Black rot is the most widespread fungus disease of grapes.
In warm humid weather this disease can cause complete crop loss. The black rot fungus can infect all green tissues of the vine, but the fruit are the most severely damaged. All cultivated varieties of grapes are susceptible to infection by the black rot fungus. Symptoms Symptoms of black rot first appear as small reddish - brown circular spots over the upper surface of the leaf. As the spots enlarge a black border forms around the margin.