Field evaluation of bio-fungicides to control powdery mildew (Erysiphe necator) of wine grapes in California

Tuesday, August 5, 2025

4:45 PM - 5:00 PM HST

Location: Room 313 C

Presenting Author(s)

SZ

Shijian Zhuang (he/him/his)

Viticulture Farm Advisor
University of California, Riverside
Fresno, California, United States

Author(s)

EM

Edgar G. Monterroso

California Polytechnic State University-San Luis Obispo
San Luis Obispo, California, United States
QS

Qun Sun

California State University, Fresno
Fresno, California, United States
MF

Matthew W. Fidelibus

University of California, Davis
Parlier, California, United States
PR

Philippe E. Rolshausen

Cooperative Extension Specialist
University of California, Riverside
Riverside, California, United States
SD

Shunping Ding, Ph.D

Associate Professor
California Polytechnic State University-San Luis Obispo
San Luis Obispo, California, United States

Abstract Text: Grapevine powdery mildew caused by Erysiphe necator is one of the most important fungal diseases in CA grape production. Growers are interested in using biofungicides because of the tightening of state regulations and high risk of fungicide resistance in the pathogen populations. During 2023 and 2024, we conducted two bio-fungicide field trials on Chardonnay grapevines located in the Central Coast and San Joaquin Valley of California, respectively. At each location, two experimental blocks were selected. Weather stations were placed in the vineyards prior to budbreak to monitor powdery mildew disease pressure using the Gubler-Thomas risk index model. Fourteen treatments, including three biofungicides (Bacillus subtilis, Streptomyces lydicus, and an extract of Reynoutria sachalinensis) applied at various intervals (weekly, biweekly, or based on the powdery mildew risk index), bio-fungicides in rotation with synthetic fungicides, a grower standard program with only synthetic fungicides, and a non-treated control, were applied to grapevines starting at bloom time and until veraison. Disease incidence and severity were rated biweekly until veraison; yield and berry chemistry were measured at harvest. Standalone bio-fungicides demonstrated higher disease control efficacy when applied weekly. Bio-fungicides provided effective disease control under low disease pressure (2024) but were less effective when pressure was high (2023). Overall, programs rotating bio-fungicides and synthetic fungicides achieved the best disease control, comparable to synthetic fungicides-only treatments.