Evaluation of Fungicide Programs for the Control of Summer Bunch Rot on Grapevines in California, 2023

Summer bunch rot, caused by multiple fungal pathogens such as Botrytis cinerea, Aspergillus spp., Rhizopus spp., Alternaria spp., Cladosporium spp., and Penicillium spp., is an economically important disease that affects grapes ( Vitis vinifera), especially in warmer areas of the San Joaquin Valley in California. Symptoms and signs include masses of black, brown, or green spores on the surface of the berries; leakage of berry juice; hairline cracks in the berry skin; watery discoloration of berries; general berry breakdown; and the presence of vinegar flies. This report evaluates the efficacy of experimental and registered biological and conventional fungicide programs for the management of summer bunch rot on grapes. The trial was conducted in 2023 in Clarksburg, CA, on an 11-year-old ‘Riesling’ vineyard. Results from this trial will help advise U.S. grape growers in improving management programs for this disease.