Fighting herbicide resistant weeds with change

Multiple modes of action and stacked seed traits help farmers manage resistance

When it comes to herbicide resistance, chemical companies are focusing on multiple modes of action. More varieties with stacked herbicide-tolerant traits are also on the horizon. But as western Canadian farmers sail towards that new future, they should keep in mind management goes hand-in-hand with technology.

Stacked herbicide-tolerant traits are a new tool, giving farmers an easier way to use multiple modes of action, said Joe Vink, weed management technical lead with Monsanto Canada. “But by no means are they a silver bullet for preventing herbicide resistance.”

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Seeding near the Goyder Line, Peterborough, South Australia.


Monsanto’s Roundup Ready 2 Xtend soybeans will tolerate both glyphosate and dicamba. “When you have Roundup and dicamba, you have two effective modes of action on emerged broadleaf weeds,” said Vink. “But then you also have that added residual from the dicamba portion, which is an added benefit.”

Monsanto has other stacked herbicide-resistant traits that are further out, said Vink. Future generations will be tolerant to several modes of action, he adds. The company plans to launch Roundup Ready 2 Xtend in Canada by 2016, if global regulatory approvals come through.

Asked how farmers will control volunteers with stacked tolerance traits, Vink said the herbicides available today will control volunteers. “There just needs to be some thought around the rotation and the herbicide programs.”

Stacks in canola are also coming, said Vink, although they’re a little further out than soybeans.

Monsanto isn’t the only company sliding multiple herbicide resistance traits into new varieties. Dow AgroSciences’ Enlist corn and soybeans include glyphosate and 2,4-D-resistant traits. Enlist varieties are part of the company’s focus for Eastern Canada, said Brian Wintonyk, western crops agronomist with Dow. Stacked traits will be introduced to Western Canada at some point, said Wintonyk.

Multiple modes of action

For the western Canadian market, Dow is examining existing chemical groups, as there can be significant differences within a chemical family, said Wintonyk. He’s seen fields where weeds are resistant to one Group 2 mode of action while another Group 2 is still effective.

Wintonyk said that if industry is mindful and plans rotations, “we can extend the life of some of the products that may not seem like they have much life left.”

Wintonyk said they’re also looking at modes of action that aren’t used as frequently these days. For example, Edge is a Group 3 that works for Group 2 and 9 resistant kochia. “The risk for selecting resistance there is low compared to Group 2s,” he said.

BASF’s focus over the next two or three years is getting additional modes of action in the tank with glyphosate, said Danielle Eastman, brand manager for western herbicides and Clearfield.

Eastman said the company is asking growers to add “an additional, unique mode of action, be it a Group 14 that’s in our Heat LQ herbicide or another group, in order to manage those Group 2 and those glyphosate-resistant weeds.”

All three company reps agreed that farmers should use two modes of action that are active on the weeds they’re trying to control.

“If you apply a broadleaf herbicide with a grass herbicide, well then you still only have one mode of action on broadleaves and one mode of action on a grass,” said Vink.

The same principle applies when controlling herbicide-resistant weeds. For example, Eastman said tank-mixing a Group 2 herbicide with glyphosate for a pre-seeding application in cereals isn’t “necessarily the best practice since a lot of those weeds are already resistant to Group 2 herbicides. So you’re really only relying on the glyphosate to get control of that weed, specifically.”

Western Canadian farmers are managing herbicide resistance better than other world areas, said Vink, partly because they have “pretty solid crop rotations.”

Along with rotating crops and herbicide groups, and using multiple modes-of-action, company reps are encouraging farmers to adopt other management practices.

Dow encourages practices such as equipment hygiene to control weeds, said Wintonyk. He also advocates changing farming practices to throw weeds off balance.

For example, while it makes sense to seed whichever field dries out first each spring, that means the same field probably gets seeded first each spring, Wintonyk said. Seeding that field a couple of weeks later than usual throws weeds off their game.

Glyphosate resistance has perhaps had one silver lining. Because of the attention around the problem, said Vink, “people are making management changes and I think it really does make a difference, long-term.”

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.

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