D3422: Swede midge: An emerging invasive pest in urban gardens in Minnesota

Swede midge (Contarinia nasturtii Kieffer) is an invasive fly in the Cecidomyiidae family, found in southern Ontario in 2000 and first detected in Minnesota in 2016. A brassica-family specialist, swede midge targets economically important crops including canola, broccoli, cauliflower, and kale. Females lay eggs in developing plant tissue and larvae can cause significant damage including disruption of head formation and head rot, multiple shoot growth, leaf curl, and scarring. Since initial detection, swede midge has become established in urban and community gardens in Minnesota and is limiting production and quality of brassicas at these sites. In some locations, swede midge damage has led to implementing bans on planting brassicas, showing that there is a need to develop appropriate management strategies for this pest in urban gardens. Using pheromone baited traps, we sampled swede midge adult populations at five urban garden locations in St. Paul for the entire growing season (mid-May to mid-October) in 2022, 2023, and 2024. In 2023, we established experiments at three urban community garden sites using row covers to prevent infestation in plants, in conjunction with weed barriers to prevent new generations of swede midge adults from emerging from the soil. Initial results show this is an effective management strategy, and gardeners are testing the method in 2024. A survey of urban gardeners at the end of the 2023 season, with 28 respondents, showed that physical exclusion, crop selection, and botanical-based repellents were the most attractive management strategies to explore for this invasive pest in urban settings.