Reducing cluster rots in Michigan wine grapes using combined pathogen and vinegar fly control

Abstract

Cluster rots pose a significant threat to the wine grape industry, leading to substantial economic losses. This study aimed to determine the performance of multiple treatments targeting cluster rot pathogens and their insect vectors over three years in southwest Michigan. Grape clusters were rated for disease incidence and severity, insects were collected and identified, and pesticide residues were measured on harvested clusters. In 2020, disease incidence decreased significantly when BLAD was applied in combination with the insecticides spinetoram, imidacloprid with beta-cyfluthrin, or zeta-cypermethrin. Similarly, in 2021, clusters treated with cyprodinil plus fludioxonil mixed with insecticides cyclaniliprole, spinosad, zeta-cypermethrin, or imidacloprid plus beta-cyfluthrin significantly reduced disease incidence compared to fungicide alone. Notably, in 2022, treating clusters solely with an insecticide significantly lowered disease incidence compared to treating with only a fungicide. Disease incidence and severity were positively correlated with the number of Drosophila larvae or the adults emerging from clusters collected in the trial. The relationship between disease and insect incidence were significant in 2021 and 2022, highlighting the importance of controlling insect vectors to manage rots. Through chemical residue testing, we identified pesticide programs that resulted in lower pesticide residues on the grapes. Programs that incorporate organic insecticides or sterilants had statistically lower residues than programs with conventional products. Our findings highlight the effectiveness of incorporating insecticides into late-season IPM programs for reducing cluster rots in wine grapes as managing insect vectors mitigate the impact of cluster rots on grape production.