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Confronting a common enemy

Herbicide resistance is a familiar battle to Canadian farmers. According to the International Herbicide-Resistant Weed Database, a collaborative effort run by weed scientists across 80 countries, Canada has 56 unique herbicide-resistant weeds, meaning prevention and control methods are more important than ever.

In a recent webinar, hosted by Top Crop Manager and presented by Bayer Crop Science, three members of the Bayer Market Development Agronomy Team joined three producers from Western Canada to discuss on-farm resistance management strategies, best practices and new technologies to protect fields and chemistries.

The current state of herbicide resistance
Canada’s experience with herbicide-resistant weed biotypes is rapidly evolving, with 128 cases of herbicide resistance present across the country, notes Kate Hadley, market development agronomist for Bayer, based in Saskatoon. Many weeds, including kochia and wild oat, are resistant to multiple herbicide groups, and new resistance to Group 9 herbicides is developing in more grassland species, Hadley adds.

To set the scene, Hadley refers to research led by Hugh Beckie, a former weed scientist at Agriculture and Agri-Food Canada and recently retired director of the Australian Herbicide Resistance Initiative. Beckie’s research, published in 2020, presented findings of field trials conducted between 2014 and 2017 to measure levels of Group 1- and Group 2-resistant wild oats across 800 randomly selected fields in Manitoba, Saskatchewan and Alberta. “Almost 80 per cent of the tested samples from Manitoba, and about 60 per cent of the tested samples from Alberta and Saskatchewan, came back with Group 1 resistance,” Hadley explains.

Although Group 2-resistant wild oat is not as prevalent, it is starting to increase, Hadley notes. Between 60 and 65 per cent of products available for cereal grasses are Group 1 herbicides, she adds, commenting on the potential for Group 2 herbicides to help manage Group 1-resistant wild oats. “There’s a really big opportunity for Group 2s to help manage that Group 1 resistance.”

Reducing risk of resistance
Growers must be cognizant of best practices to prolong the lifespan of these important herbicides. Among the list of recommended tactics, says Amanda Fedorchuk, market development representative for Bayer in northwest Saskatchewan, are planting clean seed, increasing crop competition, proper fertility and following label rates and timing.

“Larger weeds in general are harder to control; they’re more likely to metabolize these herbicides and maybe outgrow them,” she says. “Quite often a grower might push a herbicide application by a few days to make sure all the weeds are up . . . unfortunately, those few days mean weeds might be growing to the point that they’re out of stage for label rates, become harder to control.”

Fedorchuk also references the critical weed-free period – in wheat, this is the one- to three-leaf stage. “The critical period of weed control is when you’re really concerned about yield losses due to crop competition. That’s a point in a weed lifecycle that you need to make sure the weed control is maximized,” she emphasizes.

Putting practice into play
For growers, an on-farm resistance management must combine strategic planning with a bit of agility; merging the tried-and-true with some calculated experiments.

Brady Ferris farms about 2,000 acres with family near Radisson, Sask., growing mainly barley, wheat, canola and peas. For Ferris, a good rotation of both crops and different active ingredients is vital. “Depending on how much moisture we get this year, I’m looking into trying some winter annuals to shift some different weed pressures too,” he added.

Quinn Cubbon, who farms about 5,000 acres with his father and uncle in North Battleford, Sask., also prioritizes diversity.

“We have canola, wheat, peas, lentils, barley and oats. Crop rotation allows us to have a herbicide rotation,” Cubbon says, noting that he’s open to other strategies, like proper timing and increased seeding rates. “We also use herbicide stacking, and increase our water volume to get a better overall coverage.”

“We have found over the years that adjusting the pH of our water, prior to mixing our chemical, really helps with the efficiency and the effectiveness of it,” adds Rob Page, who farms about 2,400 acres of peas, wheat, barley and canola (half of which is irrigated) in southern Alberta, alongside his father. “We’ve also slowly been increasing our seeding rate as well, especially on our irrigated land,” he says. “But a lot has to do with timing, and weed staging and scouting fields.”

Rotating a new chemistry into the mix
With ongoing herbicide resistance, scientists are working to introduce new solutions. As Sam Clemis, market development agronomist for Bayer in central Manitoba says: “Part of a good integrated weed management strategy includes the use of tank mixes with multiple effective modes of action.”

One such development is Varro FX, a new cross-spectrum herbicide registered for spring wheat and winter wheat, combining Group 2 thiencarbazone-methyl with Group 4 fluroxypyr to provide control of tough grassy weeds like Group 1-resistant wild oats. As the only emulsifiable concentrate (EC) formulation on the market, Clemis says the product is easy to mix, handle and clean out of tanks and booms.

Like any product, timing is important, and Hadley reminds growers that Varro FX is best applied before jointing, or the presence of the first node. “The best way to check your crop for the proper staging is to get out and scout your fields,” Hadley advises. “The one- to three-leaf stage is the right time to spray Varro FX and get your crop off to a really clean start.”

Varro FX’s unique EC formulation means that it’s not suitable for durum wheat, and should be used in combination with a broadleaf tank-mix partner to target specific weed populations. Clemis reminders growers to pay attention to product labels for recropping restrictions when choosing a tank-mix partner.

“Some options include 2,4-D or MCPA,” notes Clemis, adding that the window of application will vary depending on which tank-mix partner is chosen. “Buctril M or Thumper are good options for kochia up to 10 centimetres,” she adds. “Infinity would provide the largest window of application and would be best for large, tough-to-control weeds like kochia, up to 15 centimetres.”

And although it’s nice to have predictability when it comes to planning an integrated weed management strategy, Fedorchuk advises keeping an open mind when it comes to introducing different chemistries and tactics.

“The sooner you introduce different herbicides and modes of actions, the better – it really prolongs the lifespan of your products,” she cautions. “When you break it, you can’t fix it.”

Watch a recording of the webinar for more insights from the Bayer Market Development Agronomy Team and farmer panel, and learn more about Varro FX here.