The asexual stage (the reproductive stage that does not require mating) looks so very different from the sexual stage (the reproductive phase that requires mating) that early scientists thought they were totally different organisms not related to Apiognomonia. It is now known that some of the fungi previously named Colletotrichum, Gloeosporium, and Discula are just the asexual stage of Apiognomonia.
With a magnifying glass, examine the underside of infected leaves for pimple-like fungal fruitings structures, especially along the leaf veins.
Examine dead twigs near the ends of branches for pimple-like fruiting structures peppering discolored, slightly sunken bark areas.
Cool weather (50° to 55° F, average daily temperature) during leaf bud break and emergence greatly favors disease development whether it is wet or dry. Although wet weather tends to favor this disease, temperature is the most important factor. If daily temperatures average above 60° F at bud break, anthracnose is usually not severe.
The fungus survives the winter dormant primarily in cankers on infected branches and twigs. To a small extent, the fungus also survives in fallen leaves. Wind carries the fungal spores from the cankers to developing leaf and twig tissue. Infected young twigs are girdled and killed. The fungus forms new spores on the infected leaves and twigs. These spores are then blown or splashed to nearby foliage where they germinate, penetrate and cause additional spots if weather conditions are favorable. Infected leaves shrivel and fall.
Dogwood anthracnose
Ash anthracnose
Oak anthracnose
Sycamore anthracnose
Prepared by Gary W. Moorman, Professor of Plant Pathology
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