Unlike most other fungi, powdery mildew spores do not require water on the leaf surface in order to germinate and then infect a leaf. Powdery mildew fungi need live tissue to grow and reproduce. In the following year, new infections may begin from the infected leaf litter. Some species of powdery mildew may overwinter in the buds. Because powdery mildew occurs so late in the season, it may not reduce the long-term health of trees and shrubs.
Infections tend to be unsightly and of cosmetic concern.
Prevention Adequate plant spacing will help to increase the air circulation around plants to discourage disease development. Gardeners should avoid placing plants in a damp, shady corner with poor air circulation that will promote powdery mildew. The cleanup of infected leaves may help to reduce disease inoculum. Resistant Varieties Gardeners should first consider the use of species or varieties that are resistant to powdery mildew. The following is a partial list of varieties reported to be resistant.