How effective is a crop sanitizer against yeasts associated with spotted-wing drosophila (Drosophila suzukii) and fruit rot fungi?

Spotted-wing drosophila, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is an invasive vinegar fly which poses a threat to small fruit production, because females lay their eggs in ripening fruit, damaging otherwise marketable product and causing significant financial losses. In addition, egg laying and larval feeding likely increase the risk of fruit rot infection. Current management strategies rely on frequent applications of broad spectrum insecticides to control adult D. suzukii, which is not economically or environmentally sustainable. The use of crop sanitizers containing peroxyacetic acid and hydrogen peroxide (PAA-HP) have shown potential to reduce D. suzukii infestation in blueberries. It is hypothesized that PAA-HP controls yeasts, which decreases favorability of fruit for D. suzukii and fruit rot fungi. In this laboratory study, detached blackberry fruit were inoculated with D. suzukii-associated yeasts and fruit rot fungi then dipped in either 1% PAA-HP solution or sterile water. PAA-HP treated blackberries contained on average 85.7 ± 3% fewer colony forming units (CFU) and 88 ± 6% fewer fruit rot fungal CFU than the control treatment. In addition, in agar plug diffusion assays PAA-HP inhibited fruit rot fungal growth in a dose-dependent manner. Inhibition varied with time of application, between fungal species, and between isolates of the same species. These results indicate that PAA-HP could reduce but not eliminate D. suzukii-associated microbes and fruit rot pathogen infections. Further study is required to determine how quickly microbe and fruit rot pathogen populations rebound after PAA-HP treatment to provide insight into field efficacy.