Description:

Black rot, a foliar and fruit disease of grapes is considered to be the most serious disease of grapes in all areas where it occurs, including Oklahoma. All of the new growth can become infected during the growing season. The greatest number of infections, however, occur during the spring.

Symptoms:

On leaves, the black rot disease appears in late spring on the upper surface as definite necrotic (dead) spots which are at first circular and red. Later, the spots are visible on both sides of the leaf. As the spots enlarge, their margins become black and the red spots turn brown. At this time the spots may be irregular in shape. After the spots cease growing, they may be about 1/4 inch in diameter. Also, small black dots, asexual fruiting structures begin forming. Infection spots (lesions) usually do not appear on fruits until after they are half grown. The first symptom is the appearance of very small whitish areas on developing green fruit. These are soon surrounded by a rapidly widening brown ring, giving a bird's eye effect. As the fruit rots, black sexual fruiting bodies begin to form. Later the rotted fruits become black, studded mummies.

Control:

Pruning of vines removes much infected tissue, but the pruning action causes old fruit mummies to fall to the ground, thus providing them an advantageous environment to stay wet for long periods, thus aiding spore production. Cultivation which throws soil over the mummies prevents release of spores. Weed control and proper pruning provide good air circulation, thus keeping foliage dry and protected from fungus infection. Many grape cultivars have some resistance but still require a few applications of recommended fungicide sprays during wet periods. Cultivars that have large fruits or mature early in the season are the most susceptible.

Please check the "Extension Agents' Handbook of Insects, Plant Disease and Weed Control".