Efficacy and Economic Viability of Organic Control Methods for Spotted-wing Drosophila in Day-neutral Strawberry Production in the Upper Midwest

Day-neutral strawberry (DNS) production is increasing in the Upper Midwest because of its extended harvest season and greater yield over June-bearing cultivars. However, the longer season increases fruit exposure to the invasive spotted-wing drosophila (Drosophila suzukii; SWD), which threatens the production of small fruits and berries, particularly in organic systems. Numerous pest management tactics have been developed for SWD in recent years; however, relatively few studies have investigated the impact of SWD on DNS. Organic DNS growers need information regarding which management strategy is most effective when compared directly. To address this knowledge gap, we established a 2-year controlled field experiment with organic DNS. We applied treatments that correspond with techniques that local growers reported using or that have shown promise for organic raspberries, including increased harvest frequency, botanical-based repellents, and weekly rotations of organic insecticides, which we compared with an untreated control. We hypothesized that noninsecticidal SWD management strategies would result in fewer SWD eggs per berry and a lower proportion of infested berries compared with those associated with an untreated control. We also hypothesized that noninsecticidal management strategies would be as effective and cost less than organic insecticide applications. We collected data regarding labor hours, direct costs, strawberry yield, and SWD infestation in experimental plots on certified organic land in Minnesota in 2022 and 2023. An average of 33% of strawberries contained SWD eggs. The experimental treatments showed inconsistent effectiveness for reducing infestation compared with that of the untreated control plots and had no effect on marketable plant yield over the 2-year period. Thus, the added labor expense of these pest control treatments yielded net returns that were 17% to 21% below the control. Labor-saving alternatives like exclusion netting or postharvest cold treatments, which reduce fruit pest exposure and egg viability without harming nontarget insects, may offer more cost-effective solutions for managing SWD in organic DNS.