Evaluation of Fungicides for Control of Powdery Mildew and Botrytis Bunch Rot of Grape in the Central Coast of California, 2024

Grapevine powdery mildew is caused by the fungal pathogen Erysiphe necator, which infects all green tissues of the vine. Infected tissues exhibit a whitish, powdery fungal growth and may develop chlorosis, eventually leading to necrosis. Another common disease in grapevines is Botrytis bunch rot, caused by Botrytis cinerea. The pathogen inoculum enters grape clusters early and initiates infection as the bunches close and mature. The rot typically begins inside the cluster, with infected areas showing characteristic gray, fuzzy fungal growth. Both are polycyclic diseases that require repeated fungicide applications for effective management. They significantly reduce yield and fruit quality in grape production. This report assessed the effectiveness of conventional, biological, and experimental products, applied individually or as part of a treatment program, for managing powdery mildew and Botrytis bunch rot. The trial was conducted in 2024 on ‘Chardonnay’ grapevines in San Luis Obispo, CA. The findings can assist growers in selecting and implementing effective fungicide programs for disease control in their vineyards.