Seventy-two per cent of fields surveyed in the federal-provincial project — one of three surveys measuring herbicide resistance in Manitoba, Saskatchewan and Alberta — were found to have at least one type of resistance. Those fields comprised 3.7 million acres of cropland throughout Manitoba.

The percentage grew slightly compared to a similar survey in 2016, when 68 per cent of fields were discovered with herbicide-resistant species. Previous surveys in 2008 and 2002 saw herbicide resistance in 48 and 32 per cent of fields, respectively.

The survey reported that the final bill to the province’s farmers — when factoring reduced crop yields, quality and higher weed management expenditures — was $77 million per year.

Resistance marches on

Unsurprisingly, Group 1 and Group 2 herbicide resistance marched on since the last survey in 2016, says participant Charles Geddes with the Agriculture Canada Lethbridge Research and Development Centre in Alberta.

The survey report called the further adoption of integrated weed management practices among growers “critical” to reducing resistance.

Geddes has mixed feelings on this point because he recognizes the extent Prairie farmers are already using practices such as crop rotations and increased seeding.

“What these surveys suggest is that herbicide resistant weeds continue to increase in their impact, regardless of the practices that are being currently used to manage them.”

Charles Geddes
Agriculture Canada Lethbridge Research and Development Centre

Geddes is finding pockets of producers fighting herbicide resistance with herbicide diversity practices such as mixing modes of action.

A 2017 paper by now-retired Agriculture Canada researchers Hugh Beckie and Neil Harker warned farmers about relying too much on herbicide diversity at the expense of integrated weed management. The paper argued that crop diversity — including a mix of dicots and monocots, winter and spring planted, and annual and perennial crops — exerts different selection pressures on weed communities that herbicide diversity alone cannot replicate.

Some resistance up, some down

The pre-harvest survey occurred in 2022 and included 155 annual cropped fields. Five hundred and eighty-four mature weed seed samples were collected from all visible uncontrolled weed patches and tested for resistance to Group 1 ACCase, Group 2 ALS and Group 9 glyphosate. The samples represented 44 weed species.

“Compared to the previous 2016 survey, a trend toward increasing ALS inhibitor resistant broadleaf weeds and decreasing herbicide-resistant grasses was observed, with some exceptions,” read the report.

Thirty per cent of all fields surveyed featured wild oats with resistance to the Group 1 and Group 2 herbicides. Among other grassy weeds, 27 per cent of all fields surveyed had Group 1-resistant green foxtail, while 12 per cent included Group 1-resistant yellow foxtail.

Notable among broadleaf weed resistance were kochia (19 per cent Group 2 resistance in all fields surveyed), pale smartweed (10 per cent Group 2 resistance) and redwood pigweed (nine per cent under the same metrics).

Eleven herbicide-resistance weed species were logged, including four not found in the 2016 survey: ALS inhibitor-resistant common chickweed, pale smartweed, Powell amaranth and spiny sowthistle.

Fewer patches, more fields

An interesting factor in the survey, says Geddes, was a decrease in uncontrolled herbicide resistant weed patches compared to the 2016 Manitoba study — even as the number of fields with resistance increased slightly.

“Patch area is representative of site-specific weed management scenarios, whereas the field area is more representative of a broadcast style weed management program where they would be applying a herbicide across, say, an entire field to manage this issue,” Geddes says.

In short: patches and the area they occupied were lower in 2022 than in 2016, but more fields had herbicide-resistant weeds in them overall.

Geddes thinks this is a call to farmers to manage weeds more at the patch level rather than the entire field.

“One big thing that kochia has taught us is that it’s highly patchy and it tends to infest those low lying and saline patch areas first and then move out into the rest of the field,” he said.

“So there’s a lot of opportunity for things like patch management and maybe reducing the cost of integrated weed management by targeting the areas where it makes sense.”

Alberta next

This series of resistance surveys occurs every few years in all three Prairie provinces. They were pioneered by Beckie, who worked at the Agriculture Canada Saskatoon Research and Development Centre in Saskatchewan.

The Alberta survey report is tentatively scheduled for publication later this year, says Geddes.

“The manuscript is almost ready to be submitted. We’re just kind of doing some of the final touches on it, and then it’s up to the review process, which can take several months, but it should be sometime this year.”

Three other Agriculture Canada Lethbridge researchers also participated in the Manitoba survey: Mattea M. Pittman, Kim Brown and Julia Y. Leeson. Other contributors included Manitoba Agriculture in Carman and Agriculture Canada Saskatoon.

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That was the core message Brendan Metzger delivered at the Manitoba Agronomists Conference.

The chemistry itself, he said, has not suddenly changed. What has changed is the cropping context around it, particularly as glufosinate moves into systems that expose management mistakes more quickly and more consistently.

