q
A
What is pansy downy
mildew?
This disease is caused by the funguslike organism Peranospora violae.
It has only become a problem relatively
recently, possibly encouraged by several
mild winters that have allowed spore
numbers to build up.
Q
What plants does it affect?
A
The disease is most often seen in
bedding pansies and violas, but may
attack related species including violets
and wild pansies.
Q
How do I recognise it?
A
Growth of affected plants slows down
and they look generally unhealthy.
The surface of infected leaves turns pale
green or yellowish, and they may roll
down at the edges. Grey, downy patches
appear underneath.
Q
A
Could I mistake it for
anything else?
Pansies can also be affected by
powdery mildew, but, with this
disease, which is unrelated to downy
WGF160_How to deal with pansy diseases.indd 1
mildew, the grey patches are on the
upper leaf surface and tend to appear
in dry rather than wet weather.
Q
What damage does it do?
A
Badly affected leaves may die, so the
disease is disfiguring and reduces
flower production, though mature plants
will usually survive.
Q
What is its life cycle?
A
Downy mildews can only grow and
reproduce on living plant material
where they produce spores, which can be
carried in the air over very long distances.
Otherwise they survive in the soil as
resistant spores, which can be spread
in plant debris, on shoes, tools and
equipment, or with bought-in plants.
Q
When do attacks occur?
A
Attacks can occur at any time, but
the disease spreads most rapidly
in damp weather when plants are
continually moist.
Q
How do I control an attack?
A
There are no chemicals available
to gardeners to treat this disease.
Picking off affected leaves as soon as the
problem is spotted may help to reduce
the severity of an attack.
Q
How do I prevent it in future?
A
Always buy healthy, well-grown plants
and do not overcrowd them. Do not
soak the leaves when watering, water
directly onto the soil. This is particularly
important in containers, where plants
will be more crowded than usual. Avoid
replanting pansies in the same soil or
potting compost to reduce the risk of
spore numbers building up.
Q
What are pansy leaf spots?
A
A variety of fungi cause spots on
pansies and violas, particularly
winter-flowering varieties. Large,
disfiguring black spots are likely to be
caused by Mycocentrospora acerina;
brown, scorchedspots by Ramularia
agrestis; and dark, greasy-looking spots
with brown centres by Ramularia lactea.
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Q
What plants do they affect?
A
These fungi can affect pansies, violas
and violets, including wild species.
Mycocentrospora also affects other
genera, causing leaf spotting on a wide
range of flowering plants, and root rot
in carrots, parsnips and celery.
Q
How do I recognise them?
A
Leaf spots appear as distinct, separate
spots, whereas mildews create more
irregular patches of discolouration.
Q
What damage do they do?
A
Mycocentrospora can kill plants
by rotting the crown. The other
infections are generally confined to
the leaves, so are largely cosmetic.
Q
What is their life cycle?
A
While growing on the pansies, the
fungi produce spores, which are
generally spread by rain or in surface
water. They can also produce resting
spores that can survive for many years
in dead plant remains in the soil, ready
to infect new plants.
Q
When do attacks occur?
A
Leaf spots are most likely to develop
in mild, moist conditions. The spores
do not travel far, so infection will generally
come from wild pansies or violets nearby,
or from soil or compost where pansies
have been grown before.
Q
How do I control an attack?
A
Several general, systemic fungicides
are approved for use on pansies and
should help to control leaf spot diseases
if applied when symptoms are first seen.
These are myclobutanil, sold as Fungus
Clear Ultra Gun (spray) Fungus Fighter
Disease Control (spray) and Systhane
Fungus Fighter (concentrate), and
triticonazole, found in Scotts Fungus Clear
Ultra (concentrate).
Q
A
What are the organic
options?
Removing badly affected leaves will
check the spread of the problem.
Q
How do I prevent it in future?
A
Inspect plants carefully before
buying to check there are no signs
of leaf spot, or grow your own from
seed. Avoid growing pansies or violas
in soil or compost that has been used
for them previously.
Q
What is pansy sickness?
A
This is a soil-borne disease, also
known as stem rot. It is caused
by the fungus-like organism Pythium
violae, related to the species that causes
damping off in seedlings.
Q
What plants does it affect?
A
This species of pythium can affect
any plants in the viola genus, though
it is normally seen in bedding pansies
or violas. It also occurs as a secondary
infection in carrot cavity spot, where
it causes root rotting.
Q
How do I recognise it?
A
Plants wilt and collapse, as if they are
short of water, even though the soil is
moist. Foliage turns yellow, flowers shrivel,
roots fail to grow and the plants ultimately
die. Stems break easily near ground level.
What is its life cycle?
A
Pythium is not a true fungus, but
behaves in a similar way, producing
resistant spores that remain in the soil
to infect new plants.
Q
When do attacks occur?
A
Pythium spores inhabit the soil,
waiting for the appropriate plant
species to infect. If the same plants are
grown in the same area year after year,
levels of infection build up to the point
where plants are seriously damaged.
Q
How do I control an attack?
A
There is no chemical control for
pansy sickness. Once attacked, plants
are unlikely to survive and should be
removed and disposed of. If only some
plants succumb initially, move the others
to a different part of the garden, where
pansies or violas have not been grown
recently, or put them into containers of
fresh compost.
Q
How do I prevent it in future?
A
Avoid growing pansies or violas in the
same ground year after year. If this is
unavoidable, remove the soil to a depth of
30cm every few years and replace it with
soil from another part of the garden.
Q
A
Could I mistake it for
anything else?
Wilting from lack of water may look
similar, but should not produce
yellowing and is generally reversible
once the soil is watered.
Q
How serious is it?
A
Many plants will fail to establish and
die if grown in soil with high levels
of Pythium violae infection.
For the full selection of Which? Gardening factsheets, see www.which.co.uk/wgfactsheets
WGF160_How to deal with pansy diseases.indd 2
Q
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experts during one of
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See Which? Gardening
magazine for details
December 2014
17/12/2014 15:47