Irregular spots appear on the leaves, which are framed by a dark line. Shoots, stems and leaf stalks can also show symptoms of these spots. If leaf stalks are affected the whole leaves will dry. Grapes will show grey discolorations in the first beginning, which then turn to reddish-brown or violet spots. The fruit will become deformed and eventually be shriveled and black mummified.
The damage is caused by the fungus Phyllosticta ampelicida. The pathogen overwinters in infested shoots or fruit mummies on the grapevine or the soil. The spores will be ejected by light rainfall and then dispersed via wind. Optimal growth conditions are met at 25°C and 6 hours of constant leaf wetness. The fungus prefers warm and humid weather. Reduced fruit yield.
Immediately after blooming stage you can spray Bacillus thuringiensis.
Chemical applications are done in a preventive manner. Start spraying roughly two weeks before bloom with captan + mycobutanil or mancozeb + mycobutanil. Just before the blossoms open you can also use carbaryl or imidcloprid. Post-bloom spray mancozeb + mycobutanil, imidacloprid or azadirachtin. Ten days after bloom you can also apply a mixture of captan and sulfur on your vines. Because most grape varieties become resistant to the infection three to four weeks after bloom, chemical sprays should be avoided at that time.