From BugwoodWiki

powdery mildew Photo by Edward L. Barnard, Florida Department of Agriculture and Consumer Services, Bugwood.org Taxonomy Kingdom: Fungi Phylum: Ascomycota Class: Leotiomycetes Order: Erysiphales Family: Erysiphaceae Genus: Microsphaera Species: penicillata Scientific Name Microsphaera penicillata (Wallr.) Lév. Scientific Name Synonym Erysiphe penicillata (Wallr.) Fr. Microsphaera alni (DC. ex Wallr.) G. Winter

Author: Paul Bertrand, University of Georgia

Symptoms

Powdery mildew first appears as dusty white spots, 1/8 - 1/4 inch in diameter, on nuts or leaves. The symptoms are usually most obvious on the nuts which may become completely covered with dusty white growth. Leaflets attacked early in the season often show large faded areas. Tissue development in these areas may cease causing the leaflets to become wrinkled and misshapened with age (Figure 4). Nut infections (Figure 5) during June and July can lead to size reduction. Nuts covered with mildew retain the potential to fill properly even when reduced in size.

Most varieties can be attacked by powdery mildew, but Pabst, Wichita, Desirable and Farley are especially susceptible. If any of these varieties are present, they can be scouted for powdery mildew.