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.
Use benomyl according to label directions. Ash ring spot virus causes chlorotic green and reddish spots on the leaves. Leaves may also have ring spot in ring or line patterns. Infected trees may be stunted and dieback. Verticillium wilt causes branches of infected trees to wilt and die, eventually the entire tree may die.