It’s not always the neighbours with resistant weeds

It was an unscientific poll of farmers on a webinar, but it was telling nevertheless.

About 53 percent of respondents said they have herbicide-resistant weeds on their farm. And 82 percent said their neighbours do.

Charles Geddes, Agriculture Canada research scientist in weed ecology, was not surprised by those contradictory results. They do show, however, that awareness of herbicide-resistant weeds is growing, at home and next door, along with the prevalence of the weeds themselves.

The three prairie provinces now have an estimated 23.7 million acres infested with herbicide-resistant weeds, which cost them about $528 million annually. Alberta has 26 unique resistant biotypes, Saskatchewan has 21 and Manitoba has 23.

Globally, Canada is in third place in number of herbicide-resistant weeds, behind the United States and Australia.

In the webinar organized by Alberta wheat and barley organizations, Geddes said about 60 percent of Alberta fields surveyed have some resistant weeds, according to surveys. In Saskatchewan, 57 percent are hosts to such weeds and in Manitoba it’s 68 percent.

“When we’re talking about these different types of herbicide resistance, there is an issue because we’re working with a limited number of herbicide modes of action,” said Geddes. “There really has not been a new mode of action released in the last three decades, up until just recently, where there was a mode of action released for production systems that are outside of what we would use here in Western Canada.”

In Alberta, about 58 percent of surveyed fields have Group 1 resistant wild oats (in Saskatchewan its 59 percent and in Manitoba 78 percent) and about 40 percent have Group 2 resistant wild oats (Saskatchewan 32 percent, Manitoba 43 percent). Some resistance to Group 8 herbicides has also appeared, although more surveys are needed to gauge levels.

Most of the remaining options for wild oat control are designed for pre-emergence, Geddes said, so in-crop options are becoming limited.

“One of the big gaps that needs to be addressed in weed science, especially in Western Canada here, is looking at some of these other pre-plant herbicides. You’ll see all of the herbicides labelled as suppression now and (research is needed to see) if there is a way that we can increase the control that we’ll receive in terms of those pre-plant residual herbicides to help with wild oat management once we’re dealing with multiple resistance in wild oat.”

Geddes also has data on Group 3 and Group 1 resistant green foxtail and Group 2 resistant green foxtail, chickweed, cleavers, lamb’s quarters, narrow-leaved hawk’s beard, shepherd’s purse, smartweed, spiny annual sow thistle and stinkweed.

Kochia is a big focus in Alberta, where resistance to Group 2 herbicides was noted in the late 1980s. It developed to the point where all kochia in Western Canada is considered to be resistant to all ALS inhibitors.

Glyphosate resistant kochia was first identified in 2011, when about five percent of the kochia population was considered to be resistant. Within the next five years that rose to 50 percent.

“In addition to glyphosate resistance … they also found dicamba resistance, or synthetic auxin resistance, for the first time in kochia in Alberta,” said Geddes. “So we have triple resistant kochia in about 10 percent of those populations.

“What this indicates is that I suspect these are actually separate modes of action that are conferring resistance to each of those herbicides but also it shows that in that survey we underestimated the synthetic auxin resistance that we have here in Alberta.”

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