Caleb Slemmons, National Ecological Observatory Network, Bugwood.org
Symptoms and Disease Cycle
Botrytis blight is caused by the fungus Botrytis cinerea, which overwinters on infected plants. Under favorable conditions, the fungus can infect blossoms, twigs, and fruit. Tips of infected shoots will die back and turn brown to black. Infected blossoms appear water soaked and turn brown, and the discoloration can spread down the twig. This blossom blight stage causes the most loss. Blighted blossoms often cling to clusters. Immature fruits shrivel and turn a bluish purple, whereas ripe, mature fruits become tan. In damp weather, all infected plant parts become covered with the characteristic "gray mold" of the fungus. Spores of the fungus are disseminated primarily by wind.
Cultural practices that improve air movement, such as pruning, aid in the control of blight and fruit rot. Avoid excessive use of nitrogen fertilizer in the spring because rapidly growing tips are more susceptible.