Danny Dion describes the stack of failed expectations and mistakes that caused a 600-acre field to become overrun with herbicide-resistant (HR) wild oats. It will take them years to fix the mess.
A big culprit was a sprayer model Dion bought on the promise of exceptional weed control with only 2.75 gallons per acre of water and 75 per cent of the recommended herbicide rate. Horse feathers.
“I realized years later that it was a sales pitch, and it was the beginning of my problems with wild oats,” says Dion, who farms with his son, Tarren, near Donnelly, Alta., in the Peace River region.
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The same herbicide groups applied “over and over again” also contributed, he says, and so did a change in their crop rotation. The Dions used to produce alfalfa for the export processor at Falher. The perennial crop stayed in production for three or four years, providing exceptional weed competition. Then the processor closed, and alfalfa went out of the rotation. The rotation is now primarily canola and wheat, with some peas.
Dion then strung together another short list of competition killers that allowed the resistant population to explode. Peas drowned out during a couple of wet years, and wild oats filled all those empty spaces. Same thing with seeder misses. He also recalls the times the sprayer was “not purged properly” and applied only water for several acres.
All these activities, stretched over 20 years, produced a massive seed bank of wild oats with resistance to a long list of herbicides.
Test results
Calvin Yoder, a specialist with the local research organization SARDA and Peace Region Forage Seed Association, collected wild oat seeds on that field in 2022 and 2023. He sent them to a lab for herbicide-resistance testing.
“Never make assumptions,” Yoder says. “Lab testing is crucial for developing a long-term plan in terms of future crops and herbicide options.”
The tests revealed a field of super-powered wild oats.
Results from 2022:
• 97 per cent of sampled wild oats were resistant to Group 1-fop chemistries (e.g. actives in Puma Advance and Assure II)
• 72 per cent were resistant to Group 1 pinoxaden (e.g. active ingredient in Axial)
• 70 per cent were resistant to Group 1 tralkoxydim (e.g. Achieve L)
• 37 per cent were resistant to Group 1 clethodim (e.g. Centurion)
• 98 per cent were resistant to Group 2 flucarbazone (e.g. Everest)
Results from 2023:
• 100 per cent of sampled wild oats were resistant to Group 1-fop chemistries
• 76 per cent were resistant to pinoxaden
• 28 per cent were resistant to clethodim
• 86 per cent were resistant to flucarbazone
• 87 per cent were resistant to Group 2 thiencarbazone (e.g. Velocity)
• 86 per cent were resistant to Group 2 pyroxsulam (e.g. Simplicity)
Many key tools were now off the table, but at least the Dions knew what they were up against.
Like a strict fitness routine
So where does a farmer begin to exorcise those demons?
Dion now invests serious time and money in herbicide-resistant weed management, using expert help from SARDA staff as well as Kristina Polziehn, owner of Axiom Agronomy. She is the weed management equivalent of a fitness instructor.
“If you want results, make a plan and set goals,” Polziehn says. “It can take seven to 10 years to fix these fields. You can have great results after a couple of years, but you have to stay on top of it.”
A field can quickly backslide if you give weeds any shot to set seed in big numbers.
Fall herbicide is a good proactive step, Polziehn says, and it requires a firm commitment to next year’s rotation. Fall herbicide choices have to mesh with the following crop. Canola seedlings, for example, tolerate only a specific few herbicides applied in the fall.
If the Dions decide on wheat for next year, Polziehn would recommend a fall application of Focus, a herbicide that includes Group 15 pyroxasulfone and Group 14 carfentrazone-ethyl.
“The Group 15 product at the 136-millilitres-per-acre rate has good residual on their soil type for wild oat in the spring,” Polziehn says. The Dions have not used these actives on that field, she adds.
If the Dions decide on faba beans or peas, crops they grow less often due to markets (faba beans) and aphanomyces (peas), they could use Edge in the fall.
In the spring, just before seeding, Dion has also tried Avadex.
