Evaluation of fungicide programs for the control of powdery mildew on wine grapes in California, 2025

Powdery mildew is caused by Erysiphe necator; this polycyclic disease of grape causes reductions in crop quality and yield and is considered one of the most economically important diseases of grapes worldwide. Signs of the pathogen appear as a white to grey webby mycelium that can develop on both leaf surfaces. On fruit and rachises the pathogen appears as white powdery masses that may colonize the entire cluster surface. This report evaluates the efficacy of experimental and registered biological and conventional fungicide programs for the management of powdery mildew on grapes. The trial was conducted in 2025 in Davis, CA, on a 14-yr-old Vitis vinifera ‘Chenin Blanc’ vineyard. Results from these trials will help advise U.S. grape growers in developing management programs for this disease.