WHY IT MATTERS: With glufosinate use expanding on the Prairies, careful management will matter more in slowing resistance pressure.

Metzger, a senior herbicide biologist with BASF, said the risk facing Liberty is real and accelerating. Glufosinate resistance has already emerged in other regions, and Prairie farmers are now using the product in crops and rotations that strip away many of the safeguards that once kept resistance at bay.

Reports of glufosinate-resistant waterhemp in several U.S. Midwest states and kochia escapes being reported in North Dakota, suggest resistance is now close at hand.

Liberty still works, he said, but the margin for error is narrowing.

Glufosinate longevity

To understand why management now matters so much, Metzger first walked agronomists through why glufosinate avoided resistance for so long in Western Canada, especially when compared to glyphosate.

Glufosinate was introduced in the mid-1990s, at roughly the same time glyphosate-tolerant crops entered the market. Yet while glyphosate resistance emerged relatively quickly, Liberty avoided that outcome for nearly 30 years.

“It’s been largely a success story,” Metzger said.

“There’s been no documented cases of resistance to glufosinate in Western Canada.”

He said that longevity had little to do with glufosinate being inherently resistance-proof. Instead, it reflected how and where it was used.

For much of its commercial life, glufosinate lagged behind other herbicides in total acres treated. Lower overall use meant lower selection pressure on weed populations. Just as importantly, most glufosinate applications in Western Canada occurred in canola.

Canola’s competitiveness played a quiet but critical role.

Rapid early growth and quick canopy closure suppressed escapes and reduced the number of weeds exposed to sub-lethal doses. That cultural weed control helped mask small mistakes that might otherwise have contributed to resistance.

“So we have the cultural weed control aspect working in our favour as well,” Metzger said.

Rotation added another layer of protection. Even in relatively simple canola–wheat systems, glufosinate was rarely applied back-to-back on the same acres. Breaking up modes of action further reduced resistance risk.

Those factors combined to give Liberty a long runway, Metzger said, but that runway is now shortening.

Competition pressure

Metzger warned that as soybean acres expand, so will selection pressure on glufosinate.

While Liberty-enabled canola already accounts for a large share of Prairie acres, Metzger said the more consequential shift is happening in soybeans as seed companies move aggressively toward glufosinate-tolerant platforms across North America.

Roughly a quarter of western Canadian soybean acres are expected to be Liberty-enabled in 2026. Metzger said that expansion is being driven largely by widespread glyphosate resistance, with glufosinate long viewed as a relatively underused alternative.

Unlike canola, soybeans are far less competitive.

Wider row spacing and slower canopy closure mean fewer escapes are hidden. Weeds that survive an application are more likely to remain visible, reproduce and contribute seed back to the soil.

Corn shares some of those same characteristics. In those systems, Metzger said, poor management is more likely to translate directly into resistance risk.

Another concern for Liberty is that its mode of action amplifies the consequences of poor application.

Glufosinate is a contact herbicide. It only affects weeds it lands on, and those weeds must receive a lethal dose to be killed. That makes the product especially vulnerable to sub-lethal exposure.

“A sub-lethal dose, whether that means not adding enough product to the sprayer or not getting it to the target at the proper dose, can select for resistant individuals over time,” said Metzger.

Risk management

Delta T, which relates spraying conditions to air temperature and humidity, is particularly important for water-based formulations such as Liberty, said Metzger.

Compared to oil-based products, glufosinate droplets take longer to cross the leaf cuticle, increasing the risk that moisture evaporates before the active ingredient can move into the plant.

Metzger said Liberty remains an effective tool, but he cautioned against assuming it will behave the same way it did when most acres were in canola.

As more soybean and corn acres shift toward glufosinate tolerance, resistance risk will be shaped less by the chemistry itself and more by how consistently it is managed.

Coverage, timing and weed size are no longer details to fine-tune, Metzger said. They are the difference between preserving the tool and quietly selecting for trouble.

Liberty still works, but on today’s Prairie farms, it no longer forgives mistakes.

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Kochia, a long-time headache for southern Manitoba farmers, is now popping up as far north as Foxwarren and Dauphin, said Jeanette Gaultier, a technical services specialist at BASF.

“It’s just an ongoing issue. It’s there,” Gaultier said at Manitoba Ag Days 2025.

WHY IT MATTERS: Kochia is no longer confined to southern Manitoba, advancing north at a rapid pace, and has a biology seemingly primed to overcome herbicides farmers might come to rely on to control it.

More than a decade ago, Agriculture and Agri-Food Canada (AAFC) scientists predicted kochia’s northward march as they modelled how warming temperatures would affect weed distribution.

