|Black Rot Infected Grapes
(Photos by John Jaworski, Dearborn County Extension Educator)
|Grape Leaf with Black Rot Spots
(Photo courtesy of Paul Pecknold)
Black rot of grape, caused by the fungus Guignardia bidwellii, is the most common disease of grapes in Indiana. Initial symptoms appear on leaves as small, yellow lesions. These spots enlarge becoming reddish-brown with dark irregular margins. Fungal fruiting structures form within these spots and appear as small, black dots. Purple to black, sunken lesions may also appear on young shoots and stems. Symptoms on fruit appear when the grapes are half grown. First, small brownish spots appear on fruit. These spots enlarge very quickly, rotting the entire berry within a few days. The infected fruit shrivels, becomes hard, black, and wrinkled. These shriveled, infected fruits are called mummies.
Management of black rot focuses on cultural practices and the use of fungicides. Sanitation is extremely important for controlling this disease. The fungus survives the winter in the mummified berries and in stem lesions. Therefore, as leaves or fruit drop, rake and discard fallen leaves and fruit. Remove mummified grapes and infected canes. During wet spring weather, fungal spores are carried to young tissue where infection occurs. To reduce the spread of the disease, plant grapes in a sunny open area with good air movement. A preventive program of fungicide sprays, beginning shortly after bud break and continuing until the fruit begin to develop color, can help to suppress black rot.
For more information on this disease, refer to:
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Last updated: 25 June 2001/tlm.
The Plant & Pest Diagnostic Laboratory at Purdue University.