Effect of season-long insect injury on sour rot severity in ripening wine grapes

Sour rot is an important grape disease complex that involves the association of microbes and Drosophila vinegar flies. Grapes are attacked by various other insect pests throughout the growing season, creating injury and opening pathways for microbes. There is limited knowledge about how season-long insect damage affects sour rot severity at harvest. We studied how pest infestation timing influences sour rot development and the reproductive output of Drosophila in rot-susceptible vineyards. To compare damage timings, clusters were exposed to mechanical damage or not and with or without D. melanogaster at different timings between bloom and harvest. In a second experiment, grape clusters were enclosed in mesh bags and subsequently exposed to pest infestation at different times by removing exclusion bags monthly from June to September. Clusters were rated for the incidence and severity of sour rot at harvest time in both trials, and Drosophila flies were reared from those clusters. This study will help our understanding of how season-long insect injury influences sour rot and will inform development of precise and timely management strategies.