Highlights Black Rot of Grape Black rot of grape is caused by the fungus Guignardiabidwellii . On leaves, the first symptoms are small, yellowlesions. These spots develop into brown lesions that aresurrounded by dark irregular margins. Purple to black sunken lesions may also develop on youngshoots and stems. Fruiting structures are also evident in theselesions.
Fruit are susceptible to infection.
First, smallbrownish spots appear on fruit. These spots enlarge very quickly,often within a few days. The infected fruit then shrivel andbecome hard and black. These diseased fruit are referred to asmummies. The black rot fungus can survive the winter in mummifiedberries and also in stem lesions.