Residual Control on Swede Midge

Swede midge is relatively new to Ontario but it already has a reputation as a pest that is very tough to control. It can have four to five overlapping generations over the growing season. That makes it difficult to time an insecticide application so that it is both effective and economically viable.

What is swede midge (Contarinia nasturtii)

  • A pest of crops in the family Brassicaceae, was first identified in Ontario in 2000.
  • The tiny, light-brown adult swede midge is hard to tell apart from other midges and the larvae are even harder to scout. It’s the extremely small larvae that do damage to the crop.
  • According to an Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) fact sheet about swede midge, the larvae are initially 0.3 mm long and transparent and typically feed in groups near the growing point.

Integrated pest management is key

Damage from swede midge can be confused with other common problems in crucifer crops. When swede midge first showed up in Ontario, growers did not immediately recognize new infestations on the farm. Because of the insect’s biology and reproductive potential, low levels of damage can rapidly become a large problem if the population is left unmanaged. Without a good IPM program that involves regular monitoring, growers can lose the entire crop to swede midge.

Timing of spray

Timing of the insecticide spray is also critical. By the time a grower sees crop damage it’s too late. OMAFRA recommends using commercially available pheromone lures and white Jackson-style traps to track the emergence and activity patterns of the pest to help determine the need and timing of insecticide sprays.

Monitor often

“Growers must follow OMAFRA guidelines and monitor each field and spray early,” says Alam. “Swede midge is not like other pests, such as cabbage looper or diamondback moth, where if you miss spraying one instar you can get them when they’re bigger. In this case, it’s very difficult to see the pest and by the time you see damage, it’s too late.”

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