Current IPM Practices for Managing Late-season Swede Midge (Contarinia nasturtii) in Minnesota

September 15, 2017

W. D. Hutchison1 and Angie Ambourn2
1Extension Entomologist, Department of Entomology, University of Minnesota, St. Paul, MN
2Plant Protection Division, Minnesota Department of Agriculture, St. Paul, MN

Life-cycle, Biology & Damage:  With infestations documented in 2016 and 2017 in the Twin Cities metro area, it is likely that SM may be able to overwinter in MN (at least southern MN), but the pest may also enter the state on transplants.  Research is needed to better understand the ability of the pest to overwinter in the state, as well as its life cycle under MN conditions.  Background information on the identification, life cycle, host range and damage caused by this new, invasive pest in MN are available: 
UMN VegEdge, SM pest profile: https://www.vegedge.umn.edu/pest-profiles/pests/swedemidgepp  
Cornell University:  http://web.entomology.cornell.edu/shelton/swede-midge/management.html

Host Range – Multiple Crucifer (Brassica) Crops & Weeds in the Mustard Family:  Nearly all crops in the mustard family (Brassica’s: broccoli, brussels sprouts, cabbage, cauliflower, mustard greens, kale, canola) as well as several weed species (wild radish, Shepherd’s purse, field pennycress) can serve as hosts for Swede midge. In addition to managing the pest in specific crops, growers should also control all mustard weed hosts within farm fields and in field margins, or fence rows, to reduce SM pressure.  This should be done in the fall as well as during the growing season.

Sanitation and Crop Destruction:  Although we do not have specific data for SM, recent studies with other, similar pests (e.g., a fruit fly, spotted wing drosophila), have shown that placing infested plant material in plastic bags (clear plastic), and exposing the bags to sunlight for 4-5 days, should generate enough heat (e.g., >120 to 140F) inside the bags to kill SM. This may be reasonable for small or community gardens, particularly where SM has recently been detected.  After 5-7 days, the bags can be buried or destroyed.

Composting Options:  Again, without specific research for SM, one can still consider the benefits of composting for SM control. Although this approach may be less effective than bagging plant material, it is likely more feasible for larger growers.  Ideally, SM infested plants should be placed in compost pile (system) that with appropriate aeration/sunlight can reach 120-140F. In Minnesota, if a given county (e.g., Ramsey Co.) maintains a municipal compost site, and the source farm is in the same county, the plant material can be moved to the municipal site for composting.  However, in the case of Hennepin County, where such plant material is often transported to another county, not known to be infested, the municipal site cannot be used.  Perhaps the best option, particularly for an invasive pest, is to compost the material on site, to minimize movement of the pest.

Minimize or Avoid Planting Crucifer (Mustard) Crops in 2018.  Looking ahead, perhaps the most impactful option for community gardens, and if everyone in a given community can agree to follow the recommendation, (and small farms) is to simply avoid planting brassica crops for at least 1 or 2 years, to help “break the life cycle” of the pest, at least at the local level.  For this to be effective, weed hosts would also need to be managed.  Again, more research will be needed to fully understand the timing of spring emergence of SM in Minnesota, and to develop effective management strategies.

Growers who suspect they may have Swede midge infestations, should collect samples, and contact the MN Pest Alert Program, at: email: arrest.the.pest@state.mn.us

swede midge adult