Sycamore anthracnose is the only serious disease affecting sycamore and plane trees. The disease is common throughout the state where sycamores are grown.

The disease can appear as soon as the leaves emerge from the buds in the spring. The most characteristic symptom on young leaves is a crinkling and browning of the leaves. Entire younger leaves may be killed and then fall. These symptoms are very similar to those caused by late spring frost injury.

Later, after the leaves have developed, tan-colored leaf lesions characteristically extend along the veins. All leaf tissues, however, can show infection under some conditions. Large, irregular lesions can also be formed on leaf margins. Infection of the leaf petiole may occur, and leaves will fall even though no symptoms can be seen on the leaf. A severely infected tree may be infected and defoliated several times in a single season.

Small twigs and branches may also be affected, and cankers may eventually girdle and kill the infected branch. This will result in the production of many small shoots from the area just below the girdled portion of the branch, giving that part of the tree a bushy appearance. Sycamore blight is caused by the fungus Apiognomonia veneta. Masses of spores are produced on cankers and infected leaves. Spores are spread by rain and wind to healthy leaves, buds, and twigs where new infections can start. The fungus overwinters on fallen leaves and twigs, and in branch and twig cankers.

Control

Cultural. Fallen leaves and twigs should be raked up and destroyed. When possible, diseased branches and twigs should be pruned out and destroyed. These operations remove much of the overwintering stage of the fungus, thus limiting the number of spores being produced which can cause new infections. Care should be taken to sterilize pruning shears in rubbing alcohol or other disinfectant after pruning infected twigs and branches.

Adequate fertilizer and water should be applied to maintain tree vigor and stimulate new foliage which will replace that which is lost due to disease.

Sycamore and plane trees vary in their susceptibility to anthracnose. The Oriental plane tree is resistant while the native sycamores are susceptible. Hybrids of these trees vary in their susceptibility. The original London plane tree, an Oriental hybrid, is resistant, but seedling offspring from this clone vary in their susceptibility. Thus, a wide variety of disease reactions are often noticed between trees growing in the same vicinity. However, resistant clones that are vegetatively propagated, such as "Bloodgood," "Columbia,'' and "Liberty" maintain their resistance.

Chemical. Contact your county Extension office for information on currently registered efficacious fungicides.

By Ralph S. Byther, Ph.D., Extension Plant Pathologist (retired), WSU Puyallup, and Otis C. Maloy, Ph.D., Extension Plant Pathologist (retired), WSU Pullman. Reviewed and revised by Carrie R. Foss, M.S., Diagnostic Plant Pathologist, WSU Puyallup.

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College of Agriculture and Home Economics, Pullman, Washington.

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