Flowering dogwood (Cornus florida L.) is used as an important ornamental tree in North America, Japan, and Europe. Since 1995, epidemics of powdery mildew caused by Erysiphe pulchra (Cooke and Peck) U. Braun & S. Takamatsu (syn. Microsphaera pulchra Cooke and Peck) have impeded production of flowering dogwood throughout much of the eastern United States. The fungus is an obligate parasite and g...