Defoliation occurs when infection is severe. Sanitation is important in the prevention and control of this problem. Remove all diseased leaves. Spraying is seldom required. Trees which have been severely damaged by the disease should be given additional fertilizer to stimulate new growth.
Powdery mildew occurs on all groups of oaks.
Infected leaves have a faint indistinct spot on the upper leaf surface and a white to off-white powdery growth on the lower side. The fungus will most often be found along the veins and midribs of the leaf. It is normally observed in late fall. Infected leaves will be slightly disfigured in severe cases. Powdery mildew is seldom a problem on large individual trees.