Glyphosate-resistant wild oats are in Australia, and that’s bad news here

Date:02-14-2020

Weed scientists say it’s a matter of when, not if, wild oat populations here will develop resistance to glyphosate — as they’ve now done in Australia. Photo: Manitoba Agriculture

Glyphosate-resistant wild oats have been found in Australia and that should be a wake-up call to any farmer who thinks it couldn’t happen in Canada.

“This is the first confirmed case of glyphosate-resistant wild oats in the world,” said federal research scientist Breanne Tidemann.

“It’s something we’ve been concerned about but no one has ever seen, so there’s always been a little bit of an attitude of, ‘Well, it hasn’t happened yet — how big of a concern is it really?’

“But it has actually happened now, and we’re on that same track to select for it.”

Australia, which is second only to the United States in the number of resistant weed cases globally, typically sees resistance develop before it does in Canada (which rounds out the top three for resistant weed cases globally).

As a result, “we tend to look at them as our warning light for where we don’t necessarily want to go,” said Tidemann.

In this particular case, an Australian farmer found two different species of glyphosate-resistant wild oats in his field — one that luckily isn’t found in Canada, and one that is. And that particular species of wild oats is already causing headaches across the Prairies, she said.

“Wild oat has been our No. 1 problem weed in Western Canada. It costs the most money to manage compared to all the other weeds,” said Tidemann.

“If we were to discover glyphosate-resistant wild oats this coming summer, we would have to start to expect decreased yields.” – Breanne Tidemann.photo: Supplied

A study done more than a decade ago estimated Prairie farmers spent $500 million on wild oat herbicides annually and it’s also been estimated they lose another half a billion from reduced yields, dockage losses, and lower grades.

While no glyphosate-resistant wild oats have been confirmed in Canada, resistance to other selective herbicides is growing, and right now, roughly 50 per cent of the wild oat populations across the Prairies are resistant to Group 1 and Group 2 herbicides.

“So we’re losing our Group 1s and 2s, which means we’re ending up with limited herbicide options already,” said Tidemann.

Glyphosate could soon face the same fate, according to a study conducted by federal research scientist and weed expert Hugh Beckie a decade ago. At the time, Beckie set out to determine which weeds in Western Canada would be most at risk of developing glyphosate resistance. Kochia was identified as one of the top at-risk weeds in both the Grasslands and Parkland regions, and within a couple of years, glyphosate-resistant kochia was discovered.

But in the Parkland region, wild oats were the No. 1 at-risk weed and No. 2 in the Grasslands region.

“The fact that he was so correct on kochia makes this a little scary,” said Tidemann. “When Hugh Beckie predicts something like this, I tend to believe him.”

Herbicide reliance

It’s no surprise that the most troublesome weeds are at risk of developing resistance — the more you spray with a certain product or mode of action, the higher the number of selection events and the greater the likelihood that resistance will develop.

“We started to select for resistance, and basically what we’re seeing right now is the result of our previous weed management choices, as well as some of our current ones,” said Tidemann.

“I would say that, in most cases, our cropping systems rely on herbicides for our weed management, and the more we rely on our herbicides, the more resistance we’re going to continue to see.”

But with few other effective — and cost-effective — control options, farmers have typically had to take a more “reactive approach” to herbicide resistance, only adapting once it occurs.

“Herbicides, for the most part, are very effective, relatively simple to use, and relatively cheap. Any of these other management tactics that we talk about cost money,” said Tidemann.

“A producer still has to be profitable to continue farming, so when they’re sitting down with their books, they’re seeing it’s a lot of money to spend when their herbicide is still working.

“It is reactive, and they tend to adapt when they have to, but I understand their reasoning for that.”

‘Scary’ scenario

But if — or more likely, when — wild oats here develop glyphosate resistance, adapting may mean learning to live with lower yields and profits.

“If we were to discover glyphosate-resistant wild oats this coming summer, we would have to start to expect decreased yields,” said Tidemann. “I don’t think we have a management strategy currently that could compensate for that loss.

“So I would expect we’d start to see yield losses and quality losses in some of our cereals from wild oat contamination.”

And the news only gets worse from there.

Right now, glyphosate allows farmers to rotate to a different herbicide group to extend the life of their Group 1 and Group 2 herbicides.

“If we lose that, that’s a big concern,” said Tidemann, adding that it’s particularly a concern for pre-seed burn-off.

“Wild oat is very competitive with crops if it emerges first. If it emerges three days before the crop, that can really impact the yield of that crop.

“And I suspect that most farmers are relying on glyphosate to manage wild oats when they do their pre-seed burn-off. Losing that as a tool is scary.”

Wild oats also aren’t always a good candidate for management strategies such as harvest weed seed control because of their biology, she added.

“We don’t have great alternative management strategies for wild oats that aren’t herbicides.”

In fields with low populations of wild oats, management practices such as increasing seeding rates or incorporating winter cereals, early-cut silage, or perennial forages in the rotation can keep weed populations low. But if weed populations are heavy, these techniques “aren’t enough to compensate for not using herbicides,” said Tidemann.

Call to action

Avoiding that gloomy future for as long as possible needs to be the priority now — which is why Tidemann and other weed scientists are urging farmers to rethink their glyphosate use.

“Can we prevent it from getting here sooner than it otherwise might?” said Tidemann.

“Are there opportunities to cut down on our glyphosate use and help limit the selection? If you are relying on glyphosate as your pre-seed option for wild oats, is there another product you can put in the tank to target them? If you’re doing pre-harvest applications of glyphosate, are you doing it for perennial weed control or are you using it for desiccation, even though it’s not technically a desiccant? Is there a different product you could use?”

The nearest wheat field in Australia is more than 12,000 kilometres from Alberta. But farmers here need to take the discovery of glyphosate-resistant wild oats there to heart, she said.

“Incorporating as many strategies as you can now before we run into problems is going to be really key.”