More than half of fields surveyed had a resistant weed, with Group 1-resistant wild oat at the top of the list
Alberta’s herbicide-resistant weed survey is underway this summer, but the results from Saskatchewan paint a grim picture of what to expect here.
“Since 2009, there’s been an 89 per cent increase in the land area affected by herbicide-resistant weeds,” said federal research scientist Breanne Tidemann.
“We are in a fairly steep incline in terms of herbicide resistance in the Prairies.”
While Alberta’s survey results won’t be available until next year, Saskatchewan researchers have surveyed 400 fields across the province to evaluate Group 1 and Group 2 herbicide resistance.
“Out of those 400 fields that were randomly selected, 57 per cent of them had a herbicide-resistant weed. Over half of the fields they looked at had a herbicide-resistant weed,” said Tidemann.
“If you extrapolate that to the actual number of fields in Saskatchewan, that’s over 60 per cent of fields.
“We expect to be quite similar to Saskatchewan.”
Wild oat remains the No. 1 resistant weed, she added. “Of the fields surveyed, 49 per cent of them had a herbicide-resistant wild oat. Basically one in two that they looked at had a herbicide-resistant wild oat.”
In those fields, 45 per cent had a Group 1-resistant wild oat, 21 per cent had a Group 2-resistant wild oat, and 16 per cent had resistance to both.
“We expect some of those numbers to be similar or higher in Alberta. That’s how they’ve been in the last couple of years,” said Tidemann.
“And in the fields with Group 1 and 2 resistance, there’s a whole lot fewer options available in some of those fields.”
Cleavers a question mark
Despite the increase in Group 1-resistant wild oats, Group 2-resistant cleavers didn’t increase from the last survey in 2009. They were found in about 20 per cent of fields, Tidemann said.
“That really surprised me, and I’d be really surprised if we saw the same thing in Alberta, just because of the sheer number of cleavers that we’re seeing and a lot of them with Group 2 resistance,” said Tidemann, adding that redroot pigweed, shepherd’s purse and stinkweed are three new Group 2-resistant species that were found in Saskatchewan.
“I expect us to be increasing in terms of Group 2 resistance.”
And once producers lose those modes of action to manage weeds, their control options are relatively limited. One option is winter cereals, said Tidemann.
“One of the biggest messages you’ll hear right now in terms of managing weeds — and in particular herbicide-resistant weeds — is that diversity is key,” she said.
“Diversity in your crops, diversity in your rotations, diversity in your weed management tools — it’s all about diversity.
“What winter cereals do is bring diversity into your cropping rotation.”
Winter cereals can outcompete spring annual weeds.
“When you already have an established crop in the spring, those spring annual weeds have a much harder time establishing because they’re already facing more serious competition,” said Tidemann.
“The canopy is less open so it’s harder for them to get light. The root systems of the winter cereals are more established, so it’s harder for them to get nutrients. It’s harder for them to compete with those winter cereals.”
In Australia, harvest weed seed management is another tool gaining traction, and it too works best with winter cereals. For harvest weed seed management to be effective, the seeds need to be on the plant at the time of harvest. For weeds like wild oat in spring crops, the seeds are generally gone by that point.
“With a crop that you harvest a lot earlier, there’s a lot more seeds on those plants at the time of harvest. It makes some of those technologies more viable.”
But that’s not to say winter cereals don’t come with their own problems, she added.
“Something like cleavers could be a real problem in winter cereals because they come up and establish at the same time,” said Tidemann.
“We have herbicides to manage those right now, but with the way our herbicide resistance is going, that could be a concern.”