Control

In most cases, control of anthracnose is unnecessary because the disease is usually not damaging to the long-term health of trees. When control is desired, various techniques can help reduce the severity of the disease.

Raking and destroying fallen leaves and twigs and pruning out dead branches on the tree will help reduce the overwintering population of anthracnose fungi. Pruning will also increase air circulation in the canopy, reducing the time that wet conditions, which favor fungal infection, are present on leaf surfaces. Healthy trees are more likely to recover from a severe anthracnose attack than are stressed trees. Mulching and watering during dry periods will help keep trees healthy.

When selecting trees to plant, species or cultivars that are less susceptible to anthracnose should be chosen. London planetree is much less susceptible to anthracnose than American sycamore. Northern red and pin oaks are usually less severely affected than white oak species, and green ash is relatively resistant compared to white ash. At planting time, trees should be spaced far enough apart to allow good air circulation when the trees are fully grown.

Chemical sprays to control anthracnose are rarely justified except when the disease occurs in stressed or recently transplanted trees, or when the disease causes repeated defoliations. Fungicides labeled for control of certain anthracnose diseases include chlorothalonil (Daconil 2787), thiophanate-methyl (Clearys 3336, Fungo 85), mancozeb (Dithane), lime-sulfur, Bordeaux mixture, and other copper fungicides (such as Tenn-Cop 5E). The first spray should be applied in the spring when buds begin to swell, followed by two to three additional sprays at 10- to 14-day intervals. For walnut anthracnose, the first application should be made when the leaves begin to unfold, followed by additional weekly sprays as needed, especially if rainy weather persists. Read label directions for more information on timing and application.

Another fungicide, thiabendazole (Arbotect), is labeled for systemic injection into tree trunks for the control of sycamore anthracnose. Injections should be made by a professional arborist in the late summer or fall before leaf drop for control of anthracnose infections the following spring. Although thiabendazole injections give good control, this treatment is not recommended for use on an every-year basis because of the trunk wounding caused by the application technique.

The symptoms caused by K. apocrypta appear following infection during cool, wet weather throughout the spring and summer. Infected young leaves and shoots may shrivel and turn black. On more mature leaves, red, brown, tan, or black lesions develop that may or may not be associated with leaf veins. Leaves may become crinkled or otherwise deformed. Lesions often coalesce and kill large areas of leaf tissue. In severe cases defoliation may occur.