Anthracnose of Shade Trees

Symptoms of anthracnose, primarily on ash and sycamore, have been evident on samples arriving in the Plant Disease Clinic. The disease may occur on sycamore, ash, maple, oak, walnut, linden, hickory, and other deciduous trees. Anthracnose is caused by a number of different but closely related fungi. Each fungus is specific to the host tree if affects.

In most cases, damage caused by anthracnose is minimal and does not seriously harm established shade trees. Symptoms vary from small, circular to irregular spots that are tan, dark brown, or black, to larger blotches that are usually associated with midribs and veins. When immature leaves are infected, these leaves may become distorted. Young leaves may die and fall from the trees. If a severe infection occurs early in the growing season and defoliation occurs, a new set of leaves may emerge. On sycamores, bud, shoot, and twig blight may also occur in addition to blighted leaves.

There are several strategies to follow when trying to decrease the severity of anthracnose:


  1. Clean up and destroy as many fallen leaves as possible. This will help reduce overwintering of the fungi.


  2. Prune the tree if feasible to removed diseased twigs and branches (primarily for sycamore anthracnose) and to open up the canopy for better air circulation.


  3. Maintain tree vigor with cultural practices such and mulching and watering as needed.


  4. Select species that are resistant or less susceptible to anthracnose.


  5. Fungicide control is rarely warranted because anthracnose usually does not seriously damage tree health.


Pm-1280, "Anthracnose of Shade Trees", gives further information on anthracnose and contains color photos of disease symptoms. This bulletin can be obtained from your local Extension office or from the Extension Distribution at Iowa State University (515)- 294-5247.


This article originally appeared in the June 9, 1995 issue, p. 84.


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