My husband has a trellis of grapes that we started from cuttings from a friend a few years ago. They have been doing pretty well until this year. The grapes sit pretty far from any other garden areas, so I did not notice the problem until we had lost most of the grapes.

Black rot had infected the vines. The grapes developed dark spots and then shriveled into what are called mummies. The leaves develop orangish spots. I had noted the grapes darkening from a distance, but I just thought they were ripening. Maybe if I had taken a good look earlier, I could have saved more grapes. When I did realize what was happening, I researched the problem to find a solution.

Black rot is caused by the fungus Guignardia bidwellii. Our warm, humid summer made the grapes more susceptible to this infection. Black rot can infect all parts of the vine. Look for lesions on the canes and tendrils. The organism will over winter in the mummified berries.

Sanitation is critical in control of the fungus. Remove and destroy the mummies, remove diseased tendrils from the trellis and, if possible, when pruning, leave only canes without lesions. In the spring, if only a few lesions appear on the leaves, remove these. Grapes planted in sunny areas with good air circulation are less susceptible. Keep areas below the vines free from weeds.

The use of fungicides is the most effective way to control black rot. For the organic gardener, the cultural practices in the last paragraph are the safest route. Copper and sulfur based fungicides are considered more organic, but are not as effective as other fungicides on the market. It is important when using any product to thoroughly read the labels, making sure it is meant for grapes and follow the directions. The vines should be sprayed every 7-10 days in the spring from prebloom to 3-4 weeks after bloom.

I was going to try my hand at making wine from my grapes, but maybe next year!

Reference: Midwest Small Fruit Management Handbook