The Agronomists, Ep 65: Rob Bahry and Marc Maisonneuve on managing herbicide resistance


Biology is forever adapting — to tillage, to cropping systems, and to selection pressure of herbicide applications.

The advent of herbicide resistance has created a huge challenge for farmers across North America. Some of the worst weeds include kochia, fleabane, wild oats, waterhemp, and Palmer amaranth.

Managing these weeds and delaying more resistance requires a thorough plan, and to help build the plan, we go to Rob Bahry of ADAMA Canada and Marc Maisonneuve of Corteva Agriscience, on this episode of The Agronomists.

Catch a new episode of The Agronomists every Monday night at 8 pm E!



  • Integrated approach. There are many factors that impact herbicide performance
  • There is 19 different herbicide groups listed in Manitoba. Let’s not use the same mode of action over and over.
  • Kochia is a focus in the west, because of how it is so resistant
  • How do weeds become resistant? Overuse, lack of changing what we are using, lack of crop rotation, plus the weeds themselves
  • Two types of resistance: metabolic resistance and target site resistance
  • There are lower risk of resistance products, but all products are at risk for resistance to some level
  • Why are some weeds more prominent to resistance than others?
  • It doesn’t have to be consecutive applications to start developing resistance
  • Let’s say it a little louder for the ones in the back: tank mix!
  • The problem can just get worse and worse and worse…plan ahead, if you can
  • It’s a numbers game. Depends on how many seeds the weed happens to have can speed up the process

CLIP 1: Pulse School: Herbicide Layering — The Tag Team Approach to Fighting Weeds and Resistance

  • No-till and chem fallow — has this accelerated herbicide resistance? In short — yes. Especially when it comes to glyphosate
  • Is there still a time and place for just glyphosate alone? If we can help it…no
  • When we adapt our strategies, the plants just adapt as well
  • Herbicide layering. If you haven’t looked into it, you should

CLIP 2: Cleaning up the “waste areas,” with Dale Cowan

  • Understanding the weeds you are up against and how the seeds spread is key, too
  • Goats or sheep will eat these weeds! Ruminants for the win? (Depends who you are talking to)
  • Weeds will always find a way…
  • Mowing and managing a weeds spread can be helpful, too
  • You have to catch these weeds before they go to seed
  • To detect herbicide resistance, the first step is to of course scout
  • Rotating buys you time; mixing buys you shots
  • The management piece is really important when it comes to weed control. Integrated pest management
  • We can’t spray our way out of resistance
  • If we are to take glyphosate out of the mix entirely, it complicates things in a big way
  • Glyphosate takes the place of tillage in a lot of places…by removing glyphosate, it could bring back more tillage

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Other Episodes

The Agronomists (view all)Season 3 (2022) Episode 31

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