More information about growing dogwoods is available in HGIC 1010, Dogwood . A fungus that attacks leaf surfaces and tender shoots causes powdery mildew. New growth is covered with a fine, white, powdery coating, typically on the upper surfaces of the leaves. Infected leaves exhibit marginal leaf scorch, dead patches, reddish discoloration, yellowing and premature defoliation. Spores are spread by wind to surrounding dogwood plants.
Powdery mildew is most common in dense, shady areas where the air circulation is poor.
Warm, dry days and cool, damp nights favor disease development. Infection that begins early in the season can be devastating, and the use of fungicides may be warranted. Cultural controls should be the first line of defense. Begin by raking up and destroying all fallen leaves. Prune out dead and infected branches and twigs.