Wet spring conditions and falling ash leaves should bring to mind a common disease problem - anthracnose. Samples of ash anthracnose from across the state have been arriving daily in the Plant Disease Clinic.
Leaflets show brown to black blotches or spots. These spots commonly start at the margin and develop to the midvein. The leaflets tend to curl toward the blighted area. Spots may also occur on the leaf tips. Infected leaves often drop prematurely, with the lowest branches usually showing the most defoliation.
Fortunately, damage from anthracnose is usually minor. A tree may lose a large portion of its foliage, but produce a second flush of leaves later in the spring. Repeated loss of leaves from the disease year after year, however, can weaken ash trees and predispose them to other diseases, insects, or environmental stresses.
There is no single management practice for the control of ash anthracnose. Raking and removing as many fallen leaves as possible in the fall can help reduce the overwintering population of anthracnose fungi. A number of fungicides are labeled for control of anthracnose, but their use is seldom justified since the disease does not seriously damage tree health.
Anthracnose also occurs on other shade tree species such as oak, maple, and walnut. However, the disease is caused by different fungi on each of these tree species. For instance ash anthracnose cannot spread to maple.
More information on anthracnose can be found in Pm-1280 "Anthracnose of Shade Trees". This bulletin is available from your local county Extension office from the Extension Distribution Center , 119 Printing and Publications Building, Iowa State University, Ames, Iowa 50011-3171.
This article originally appeared in the May 21, 1999 issue, p. 62.
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