Sporulation of the fungus appears as a delicate, dense, white, cottony growth in the lesions. They eventually turn brown and die. Similar symptoms are seen on petioles, tendrils and young inflorescences, which, if attacked early enough, ultimately turn brown, dry up and drop. The young berries are highly susceptible. Infected berries of white cultivars may turn dull gray-green, while those of black cultivars turn pinkish red.
Infected berries remain firm, compared to ripening healthy berries, and drop easily.
Portions of the rachis or the entire cluster also may drop. Limited rainfall in spring and summer generally limits the spread of the disease in California. Surviving inoculum may be present in California at low levels and initially may have been introduced on plant material from outside of California. In most regions the fungus survives the winter mainly as oospores in fallen leaves. However, in California's generally mild winters, survival of the fungus in buds, shoot tips, and persistent leaves may be more important than in other grape-growing regions.