Date of Award


Degree Name

MS in Agriculture - Plant Protection Science


Horticulture and Crop Science


College of Agriculture, Food, and Environmental Sciences


Shunping Ding

Advisor Department

Horticulture and Crop Science

Advisor College

College of Agriculture, Food, and Environmental Sciences


Botrytis bunch rot (BBR), caused by Botrytis cinerea, leads to a severe reduction of quality and yield in wine grapes (Vitis vinifera). A field study to determine the best BBR management strategy was conducted in 2021 and 2022 in Santa Maria, CA using ‘Chardonnay’, a BBR susceptible wine grape cultivar. Three biofungicides were evaluated: Actinovate® AG, Regalia®, and Serenade® ASO. The efficacy of these three biofungicides was compared with fungicide programs composed of commonly used synthetic fungicide(s) or combinations of commonly used synthetic and biofungicides. For each biofungicide, three application timings were evaluated: 7-day interval, 14-day interval, and by an incubation predictive model. At 21- and 7-days pre-harvest (2021 and 2022), 25 clusters per treatment replication were evaluated for BBR incidence and severity to determine the efficacy of each treatment. All biofungicides and control treatments resulted in significantly lower disease severity and incidence compared to the untreated control. Treatment programs were comparable in both years, except in 2021, BBR severity was observed to be significantly lower (P < 0.001) when treated with the rotation of synthetic fungicides and Actinovate sprayed weekly compared to Actinovate sprayed based on the predictive model. The relation between airborne conidia counts, environmental conditions, and disease severity were investigated. Correlations between environmental conditions and airborne conidia counts were not found in 2021. However, in 2022, the number of airborne conidia were observed to be positively correlated with minimum temperature (P = 0.016) and negatively correlated with wind speed (P < 0.001) v in the studied vineyard in Santa Maria. Meanwhile, the number of airborne conidia were observed to be positively correlated with average temperature (P = 0.042) in the vineyard in San Luis Obispo. No correlations were found between disease severity on grape tissue and the number of conidia trapped regardless of year and location. Biofungicides evaluated in this study have the potential to be used for BBR management in ‘Chardonnay’ grapes, but further investigations may be needed to confirm these findings.