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Fungus Attacks Maple Trees

From the UW-Extension

Numerous homeowners have reported the leaves of their maple trees turning brown and falling from the tree. The problem is anthracnose, a fungal leaf disease. Anthracnose is the name of several common fungal diseases that affect the foliage of woody ornamentals in Wisconsin. Trees that are most commonly and severely affected by anthracnose include ash, maple, white oak, sycamore, and walnut.

• What does anthracnose look like? Symptoms of anthracnose vary from host to host, but in general, include irregular spots, and dead areas in leaves that often follow the veins of the leaves. Affected tissue can vary in color, but is often tan or brown. Severely affected leaves often curl and may fall off. In some tree species, such as sycamore, twigs can also become infected.

• Where does anthracnose come from? Anthracnose is caused by several fungi (many in the genus Gloeosporium) that survive in leaf litter. These fungi are host specific. The anthracnose fungus that infects one type of tree (e.g., ash) is not the same one that infects another (e.g., maple). However, if you see anthracnose on one tree, then weather conditions (typically cool and moist) are favorable for development of the disease on many types of trees.

• How do I save a tree infected with anthracnose? Don’t panic! For many trees, anthracnose is a cosmetic disease, making the tree look a little ragged, but not killing the tree. If however, a tree has been defoliated by anthracnose for several years, or it is a tree, such as sycamore, where twig infections can occur, then you may want to use a fungicide for disease control. Fungicides containing chlorothalonil, copper, dithiocarbamates, or mancozeb are registered for use against anthracnose. For most products, three treatments are needed for adequate control: one at bud break, one when leaves are half expanded, and one when leaves are fully expanded. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.

• How do I avoid problems with anthracnose in the future? You can reduce the number of spores that cause anthracnose infections by removing and discarding fallen, infected leaves.

For more information call 920.746.2260.