VIDEO: Layers of herbicides help avoid resistance

Layering may be used to reduce multiple resistance in one weed or address several weeds that are prone to resistance

REGINA — Prairie grain producers have been relatively lucky when it comes to herbicide resistant weeds, especially when comparing their experience to some European and American farmers.

However, producers should quickly adopt strategies that reduce the probability of resistance developing in weeds if they want to avoid the staggering costs associated with herbicide resistance, said Clark Brenzil, provincial weed control specialist with Saskatchewan Agriculture.

Brenzil told the Grain Expo held during Canadian Western Agribition that annually rotating herbicide groups has been a common method to combat herbicide resistance on prairie fields.

However, he said it does not stop the development of herbicide resistance.

“We’re finding more and more it delays resistance but doesn’t really reduce the odds of getting it. Weed seed dormancy is the issue,” Brenzil said.

Tank mixing different groups is better than merely rotating herbicide groups because it reduces the risk of herbicide resistance developing.

Another strategy is called layering, which Brenzil said significantly reduces the chance that herbicide resistance will develop.

It uses multiple active ingredients and herbicide groups to control the same weed in the same field in the same year, but the active ingredients do not have to be delivered in the same tank load.

“So what we’re doing is taking one group and we’re putting that as a pre-seed application, then we’re maybe taking another group and applying that as foliar application in crop, and maybe we add another group into the tank with that foliar application,” he said.

“So now we’re getting a buildup of different groups in that same field in the same year.”

This buildup makes it difficult for weeds to develop resistance to any one chemical group because other chemical groups are on hand to take out stragglers.

Layering may be used to reduce multiple resistance in one weed or address several weeds that are prone to resistance to different groups.

Brenzil said producers might see an immediate gain on their return on investment because their crops will have fewer weeds.

“You’ve got multiple active ingredients working all in conjunction with one another and you’re getting that benefit of forestalling resistance, but you’re also getting some added benefits in terms of yield improvements, better weed control in general and lower dockage,” he said.

Herbicide resistance is becoming a problem in prairie fields. Group 2 resistant wild mustard is common in lentil growing regions in western Canada, and there is also Group 2 resistance in stinkweed, wild buckwheat, annual sow thistle, shepherd’s purse, cleavers and hemp nettle. Group 1 resistance is emerging in Persian darnel and kochia has, in some cases, grown resistant to glyphosate.

Brenzil said several weeds are at risk of developing resistance to glyphosate in Saskatchewan

“Anytime you increase the frequency of use of a herbicide, you increase the risk of resistance developing.”

The most important strategy in managing resistance is maintaining diversity, he said. Any system that is not diverse is at higher risk of developing resistance.

“So when we start tightening canola rotations, we need to make sure we diversify our herbicide systems within that.”

Farmers who want to evaluate their specific risk of developing herbicide resistance can visit


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