Edgar Godoy-Monterroso,* Shunping Ding, Marco Fernandez, Quinn Cahoon, Shijian Zhuang, and Qun Sun
*Department of Viticulture and Enology, California Polytechnic State University-San Luis Obispo, Cal Poly 1 Grand Ave, San Luis Obispo, CA, 93407 (egodoymo@calpoly.edu)

Biofungicide efficacy in grapevine disease management is enhanced by selecting the right active ingredients and modes of action, optimizing application timing and understanding the pathogen’s biology, then integrating them properly into fungicide programs. The efficacy of biopesticides in vineyard production is influenced by local climate and environmental conditions. The objective of this study was to investigate the efficacy of biofungicides applied at different intervals in controlling powdery mildew and Botrytis bunch rot, and their effect on grape quality. The study was conducted in the San Luis Obispo Coast AVA on mature Chardonnay vines. Twelve fungicide programs were designed, with three biofungicides containing different active ingredients and modes of action, application intervals, and integration strategies. A grower-standard program and an untreated control were also included in the experiment. Fungicide applications started at bloom in May 2023 and finished at veraison in August 2023. Fungicide program efficacy was determined based on disease incidence and severity. Yield was measured by weighing all clusters from each plot. Berry chemistry (total soluble solids, pH, and titratable acidity) was assessed following standard laboratory protocols. Biofungicide active ingredient and mode of action significantly affected program efficacy, while the interval of application did not. All programs integrating biofungicides with synthetics had efficacy comparable to the grower standard which, with the exception of one biofungicide stand-alone program, resulted in significantly higher powdery mildew and Botrytis bunch rot disease control than biofungicide stand-alone programs. Yields were also significantly greater in these programs. This suggested that when designing a program with biofungicides in this AVA, integration with synthetics can significantly improve the efficacy of the programs. Berry chemistry was affected significantly by the fungicide program, but results did not necessarily correlate with their efficacy.

Funding Support: CDFA-Specialty Crop Black Grant Program and CSU ARI