Anthracnose Disease Of Shade Trees 7-07 Fs2401

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Anthracnose Disease of Shade Trees Leaves of maple, ash, sycamore, plane tree, beech, birch, white oak, elm, horse chestnut, walnut, and to a lesser extent many other tree species may be affected by the fungal disease anthracnose. Infection occurs during cool, wet weather in the spring, as leaves are expanding. Expanding shoots, flowers and fruit may also be infected. Symptoms: Anthracnose typically causes irregular, brown-black blotches on affected leaves. Blotches often follow the leaf veins, and may blight the entire leaf. Severely affected leaves may fall from the tree. If weather conditions are particularly favorable for infection, the tree may be defoliated. Expanding shoots may be directly infected by fungal spores, but more often shoot infections occur when leaf infections spread down the petiole. If a shoot is girdled by an infection, growth beyond the girdling wilts and dies. Cause: Fungi of the genus Discula and several related species are responsible for anthracnose disease. These fungi overwinter on dead infected leaves on the ground, and to a lesser extent on infected twigs on the tree. In early spring they sporulate, leading to new infections while the weather is cool and moist. Spores can then be produced on the newly infected tissue and spread to further leaves, shoots and even from tree to tree. Once weather conditions change in late spring and early summer, the disease is halted. Impact: Trees that are significantly defoliated due to anthracnose will put on a second flush of growth as the season progresses. Anthracnose rarely affects the second set of leaves because the weather is no longer favorable for infection. Even when trees are defoliated on an annual basis anthracnose infection rarely has a negative impact on the overall health of the tree. Control: Since this disease ceases as the weather becomes warmer and drier, in most cases there is no need for control. Removal and discarding (or composting) of fallen leaves helps to reduce the infection potential for the following year. Fungicides are not recommended for homeowner application for anthracnose because the disease does not affect the overall health of the tree. Also, once symptoms become obvious it is already too late to treat. Without special spray equipment it is difficult to effectively spray tree foliage. If the disease is a persistent problem and the tree is in a prominent site in the landscape so that the symptoms are aesthetically unacceptable, a fungicide spray program may be initiated at budbreak. For large trees, a tree-care professional should be consulted. If you choose to treat a smaller tree, the following chemicals are registered for homeowner use on the following hosts; apply according to label directions. London plane, Sycamore (Platanus): chlorothalonil, copper, flutalonil, mancozeb, Basicop, Kop-R-Spray, Liquid Copper Fungicide, or Camelot Maple (Acer): flutalonil, mancozeb, Dexol Bordeaux, Basicop, or Camelot Oak (Quercus): chlorothalonil, copper, flutalonil, Dexol Bordeaux, Basicop, Kop-R-Spray, Liquid Copper Fungicide or copper salts of fatty & rosin acids Revised 4/29/96, 5/03, 3/04, 6/07 FS 2401 Building Strong and Vibrant New York Communities Cornell Cooperative Extension in Monroe County provides equal program and employment opportunities.