Glyphosate resistant fears become reality

Glyphosate resistant wild oats have been found in Australia, which may not bode well for Canadian growers.

“Glyphosate resistance in wild oat would be a huge issue for agriculture in Western Canada,” said Charles Geddes, a research scientist with Agriculture Canada.

“Most farmers are currently dealing with herbicide resistant wild oat as it is; adding glyphosate resistance on top of that would be very difficult for farms to manage.”

When Hugh Beckie worked at Agriculture Canada as a research scientist, he ran models to see which weeds were likely to develop glyphosate resistance in Western Canada. Wild oats were at the top of the list, followed closely by cleavers.

“We expect that this may be an issue on the Prairies in the future, but to date with all of the testing that we’ve done we have not confirmed any glyphosate resistance wild oat on the Prairies,” Geddes said.

The Group 9 resistant wild oat biotype was identified by Bhagirath Chauhan in the Australian state of New South Wales.

He uploaded information from his study to weedscience.org, which hosts an international survey of herbicide resistant weeds.

Chauhan’s study identified a sterile oat biotype that had developed resistance to Group 9 herbicides, but he also confirmed on Twitter that glyphosate resistant wild oats were also identified on the same field.

Geddes said glyphosate resistant wild oats found in Australia should serve as a warning to growers in Canada.

However, he said because this biotype has not been found on the Prairies, there is still time to use preventive measures to stop it from developing in Canada.

Geddes said glyphosate resistant wild oats would cause big problems in prairie fields, which already have wild oats resistant to groups 1 and 2 herbicides.

Most wild oat populations with group 1 and 2 resistance on the Prairies have blanket resistance to many of the active ingredients within both those modes of action.

“Currently, even without glyphosate resistant wild oat, we’re sitting at a point in small grain cereals where there are no post-emergence options for wild oat management,” Geddes said.

“So that means that once you have that type of resistance, we’re already relying on pre-emergence herbicides for controlling wild oats in small grain cereals, and many of the pulses as well.”

The greatest amount of glyphosate applied on the Prairies is for pre-emergent burn-downs for broad spectrum control.

Growers in areas where there are group 1 and 2 resistant weeds rely on glyphosate for pre-plant weed control.

If glyphosate resistant wild oats do come to prairie fields, part of the efficacy of the pre-plant application of the herbicide will be lost.

This would result in more weeds emerging in-crop and increase reliance on post-emergence herbicides.

“But again, in the case of group 1 and 2 resistant wild oat, we’ve already lost many of those post emergence options,” Geddes said.

The management of cereals and pulses would be greatly affected if glyphosate resistant wild oat develops on the Prairies.

“In addition, it will also have a large impact in any of the glyphosate resistant crops, for example, Roundup Ready canola or Roundup Ready soybeans, where the main post-emergence application relies on glyphosate,” Geddes said.

“I fear that if we do see more and more glyphosate resistant weeds on the Prairies, that will cause more growers to have to revert to tillage for pre-plant weed control, which is something we don’t want from a sustainability perspective.”

He said wild oats are primarily a self-fertilizing species, which means that the rate of outcrossing in the weed is lower than other problematic species such as kochia.

“Usually when we see resistance show up, it’s less due to those resistance genes crossing and transferring from field to field through pollen, for example. It’s more due to selection in that field and survival of those resistant biotypes,” Geddes said.

This means the emergence of a glyphosate resistant biotype will likely occur on a field-by-field basis, and growers can control the selection pressure on their own farms rather than rely on their neighbours’ stewardship.

As a result, there is still time for growers to integrate non-chemical weed control into their cropping systems before glyphosate resistant wild oats develop in their fields.

For example, several studies have shown that increasing seeding rates in cereals is economically viable and can help crops outcompete weeds, including wild oats.

Geddes said Agriculture Canada researcher Breanne Tidemann has done work that shows clipping wild oats above the crop canopy before the seeds become viable can help with bad infestations.

Patch management can also help reduce the development of herbicide resistance in wild oats.

Using multiple effective modes of action for pre-emergence burn-downs will go a long way to slowing the development of glyphosate resistant wild oat, Geddes said.

Agriculture Canada offers free testing of grower submitted samples for weed types that have not been well documented on the Prairies, including glyphosate resistance specifications other than kochia.

“So if a grower suspects they do have glyphosate resistance, I would urge them to contact myself and I can provide them with a form to fill out and we can test it for free,” Geddes said.

The testing is confidential and will not be traced back to individual farms.

About the author

explore

Stories from our other publications