Insecticide field trials were conducted in Ontario, Canada, and New York state to identify insecticides effective against the swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae), a new invasive pest in North America. Field trials indicated that foliar applications of lambda-cyhalothrin, permethrin, acetamiprid, chlorpyrifos, and dimethoate could provide control of C. nasturtii. Foliar insecticide applications were effective in keeping damage within marketable limits in all cabbage and some broccoli trials during the early phase of regional colonization by C. nasturtii (2001-2002). However by 2005-2006, treatments were rarely able to maintain damage levels within marketable limits. Low efficacy suggested the possibility of insecticide resistance in Canadian C. nasturtii populations, but laboratory assays revealed no evidence for resistance. Thus, eventual control failures on a season-long basis were apparently due to very high populations during later phases of colonization in Ontario. Early season applications (e.g., seed treatments, greenhouse plug tray drenches and/or band sprays) of neonicotinoid insecticides proved effective for 3-5 wk after transplanting in New York. These early season treatments would require supplemental control with foliar insecticides, but would reduce the number of foliar applications required and thus reduce insecticide usage. Our results suggest that acceptable control with foliar insecticides will be difficult where C. nasturtii populations are high, because of multiple and overlapping generations, and difficulty in achieving adequate spray coverage. An integrated pest management program that uses cultural control methods and host plant resistance, with judicious use of insecticides, is needed for sustainable management of this newly invasive pest.