Anthracnose caused by Gnomonia tiliae causes elongated light brown areas next to the veins. The spots may be anywhere on the leaf but are most often near the tip. The spots are bordered by a distinct black band. Severe infections defoliate the tree. The disease does not require chemical controls every year but repeated severe infections may justify spraying.
Leaf blight causes leaves to brown and fall. The early symptoms are round, brown spots with dark borders. The spots become numerous leading to leaf browning and drop. No chemical control is listed.
Several fungi cause cankers and dieback on branches and trunks. Remove infected branches as they occur and avoid wounding the tree. Fertilizing infected trees may help.
Powdery mildew forms a white coating on the leaves but is usually not serious. If control is needed, use benomyl.
Verticillium wilt causes dieback and death of individual branches or the entire tree. Keep trees healthy to prevent the disease. Fertilizing infected trees with high nitrogen fertilizers helps.