On stems, black rot appears as irregular or sometimes diamond-shaped, somewhat sunken, tan brown lesions also with scattered pycnidia. On the fruit, symptoms start as light brown soft spots which rapidly enlarge to involve the entire berry. Affected berries then shrivel into black, wrinkled mummies which either drop to the ground or remain in the cluster. As with leaf spots and stem lesions, black rot mummies are covered with pycnidia. The fungus survives the winter in mummies both on the vine in the trellis and on the ground, and in fallen leaves and stem lesions.
Spore production starts in the spring as temperatures increase and wet weather prevails.
Primary infection takes place if plant surfaces stay wet long enough for spores to germinate and penetrate host tissues. After infection, symptoms generally take about 2 weeks to develop. Once the fungus has become established in susceptible tissue, it starts producing secondary spores which, in turn, are capable of infecting. This cycle of spore production and infection continues the rest of the season, except when the environment becomes limiting. A single ascospore or conidium can cause a primary leaf infection.