As the spots enlarge a black border forms around the margin. Lesions may also appear on young shoots, cluster stems and tendrils. The lesions are purple to black, elongated and sunken. The small black fruiting structures are scattered over the lesion surface. Fruit symptoms often do not appear until the berries are half grown.
Infection appears as a small whitish spot that is soon circled by a brown ring.
The ring enlarges rapidly, rotting the entire berry in a few days. The diseased berry shrivels, becoming small, black and hard. The final stage is a mummified berry, with its surface covered with the tiny black pycnidia. The mummies typically remain attached to the cluster. Cause of Black Rot Grape black rot is caused by the fungus, Guignardia bidwellii .