Look for
Leaves - Irregularly shaped, reddish brown spots with black borders. These spots often develop a ring of small black dots on the inside margin.
Shoots - Spots also may appear on young shoots, petioles, stems and tendrils.
Fruit - Small, round, brownish spots on half-grown berries quickly enlarge and rot the grapes, turning them into black, shriveled mummies.

 
Ecology
The black rot fungus survives the winter in mummified fruit on the vine or on the ground, and in diseased spots on the vines. Spores, released in wet weather during the next spring to mid-summer, spread the disease.

Management checklist
Sanitation - Remove and destroy all mummies. Bury or rake out fallen mummies and leaves. Prune out diseased vines and tendrils. If only a few leaf spots appear in the spring, remove these leaves.
Site selection - Plant grapes in sunny, open areas with good air movement.
Planting design - Orient the rows parallel to the prevailing wind direction to encourage rapid drying.
Weed control - Tall weeds hold in moisture, so remove weeds to speed drying.
Fungicides - If black rot is causing  problems, a program of regular fungicide spray may be needed. Fruit can't be infected after it begins to turn color during ripening. Sprays for black rot are applied from bud break until fruit begin to change color.