P-648 - A strategy to control brown rot blossom blight of peach and lower pesticide risk

Monilinia fructicola is a major pathogen of stone fruits worldwide and causes blossom blight and brown rot in peach and nectarine. Blossom blight infections lead to spore production on decayed flowers and associated cankers. These spores serve as inoculum for green fruit rot and brown rot. In 2024 and 2025, field trials were conducted at Clemson University’s Musser Fruit Research Center in Seneca, SC to evaluate conventional and biorational fungicide spray programs for managing blossom blight on 10-year-old ‘Juneprincess’ nectarines. A randomized complete block design with four trees per treatment was used, and fungicides were applied during bloom. Blossom blight incidence was assessed on 30 twigs per tree, and data were analyzed via ANOVA (P < 0.05) followed by Tukey´s test. In untreated controls, blossom-blight incidence on twigs was 68.3% in 2024 and 45.0% in 2025. The biorational fungicide Howler EVO (Pseudomonas chlororaphis AFS009) did not significantly reduce disease in either year. However, Theia (Bacillus subtilis AFS032321) significantly reduced blossom blight incidence in both years and even performed as well as the chemical standard Propi-Star (propiconazole) in 2025. A combination of Howler EVO and a half label rate of Propi-Star effectively reduced blossom blight in both years, matching the efficacy of the full label rate of Propi-Star. The results suggest that biorational fungicides, particularly in combination with reduced rates of propiconazole, hold promise for sustainable blossom blight management in nectarines.