Evaluating biological fungicides for grape powdery mildew management by tank mixing with low rates of sulfur

Biological fungicides, those with living organisms, are organic compliant but with variable efficacy. Under high disease pressure these products have been unable to adequately manage grape diseases such as grape powdery mildew (GPM). Biological fungicides were tank mixed with below-label-rate micronized sulfur (2.5lb/A in 2021, 2lb/A in 2022-2024) to improve GPM management over sulfur alone. The bacterial-based commercial products Actinovate, Aviv, Double Nickel, Lifegard, Serenade ASO, Serifel, and Theia were evaluated on small plots of Chardonnay. All fungicide treatments resulted in significantly lower cluster severity and leaf incidence Area Under Disease Progress Curves (AUDPC) than non-treated controls. The Theia + sulfur mix resulted in significantly lower cluster severity by 30.6% and 38% when compared with sulfur alone in 2022 and 2023, respectively. The Theia mix also resulted in significantly lower AUDPCs than sulfur alone in 2022 and 2023. In 2021, Serenade ASO + sulfur mix resulted in significantly lower cluster severity by 16.7%-19.7% than sulfur alone. In 2024, GPM severity on clusters was significantly lower for Double Nickel or Serifel + sulfur tank mixes compared to sulfur alone. A Double Nickel + Humax tank-mix tested in 2024 resulted in a significantly lower AUDPC value than sulfur alone. All other tank mix treatments resulted in AUDPC values that were not significantly different from use of sulfur alone. Double Nickel, Serenade ASO, Serifel and Theia augmented GPM control over sulfur alone and could offer grape growers alternatives for GPM control.