Sprayed for Swede Midge? Now What?

Question: Once canola starts to bolt, do I need to be concerned about damage from Swede Midge.

Answer: Yes. Canola is susceptible to significant damage up to secondary branch development. Once secondary branches begin to bud, canola is not subject to serious damage. The importance of secondary branches to yield depends on plant density. Under normal plant populations, canola will develop 3-5 secondary branches but under low populations (3-5 plants/ft2) canola can produce many more branches that are important contributors to yield. Many canola stands have lower populations this year. At this time, we just don’t have a lot of answers on the impact swede midge can have on overall yield when canola is affected at various stages. If canola stand is thin or very uneven in growth, longer protection may be required.

Question: I sprayed 7-10 days ago. Will I need to spray again?

Answer: If midge catches in your area remain high (above suggested threshold 25 midge/trap/day) and your canola is still at vulnerable stage (before flowering) then a second application may be warranted. Research conducted by University of Guelph demonstrated that Matador provided 7-10 days control. Coragen is expected to provide similar length of control. Matador provides ‘knock-down’ control of midge adults but re-infestation by midge migrating into a field will need control if high numbers are present. Coragen is most active on the egg and larval stages but does not protect new growth that develops subsequent to application.  We are just not certain the period of control these products will provide. Remember both Matador and Coragen require good coverage, so if foliage is dense increased water volume and selection of correct nozzle is paramount.

 Question: Which product should I use for a second application?

Answer: Coragen and Matador belong to different chemical families and should be rotated for resistance management. A maximum of 3 applications of Matador are permitted per season. If you used a pyrethroid (Matador, Silencer, Ripcord, Decis) to control flea beetles than switching to Coragen would be good choice. It also gives you the option to use a pyrethroid for seedpod weevil should this be necessary at early flower stage of canola. 

Question: I am beginning to see some damage, should I spray.

Answer: Ensure what you are seeing is swede midge damage. Expect to see a little damage. Mechanical damage, hormone herbicide injury can appear similar. The first generation of midge emerged in May, and a low level of plant damage will occur, especially in field margins where overwintering midge migrate in from nearby fields that grew canola in the past. If your canola is at vulnerable stage and trap catches are high in your area, protection will be warranted. When swede midge populations are very high, insecticide sprays alone will not eliminate economic damage. So waiting to see damage will not work, as populations may already be out of control. 

Question: What effect will all this rain and high temperatures have?

Answer: Midge need moisture to develop through their life stages which will be accelerated by warmer temperatures. There can be 4-5 generations of midge per year. 

Question: Once my canola is flowering do I still need to be concerned about midge?

Answer: No, once your crop is flowering including side branches, we believe midge will cause minimal economic damage to your crop. Midge adults lay their eggs in growing point, where larvae  mine into tissue causing damage. At flowering, canola has completed most of its growth and damage will be minor. Please remember to minimize spraying an insecticide during flowering and if necessary apply when bees are not foraging, apply only at dusk or dawn and notify local beekeepers in your area.

 Question: How can I reduce potential for damage in future?

Answer: Tillage of residue shortly after harvest and control of volunteer canola this fall can help reduce overwintering populations. If you had high populations of midge in your area, not planting canola near a field(1500-3000 ft.) that had canola this year can help.