Herbicide resistance across Eastern Canada continues to create management challenges for growers but there are effective strategies to maintain herbicide efficacy and control herbicide-resistant weeds in your fields.

When you look across the spectrum of weed control options, it’s hard to ignore the impact of herbicide resistance. Currently, weed resistance to many modes of action has been confirmed, including the active ingredients in Groups 1, 2, 4, 5, 6, 7, 9, 14 and 22.

But that doesn’t mean herbicides within these groups won’t do a good job of controlling the weeds listed on their labels, says Marijke Vanderlaan, Agronomic Service Representative with Syngenta. “We have lots of glyphosate (Group 9) resistance across Eastern Canada, but that doesn’t mean it can’t give growers effective weed control,” she stresses.

Use multiple modes of action

Vanderlaan says growers can find themselves in a similar situation with a product like atrazine (Group 5). “If you use atrazine on your field year after year, it won’t be long before you have resistant weeds in that field. It really is important for us to protect our crop protection.”

That’s why using multiple modes of action is so important, says Vanderlaan. Currently, there are just two herbicide groups —15 and 3 — with modes of action that have no documented cases of herbicide resistance in Eastern Canada. (There are known cases of Group 27 resistance in both Ontario and Quebec, however these findings had yet to be published as of the date of this posting.)  

“Adding Group 15 and 3 to your herbicide program is the most effective way to delay herbicide resistance in your fields,” Vanderlaan says.

She notes that a product like Acuron^® herbicide combines four active ingredients with three modes of action for control of broadleaf and grass weeds in corn. It contains one Group 15 and two Group 27s, making it a strong choice for resistance management on corn acres.

Fighting resistant waterhemp

Waterhemp is another troublesome herbicide-resistant weed that’s turning up in more fields across Eastern Canada. Glyphosate-resistant waterhemp was first identified in Ontario in 2014. Since that time the weed, which is a member of the pigweed family, has spread across the province and has been confirmed in 13 counties.

To make matters more troubling, waterhemp resistance continues to grow beyond glyphosate, and now includes multiple resistances to Group 2, 5, 9 and 14 herbicides.

“We already have multiple resistance within waterhemp, but we have three effective modes of action — Group 27, 15 and 5 — that work on the weed so we will have effective tools moving forward,” says Vanderlaan. She notes that Boundary^® LQD herbicide, which contains Group 15 and 5 modes of action, offers effective control of resistant waterhemp, which can be especially troublesome in soybeans.

“We have to remember that we do have effective weed control products in our toolbox,” says Vanderlaan. “And when we use them in the right combination, we still have the capability to manage these challenging weeds.

​​​​​​​For more information including articles, resources and videos on resistance management, check out Manage Resistance Now. This is a collaborative effort of industry, academia and government experts, brought together by CropLife Canada, to raise awareness and promote the adoption of strategies to manage weed, insect and disease resistance.