In the northeastern US, swede midge (Contarinia nasturtii Kieffer) has been an especially troublesome pest for organic and small-scale broccoli producers, many of whom do not have the acreage necessary for the primary management strategy of far (3000 feet) and long (3 year) crop rotations. NEW Crop Rotation Recommendations for Swede Midge, a fact sheet based on research conducted by Cornell Vegetable Extension Specialist and Eastern Broccoli trial leader Christy Hoepting, offers new guidelines for managing the midge on smaller farms.

An understanding of the swede midge life cycle informed Hoepting’s work. Overwintering swede midges can spend up to two winters in larval cocoons in the soil. Adults emerge in spring and early summer in fields that were infested during one or both of the previous two seasons. They live only a few days and are weak fliers. If broccoli or another Brassica is present at the emergence site, female midges will deposit eggs, and the population will increase, with the potential for 4 to 5 generations per season. If no Brassicas are growing nearby to support the next generation, the local population will mostly die off within a few weeks.

Working with several growers in Upstate New York, Hoepting monitored swede midge populations and damage throughout the growing season on each farm. She found that a rotation distance of 500 feet was enough to prevent emerging swede midges from finding the new field, as long as that new field was secluded and separated from previously infested sites by a substantial physical barrier (one that midges can’t easily traverse: woodlots are good, but hedgerows and fences are easily crossed). Likewise, a break of 2.5 to 3 months between Brassica plantings – or delaying the first planting until after mid-July to allow time for spring emergence to subside – disrupted the swede midge life cycle and caused midge numbers to plummet, because they had no place to lay eggs in absence of a host crop.

The success of these strategies depends on a few other key practices that are outlined in the publication. See the fact sheet for further information before implementing the new approach. It can be accessed at the link above, or at https://ecommons.cornell.edu/handle/1813/70145.