Producers urged to limit glyphosate

Chem-fallow fields an issue | Growers advised to stop using glyphosate as standalone herbicide

An Agriculture Canada weed scientist is praising farmers two years after a new herbicide resistant weed was discovered in Western Canada.

However, while Hugh Beckie said many growers are taking the necessary steps to delay the spread of herbicide resistant weeds, some may want to rethink how they employ chem-fallow fields in their cropping systems.

Beckie, who updated growers on the spread of glyphosate resistant kochia Jan.14 during CropSphere in Saskatoon, recommended tank mix herbicides to help farmers manage the weed.

“We’re seeing a trend of growers tank mixing their glyphosate with another herbicide mode of action,” Beckie said following his presentation.

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“Industry gets a lot of credit for providing incentives to do that.”

Agriculture Canada officials confirmed the first cases of glyphosate resistant kochia in Alberta’s Warner County in 2011.

Since then, surveys and testing have identified more populations of the resistant tumbleweed: in Sask-atchewan, further north and in the province’s southwestern corner, and one case in Manitoba.

Surveys for 2013 aren’t complete, but Beckie expected them to reveal a greater spread of the weed.

Chem-fallow fields, which receive multiple applications of glyphosate over a growing season, are in most cases ground zero for resistance. Fields appear barren except for long strips of kochia.

“A few years ago farmers were tank mixing glyphosate in the burn-down treatment to control the early emerging weeds, and then when the price of glyphosate dropped, we got into a bad habit of just using gly-phosate alone at very high rates,” Beckie said.

He presented sales figures from 2012 that showed glyphosate making up more than half of all herbicide purchases.

He urged growers to avoid using glyphosate as a standalone herbicide whenever possible.

“We’re not going to find another glyphosate in the future and there’s not going to be any silver bullet when it comes to weed management in the future because the rate of herbicide discovery has just dropped off to almost zero,” said Beckie.

Officials are quick to point to the southern United States, where the frequent cropping of Roundup Ready cotton has led to the widespread presence of glyphosate-resistant Palmer amaranth, which has had a dramatic effect on production to the point where farmers are forced to pull weeds by hand.

“Kochia is sort of our Palmer amaranth in the north,” said Beckie.

“There is still a number of options to control it, to manage it, and I think growers are doing the best they can to keep it under control and not to impact yields and quality too much.”

Managing glyphosate resistant weeds may require tillage or additional herbicides, which increases costs.

Options are available for tank mixes that use Group 4 and 14 modes of action for chem-fallow, canola, wheat and barley.

However, repeated use of those chemicals could lead to multiple levels of resistant. It’s already seen in kochia that is resistant to Group 2 and 9 herbicides.

“We are running a risk, then if we keep chem-fallowing frequently,” said Eric Johnson of Agriculture Canada, who estimated chem-fallow acres in Western Canada at six million.

“I’m afraid we’re going to end up with three or four resistances. I think we have to re-evaluate chem-fallow. If you don’t think that’s possible, go to Australia. There are biotypes there with seven modes of action that they are resistant to.”

Johnson cautioned against tank mixing with 2,4-D.

“Tank mixing with 2,4-D is not an option in chem fallow or in pre seed burn off,” he said.

“You have to use something much stronger than that.”

Crop rotations are important to delaying resistance, said officials.

Beckie said the two-year canola rotation that is common in Western Canada is unsustainable for weed and disease management, but the region’s overall crop diversity is positive.

However, the introduction of corn and soybeans in Western Canada could alter the dynamics.

“We don’t want to get into a Roundup Ready corn-Roundup Ready soybean rotation that’s common in the Midwest U.S.,” said Beckie.

“That really creates tremendous selection process for glyphosate resistance.”