“It works, but not always 100 per cent,” he says. “It works best with blackened soil, little to no straw and half an inch of rain right after application.”
To improve results, he harrows in the fall and again in the spring before applying Avadex.
Use canola HR systems to their full advantage
With Liberty Link canola, Polziehn encourages farmers to make their second pass with higher rates of Liberty and full rates of clethodim. The second application is often a challenge, she says, when spraying season is long and farmers are tired and burned out.
“Some clients always budget for a second pass to ensure weed seed production is managed, despite no yield advantage,” Polziehn says.
When growers use TruFlex, Polziehn encourages them to take full advantage of the multiple application option. She says the TruFlex system is great for herbicide-resistant wild oat management.
The Dions grew TruFlex canola on the 600-acre field in 2025. They sprayed it four times and it was “super clean,” Dion says, “but Tarren was getting sick of spraying that field.”
Is it possible to select for glyphosate-resistant wild oats? “Yeah, probably,” Dion says. “But I’m not worried about it at this time.”
Yoder adds a few specific tips for TruFlex: Use the 333 ml rate over multiple applications, and use higher water volumes — like 10 gallons per acre — when the canola is to starting to canopy.
Bayer advises that applications should be 10 days apart; the total rate for the year cannot exceed 1.33 litres per acre total; and do not apply beyond first flower. The company adds that the 333 ml rate is appropriate for wild oats, but perhaps not all weeds. Know the weed spectrum and apply appropriate rates for those weeds. Finally, Bayer notes that canola cultivars with stacked Liberty Link and TruFlex offer added opportunity to rotate herbicides.
“Multiple applications might be expensive in the short term but will pay dividends in the long term,” Yoder says. “TruFlex canola provides the best opportunity to start managing fields with high levels of herbicide-resistant wild oats, so take advantage of the opportunity.”
Part of the problem in 2025 was a dry start that slowed canola crop establishment in the field. Canola emerged in patches, with some three to four weeks later than the first emerged plants.
“The wild oats kept filling in those open spaces with new flushes,” says Dion.
Polziehn hopes this aggressive approach with the TruFlex system in 2025 will reduce the Dions’ wild oat numbers and eliminate some of the biotypes with broad-spectrum resistance. She plans to test seed from random escapes. She captures samples with an insect sweep net when seeds are mature and just about to drop.
Polziehn recommends weed seed tests to identify the resistance biotypes in a field. She sends seed samples to the Ag-Quest lab in Manitoba (see sidebar.) Tests are specific to each herbicide active ingredient. At $135 per test, testing numerous active ingredients can add up, but an accurate picture of products that work will lead to improved weed control decisions.
Scout closely
While testing is an important step to know what products should work, growers also need to scout before spraying and again a few weeks afterward to see how the herbicides performed.
Performance is not always as obvious as you might think. One of Polziehn’s farmer clients applied Edge last fall to a field planned for pulses this year, yet the crop still had a lot of wild oats. Turns out these wild oats were all germinating from below the herbicide layer.
“These were very determined wild oats,” she says. The fact they germinated and the farmer sprayed them in-crop did take a step toward reducing the wild oat seed bank — an important step in the long-term management program.
Expand the circle with spot sprays
Farmers may be inclined to spot-manage a patch of herbicide-resistant weeds, especially when soil-incorporated herbicides are $30 per acre.
Polziehn has specific concerns and recommendations for spot applications: Plants often get missed if the target area is too small, and those few misses can refresh the seed bank and perpetuate the problem.
Instead, she makes the spray area much larger than the patch. If the patch is two acres, she will spray 15 to 20 acres around it, then scout after to see that everything was controlled.
Be determined
Once a population of herbicide-resistant weeds has taken over a field, farmers need a long-term plan and a gym-rat level of patience and determination.
Dion knows they’re in for the long haul. “The wild oat seed bank in that field is banked hard,” he says.
