Insect
and Disease Fact Sheet Compliments of New Century
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Leaf Blight of Hawthorn
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Symptoms Leaf
blight is a serious disease of a few very susceptible English hawthorn cultivars.
Most other hawthorn species and cultivars are resistant or are not seriously
affected. The
disease is first evident as small, angular, reddish-brown spots on the
leaves. The spots have irregular margins and coalescence of spots often
occurs resulting in larger irregular diseased areas. Diseased leaves yellow
and fall prematurely. Sometimes, spots may be more prevalent near the margins
of the leaves. When conditions are favorable for disease development,
extensive defoliation occurs. It is usually mid-summer or after before the
disease becomes prevalent. Small, black, raised dots develop in the center of
the spots. These are the spore masses of the causal agent. They are
especially evident when the leaves are wet. |
Leaf blight symptoms on hawthorn leaf. |
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Defoliation of hawthorn caused by leaf blight. |
Causal Fungus Leafblight of hawthorn is caused by the fungus, Entomosporium thuemenii (Diplocarpon maculatum). The
fungus survives from one year to the next in fallen diseased leaves and in
inconspicuous stem spots. During May and June, spores are produced on these
over wintered leaves. These spores are spread by splashing rain and initiate
the disease on the current season's foliage. As the leaf spots develop, new
spores are formed on the spots and rapidly spread the disease. Wet weather is
favorable for rapid development because splashing water carries spores, and
persistent water drops favor spore germination and infection. Control Plant resistant varieties Washington
hawthorn types are resistant to this disease. English hawthorn types are
susceptible and are commonly infected. Although Washington types are
resistant to leaf blight they are susceptible to rust diseases. If hawthorn
rust is a serious problem in your area, it may be best to select plants other
than hawthorns for landscape plantings. Sanitation Since
the fungus over winters in the fallen diseased leaves, raking and destroying
all leaves will help to manage leaf blight, but will probably not result in
complete control. |
Protection with Fungicides
Leafblight can be prevented by spraying with fungicides. Control
through use of fungicides depends on proper timing of the sprays. Based on
presently available information, spraying at 10 to 14 day intervals from bud
break through early July has given good control. Additional applications may be necessary
during rainy seasons or when good control was not achieved with the earlier
sprays.
Information obtained through the Ohio State Extension Factsheet HYG-3039-96
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES