Evaluation of Fungicide Programs for the Control of Powdery Mildew on Grapevines in California, 2023

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. All green tissues of the vine are susceptible and may be infected if management strategies are not properly applied. Initial symptoms of powdery mildew appear on leaves as chlorotic spots on the upper leaf surface. Signs of the pathogen appear shortly as a white to grey webby mycelium on the lower leaf surface. 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 2023 in Davis, CA, on a 12-yr-old Vitis vinifera ‘Chenin Blanc’ vineyard. Results from these trials will help advise U.S. grape growers in improving management programs for this disease.