Fungus Diseases in Grapes

Types

• Bunch rot, powdery mildew, Armillaria root rot, canker, crown gall and Pierce's disease are among the fungal infections that can damage grapes.

Causes

• Bunch rot is caused by the fungus Botrytis cinerea; powdery mildew by the fungus Erysiphe necator; and canker disease by Botryosphaeria, according to the University of California Agriculture Department.

Facts

• "Powdery mildew is among the worst grapevine diseases in California," according to UCA. The fungus is prevalent throughout all grape-growing regions of the state.

Identification

• Powdery mildew can be identified by the "dust-like spores" that cover the leaves of infected vines, while "bunch rot infects grape berries through wounds or even directly though the skin," according to UCA.

Features

• It can take time for symptoms of Pierce's disease to appear on infected vines. For example, a vine infected in spring may first show signs of water stress in midsummer, says the UC Integrated Pest Management Program.

Prevention/Solution

• Bunch rot primarily infects vineyards in moist coastal areas. "Leaf removal to control bunch rot and improve grape quality was developed in the 1980s," according to UCA. Removing leaves around clusters allows the grape berries to dry more quickly after rainfall, decreasing the proliferation of bunch rot infection.