Simulated crop rotation systems control swede midge, Contarinia nasturtii

Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae), a common insect pest in Europe and a new invasive pest in North America, causes severe damage to cruciferous crops. Many counties in Canada and the USA, in which C. nasturtii has not been previously reported, are at risk of being infested by C. nasturtii. Effectiveness of chemical control is limited, especially under high population pressure in fields. Alternative management strategies against C. nasturtii are sorely needed in order to protect crucifers. Under controlled laboratory conditions, the effectiveness on C. nasturtii control by 11 simulated cauliflower-sweet corn and cauliflower-kidney bean crop rotation systems was evaluated, with and without the presence of cruciferous weeds as alternative hosts. Our results indicated that when soil was infested with C. nasturtii pupae, the emergence pattern from the soil was very similar regardless whether the soil was later planted to host or non-host plants. As emergence was not affected, we examined whether manipulating host availability for oviposition through crop rotation would be effective. Our results indicated that the simulated cauliflower-sweet corn and cauliflower-kidney bean rotation systems provided full control of C. nasturtii. The effectiveness of one cycle of non-host crop rotation was reduced when cruciferous weeds were present. However, the C. nasturtii population in a one-cycle non-host rotation system with cruciferous weeds present was significantly lower than that in a non-rotation system. Two consecutive cycles (simulating a cropping season) of non-host plant crop rotations provided full control of C. nasturtii, regardless of the presence of the cruciferous weeds. The importance of cruciferous weed management and how to implement a successful crop rotation in fields to control C. nasturtii are discussed.