Don’t sacrifice beneficial insects to kill the pests

Including insecticide with herbicides may seem like a proactive, time-saving measure — but the practice can cause more harm than good.

“Using insecticide ‘just because’ kills insects that reduce pest insects. Spray insecticide only when absolutely necessary,” Scott Meers, Alberta Agriculture and Rural Development’s entomologist at Brooks, wrote during the most recent weekly bug chat on Twitter.

Cereal leaf beetles, which are established in southern Alberta and around Edmonton, very rarely reach economic thresholds and minimal spraying has been done, Meers wrote.

“Tetrastichus julius is a very effective parasitoid if we spray only when absolutely needed,” Meers wrote. The wasp, which is about two or three millimetres long, lays five to six eggs in each cereal leaf beetle larva. Each growing season sees two wasp generations.

Some flies also parasitize pest insects, such as cutworms. Insects such as ground beetles, spiders, and daddy long legs also feed on a range of pests. Unnecessary or ill-timed spraying can also harm pollinators such as honey bees.

Here are tips for protecting beneficial insects, from Saskatchewan Agriculture’s AgriView newsletter:

  • Keep in mind that flowering crops and weeds attract beneficial pollinators.
  • Use economic thresholds.
  • Check the 2013 Guide to Crop Protection for residue hazard ratings. Use least the least toxic option.
  • Minimize drift. Only spray when there’s little wind.
  • Spray insecticides after 8 p.m. and before dusk. Bees don’t forage at this time.
  • Many seeds, such as corn and canola, are coated with systemic insecticides that affect non-pests. Follow best management practices during seeding.

The next Alberta bug chat is slated for Wednesday (June 12) at 10 a.m. MDT. Tune in by following #ABbugchat on Twitter, or entering #ABbugchat at

— Lisa Guenther is a field editor for Grainews at Livelong, Sask. Follow her @LtoG on Twitter.

About the author


Lisa Guenther

Lisa Guenther is the editor of Canadian Cattlemen. You can follow her on Twitter @LtoG.


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