The disease is rarely serious enough to warrant chemical control. A number of fungi cause leaf spots on ash. The disease is worse in wet years and is partially controlled by gathering and disposing of diseased, fallen leaves. Anthracnose, caused by Gloeosporium aridum, is also called leaf scorch and leaf spot. Infected parts of the leaves turn brown, especially along the margins.
Infected leaves fall prematurely.
Rake up and destroy infected leaves. Canker diseases cause branch dieback and death of the tree when the trunk is infected. There is no chemical control for canker diseases. Try to keep trees healthy with regular fertilization. Powdery mildew makes a white coating on the leaves.