A leaf and twig spot disease on willow, caused by the fungus Marssonina, can result in unsightly foliage on many kinds of willow. The disease can be especially severe on young willow leaves and stems soon after bud break in the spring. It is favored by moist weather, and can remain a problem during summer when weather is moist. Although the disease can be aesthetically damaging because of the unsightly appearance of the foliage, generally there is no significant damage to the growth of the tree.

Symptoms of the disease on the leaves and twigs appear as rather small, brownish to black, irregularly shaped spots. These spots, or lesions, generally have small white centers and may occur on either side of the leaf, depending on environmental conditions. If the spot is larger, there may be several white specks within it. The white specks contain thousands of spores, and are most often seen during moist weather. Lesions may be darker on the twigs than on the leaves. Twig lesions may result in death of the twigs.

Good sanitation procedures, such as pruning out dead and diseased twigs and raking up fallen leaves, can help control this disease to some extent. However, pruning large trees is generally impractical, if not impossible. Raking up and destroying fallen leaves throughout the growing season, and especially in the fall, is important.

No fungicides are specifically registered for use against this disease on willow. Fungicide applications in the spring to control twig blight (venturia) will also control this disease (see Cooperative Extension's Pacific Northwest Plant Disease Control Handbook).

Prepared by Roy M. Davidson, Jr., former research technologist, and Ralph S. Byther, retired Extension plant pathologist, Puyallup.

College of Agriculture and Home Economics, Pullman, Washington

Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information; no endorsement is intended. Revised from and replaces EM4043. March 1994. Subject code 356. A. EB1778