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Anthracnose of Shade Trees

Susceptible Plants
Sycamore (Platanus), maple (Acer), ash (Fraxinus), oaks (Quercus), birch (Betula) and others

Description & Symptoms
Anthracnose refers to a group of fungal diseases that cause discolored spots on leaves and, occasionally, on other parts of a tree. These spots usually are tan, purplish, dark brown, or black and merge into dead areas that sometimes follow the leaf veins. Leaves, which may become curled and distorted, often drop prematurely to the ground. On sycamores, the disease often infects branches, causing girdling cankers and dieback.

Timing & Life Cycle
Anthracnose is most prevalent in cool, wet spring weather. Fungal spores overwinter on cankers on infected stems and fallen leaves. Dispersed by wind and rain in the spring, they land on young foliage. With sufficient moisture, the spores germinate, penetrate the leaf surface, and cause lesions. As the fungus grows, more spores are produced, reinfecting leaves.

Anthracnose rarely kills a tree or even seriously affects its health. In severe cases, a tree may defoliate, but a healthy plant usually will recover and grow a new set of leaves. Trees that are afflicted year after year are weakened, and extensive cankers also are damaging.

Treatment & Solutions
Fungicide treatments are not warranted and rarely provide complete control. Raking and disposing of diseased leaves help prevent a cycle of reinfection. Providing good air circulation also slows the disease because the fungus needs a moist leaf surface to germinate. Severely infected trees that have defoliated will benefit from adequate water and an application of nitrogen fertilizer.