F is optimum, however, this fungus can germinate over a wide range of temperatures. Moisture is necessary for germination. Leaves are susceptible for about 1 week after they unfold. Black rot is generally considered an early-season disease since all green tissue is susceptible and fruit is susceptible up until veraison. Symptoms on fruit usually will occur prior to veraison.
Infected berries turn from light brown to dark brown, then shrivel and turn hard and black.
The hard black mummies remain firmly attached to the cluster. Tiny black fruiting bodies can also be seen on the shriveling berries and on the hard, black mummies. Infected fruit will contaminate wine. Upper leaf surfaces develop yellowish lesions, while lower surfaces develop a white, downy sporulation, especially along veins. Severe infection leads to defoliation.