Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Anthracnose Leaf Blight of
Shade Trees
A number of different trees are affected by anthracnose diseases.
These fungal diseases can cause severe leaf blighting and deformation, but in
many cases damage to plant health is not severe. However, with sycamore
anthracnose and dogwood anthracnose, the fungus regularly moves back into stem
tissue and causes more significant problems. Following are profiles of some of
the more common anthracnose diseases of landscape trees.
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Maple Anthracnose Anthracnose
diseases are generally not severe on maple, but can cause considerable unsightliness
from brownish leaf blotches and some leaf drop when moist weather conditions
make the disease particularly severe. Extensive development of stem
infections is not common on maples, as it is with sycamore anthracnose, and
dogwood anthracnose. The
most common symptoms include brownish –discoloration along veins, varying
from discrete spots to irregular patches of discoloration bordered by veins.
Spore masses of the fungus can sometimes be found on lower leaf surfaces
along veins during extended moist conditions. The fungus spreads from
previously infected tissue in spring to new growth. Where fungicides are used, applications
must be started at bud break and continued during early leaf development. |
Anthracnose on maple leaf |
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Ash Anthracnose This
anthracnose disease is primarily a leaf blighting and blotching disease of
white ash and to a lesser extent, green ash. Small twig cankers do occur and
the fungus over winters on these twig lesions, but little damage occurs from
this phase of the disease. In wet, cool spring conditions, leaves and
sometimes shoots first develop water soaked areas and later large tannish blotches and leaflet distortion. Considerable
leaf drop occurs, especially from lower areas of the canopy. Though this causes concern when leaves
litter the ground in late spring, damage to overall plant health is not
generally severe and plants typically re-leaf. As leaves mature they tend to
become more resistant to infection. Fungicide applications, if warranted, should
be made at bud break, with several repeat applications early in the season. |
Anthracnose on ash leaf |
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Oak Anthracnose White
oaks are the most susceptible of many oak species to this leaf blotching disease.
Twig infections occur but are not significant except as sources of over
wintering fungal inoculums from year to year. Leaves and shoots are infected
during cool, wet spring conditions causing leaf blotches that often are
strictly delimited by leaf veins. Eventually, lesions become a papery tan
color and some leaf shriveling occurs. Multiple cycles of infection can
occur. Just as leaves near maturity,
lesion size lessens, and once leaves mature they become fully resistant by
early to mid summer. Fungicides are generally not recommended. If fungicide
is required, use a labeled material containing thiophanate-methyl,
chlorothalonil or mancozeb. |
Anthracnose on oak leaves |
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Sycamore Anthracnose This is
a potentially serious disease of American sycamore and to a lesser extent
London planetree. Susceptibility of London planetree varies considerably with seed source. Shoot
blight, leaf blight and twig and branch cankers and dieback can be severe.
The fungus over winters on twig tissue on the tree with spores splashing to
new buds, shoots and leaves in the spring, with disease being enhanced by
cool, wet conditions during shoot and leaf development. Considerable
defoliation, sometimes with complete leaf loss, occurs on many trees by late
spring in some years. Trees
typically re-leaf by early to mid summer and are less susceptible to
continued infections because of warmer, drier, conditions. Also, as leaves
age they become less susceptible to infection .With repeated infections over
the years, cankering of twigs and branches can result in erratic shoot growth
that gives an overall distorted, appearance to the tree and also witches brooming where there are numerous side shoots that
develop around a central terminal shoot that was killed by the fungus.
Fungicide applications to prevent infections in the spring are sometimes
warranted. |
Anthracnose on a sycamore leaf |
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Dogwood Anthracnose In recent
years this disease has become prominent in certain areas especially on
flowering dogwood (Cornus florida). Dogwood anthracnose is most severe where
cool, moist conditions occur during the summer, such as in higher elevation
areas, and in densely vegetated shady sites with
poor air movement. Leaf symptoms
include irregular brown blotches bordered in purple on upper leaf surfaces
(tan in color viewed from the leaf underside). Leaf lesions often are
delimited by the leaf mid-vein. Stem
symptoms include twig dieback and stem cankering and dieback, often with
visible fungal fruiting bodies on dead twigs.
Attached wilted, brown leaves often persist into the next spring
instead of dropping in the fall.
Plants may be killed. Fungal
infections occur during moist conditions and fungicides are recommended in
the spring from the period of early bud break through bract fall and through
early leaf development. When fungicide
is required, use a labeled product containing propiconazole
or mancozeb. Flowering dogwood should
be planted in sites with good soil drainage and adequate organic matter. Partially shaded sites, such as those with
just morning sun are ideal. Plants
should receive a moderate fertility program, and should be mulched to
moderate fluctuations in soil temperatures.
Dead branches should be promptly pruned from the plant. |
Anthracnose on dogwood leaves |
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Control of Anthracnose Diseases
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1. |
Overall
tree care program. Use proper fertilization,
pruning, watering, and pest control practices to encourage vigorous plant
growth. This aids in general tolerance
of the effects of disease and in rapid re-foliation in years where disease is
severe. |
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2. |
Fungicide
applications. If significant damage occurs yearly and controls are justified,
properly applied fungicides may reduce damage from these diseases. High
pressure spray equipment will be needed for large tree applications, and this
typically requires the hiring of a professional tree care service. Fungicides
will not be effective unless they are applied before and during infection
periods. Typically, three applications are necessary, beginning in early
spring. |
Information obtained through the Ohio
State Extension Fact Sheet HYG-3048-96
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES