Evaluation of Fungicide Programs for the Control of Powdery Mildew on Wine Grapes in California, 2024

Grape powdery mildew is a polycyclic disease caused by Erysiphe necator that reduces both crop quality and yield. It is considered one of the most economically important grape diseases worldwide. All green tissues of the vine are susceptible to infection if management strategies are not properly implemented. Initial symptoms appear on leaves as chlorotic spots on the upper surface. Shortly thereafter, signs of the pathogen emerge as a white to grey, web-like mycelium on the lower leaf surface. On fruit and rachises, the pathogen develops 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 in grapes. The trial was conducted in 2024 in Davis, CA, in a 13-year-old Vitis vinifera ‘Chenin Blanc’ vineyard. Results from these trials will inform U.S. grape growers in developing effective management programs for this disease.