Young leaves, young twigs, and flower buds are covered with a thin layer of grayish white powdery material. Infected leaves may be distorted and curled, and many may turn yellow or purplish and drop off. New growth is often stunted, and young canes may be killed. Badly infected flower buds do not open properly. In late summer, tiny black dots spore-producing bodies) may be scattered over the powdery covering like ground pepper.
Apply a fungicide labeled for this disease, following label directions. Rake up and destroy leaves in the fall.