They’re big numbers underscoring a big problem. In Saskatchewan, over 15 million acres of weed patches are resistant to Groups 1 and 2 herbicides. Of 31 known herbicide sites of action, 21 have confirmed resistance to a weed species. And, with 56 confirmed cases, Canada is third in the world for herbicide-resistant weeds.
These are just a few results of a government- and commission-sponsored survey on weeds in Saskatchewan. It can be summarized by this quote from the report: “Given the linear increase in herbicide-resistant weeds, every annually cropped field in Saskatchewan could have at least one type of herbicide-resistant weed species by 2027.”
And barring the discovery of new modes of action — which has been a challenge for some time — expanding use of integrated weed management (IWM) practices may be the only hope for winning the war on herbicide resistance, the weed researcher who led the survey says.
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“If we do not adopt integrated weed management or start integrating other non-chemical practices with our herbicide management programs, we’ll likely see this trend continue,” says Charles Geddes, who works out of Agriculture and Agri-Food Canada’s research centre in Lethbridge.
And of course it’s not just a Saskatchewan issue. While there are some differences in specific weed and management challenges, Alberta and Manitoba each face the same basic state of resistance.
“The story behind wild oat being one of the biggest grassy weed issues and kochia being one of the biggest broadleaf weed issues is generally consistent across the board for the Prairie provinces.”
(Wild oat is the most prevalent herbicide-resistant weed in Saskatchewan overall, showing resistance in 82 per cent of the 250 fields where wild oats were found. It has developed resistance to both Groups 1 and 2. Group 2 resistance in kochia was found in 100 per cent of fields tested representing 39 per cent of fields surveyed.)
Jason Lenz, a grower from Bentley, Alta., northwest of Red Deer, doesn’t consider the 2027 prediction inevitable.
“Farmers are learning pretty fast that resistance in wild oats is becoming more and more widespread and we’re doing what we can to keep those resistant (weeds) from spreading any farther both within a field and making sure that you’re not in any way trying to spread it from field to field.”
READ MORE: Into the weeds: 2024 in preview
Although Lenz is doing all he can to stretch his herbicide as far as he can by boosting seeding rates and spraying early — among other practices — he considers resistance challenges all in a farmer’s day’s work.
“Sometimes you don’t have full control over what happens with weeds and with Mother Nature… In many ways it seems like she’s always ahead of us whether it’s with weed resistance or weather conditions.”
IWM includes the broad range of weed management. Beyond chemical methods, it includes cultural (such as increased seeding rates), physical (weed mowing, harvest weed seed control) and biological (for example, ground beetles eating weed seeds) methods.
‘You’re limited’
All the practices sound good in theory, but no farmer could ever implement every single one, due to unique geographical challenges that limit universal adoption.
The applicability of IWM practices can even differ substantially between central and southern Alberta, where early-season weed growth allows farmers to tackle them before they become established.
Meanwhile, the central Alberta area where Lenz farms features one of the shortest growing seasons in Western Canada. Most years the soil isn’t warm enough for weed germination to take place until the crop is in the ground, limiting pre-establishment management.
Kevin Bender, who also farms in central Alberta, near Sylvan Lake, notes some other regions have crop rotation (an IWM practice) options unavailable to him.
“We can’t do corn or soybean, and unless you have livestock or you’re near livestock there’s no point really in doing silage greenfeed. So certainly geography, I think, helps in certain areas where you have more options, but in other areas you’re limited.”
Sometimes “the right thing” in one aspect of farming isn’t the right thing in another. Tillage, for example, is an old weed management (and IWM) practice that has fallen into general disfavour, thanks to zero- and minimum-till practices that better conserve soil carbon.
However, with caution, tillage can still be remarkably effective as a weed management tool that reduces herbicide use. In some areas, farmers have little choice but to till more than their zero-till counterparts.
Although Lenz approves of zero-till in general, he said it isn’t effective as a primary weed management tool in all circumstances.
“It’s been proven in my part of the world that that some minimum tillage is the best practice,” he says.
“Sometimes when you’re out talking to other farmers and they hear that you’ve got the disk or the cultivator out, they say, ‘Are you sure you need to do that?’ Sometimes that tillage pass has to happen to get rid of some weeds.”
However, one of the most powerful weed management tools might be one that can be done pretty much anywhere: collecting seeds from weeds in the field prior to harvest and testing them for resistance in a lab.
“I’ve done that on our fields in the past, probably four years ago,” Lenz says. “That’s the surefire way to know whether you have resistance or not.”
It may sound trite but it’s true, Lenz says: farmers have to know their farms in order to manage them, and weed management is no exception.
“You have to know what you’re dealing with for sure before you go out and do some tillage and make a decision whether a tillage pass or a herbicide pass is the best one to incorporate.”
Seed control
Harvest weed seed control is growing in profile in the battle against resistance. Impact mills, which grind down weed seeds and send them out the back of a combine — stifling their ability to create weeds — are an example that has become one of Australia’s answers to herbicide resistance. It continues to innovate in that space.
The Harrington Seed Destructor physical impact mill — claimed to feature a 95 per cent weed seed destruction rate — was the focus of a recent AAFC study in which both Bender and Lenz participated.
Both saw potential in the implement — which carries a price of around C$100,000 — but said it wouldn’t be sufficient in areas where wild oats are public enemy No. 1.
“Wild oats go to seed prior to harvest so they’re already on the soil by the time you hit the combine,” says Bender, who added it may work on other weed seeds.
“But I don’t see a great fit for it here. It takes a lot more effort — like power and fuel — to run that machine. If it’s effective, then yeah — it’s probably worth the cost.”
Although they may not solve the wild oat issue, Lenz says there are smaller, less expensive units that accomplish what the Harrington machine does.
The cost of adopting new tech will always be a barrier to early adoption, Geddes says. The eventual availability of “green-on-green” sprayer sensors in Canada will likely bear this out.
“As you see further investment in that technology and in the research behind it, hopefully the cost of implementing it will decline and open up the ability for more farmers to implement some of these technologies.
“But if you’re looking for something that you can implement immediately, integrating some of those non-chemical practices is probably the most viable option.”