“I can say that their predictions are absolutely true,” Gaultier said.

The weed’s spread is compounded by growing herbicide resistance. Farmers can already assume Group 2 and Group 9 herbicides won’t work on Manitoba kochia populations, experts warned. Small pockets of Group 4 resistance exist, but have been thankfully slow to spread.

More concerning is the rapid progression of Group 14 resistance. About 20 per cent of tested kochia populations now resist Group 14 herbicides, according to recent findings from AAFC researcher Charles Geddes. This chemistry has been crucial for controlling the weed in recent years.

There is also new concern over Group 10 resistance pushing up from the south. At St. Jean Farm Days in early January, North Dakota weed specialist Joe Ikley noted they have been seeing more kochia escapes after being sprayed with glufosinate.

“We see escapes almost every year,” Ikley told attendees of that farm show.

“Can we prove those ones to be resistant, yet? It’s just a matter of time … until we get a population that is indeed resistant.”

For managing kochia, farmers must shift to multiple modes of action that actually work, not just tank-mixing products when only one is effective, Gaultier said.

Effective options include Groups 3, 4, 5, 10, 14 and 27 products used in combination programs. Group 15 herbicides offer some suppression when mixed with other products.

Mechanical control another strategy

Beyond chemicals, Gaultier praised farmers who are taking physical action against kochia patches.

“I was pleasantly surprised this fall driving around and how much mowing I saw of patches,” she said. “This is amazing. We are throwing in some non herbicides with some cultural management. This definitely prevents seed set.”

One farmer even bailed and burned kochia patches.

“I think this is a great way to help. You’re probably still getting some seed set, but it’s helping,” Gaultier said.

Kochia requires a proactive approach starting with pre-emergent herbicides, according to Manitoba Agriculture weeds specialist Kim Brown.

“With kochia, you have to be proactive versus reactive,” Brown said at Ag Days.

She recommended products like Authority and Valtera, which can be applied as pre-emergent residuals, or products like Authority Supreme, Fierce or Voraxor Complete.

Pay attention to application instructions

For Liberty applications, Brown stressed the importance of proper water volume, a point that cannot be compromised.

The recommended label rate in Enlist corn and soybeans for Liberty 200 SN is 1.0 litre of product combined with 2.4 litres of liquid ammonium sulphate (AMS), applied in 20 gallons of water per acre.

“That is not negotiable. That is how you use that product is a contact herbicide. You have to give it every chance you can to make it work,” Brown said.

She also warned against spraying kochia too late, even with effective products. She described a field where glufosinate initially killed kochia, visible as “burnt, crispy bits,” but the weed regrew because of timing and lack of crop competition.

Crop competition can cut kochia pressure

Kochia has the advantage of early emergence; and heat, drought and salt tolerance. It also spreads seed moderately well. But the weed has weaknesses too. It’s not very competitive against established crops, and seeds’ lifespan in the soil short-lived at just two to three years.

“It has a really short seed bank, and this one maybe helps us, maybe not,” Gaultier said.

Brown presented research from Geddes showing how cultural practices dramatically reduce kochia pressure.

In a four-year rotation of wheat-canola-wheat-lentils, simply narrowing row spacing from wide rows to nine-inch rows and doubling wheat seeding rates made a stark difference: an 80 per cent decrease in kochia biomass and a 63 per cent reduction in the seed bank.

Switching from spring wheat to winter wheat in the rotation proved even more effective. Winter wheat emerges early enough to compete with kochia right from the start.

“This winter wheat comes up first thing in the spring. Despite the fact that kochia is a warm season weed, it is up really, really early,” Brown said. “Something like winter wheat can compete quickly.”

Adding a short-term forage crop like alfalfa/meadow brome, where the crop is cut before seed set, is also a good option.

“Winter wheat reduced biomass by 64 per cent, and by putting alfalfa/meadow brome, it took out 99 per cent of the kochia,” she said. “So if you could make that work, that is a really good option.”

Northern farmers urged to remain vigilant

The message for all Manitoba farmers, but especially those in central and northern regions: keep your eyes open.

“Even if you live north of the No. 1 (highway), the further north you go, keep watching for kochia,” Gaultier said.

“Just even driving around, people are seeing in the ditches some of the kochia,” she said. “I think in the south, I probably have a pretty good idea where kochia is. It’s everywhere.”

— With files from Robert Arnason

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The partnership pairs Geco’s predictive mapping tools with Gowan’s line of soil-applied herbicides in a collaboration aimed at helping farms take a more deliberate, patch-based approach to weed control over multiple seasons.

WHY IT MATTERS: Seeing weed pressure ahead of emergence can make herbicide decisions more targeted and cost-effective.

Geco’s announcement includes two offerings tied to the partnership. The company is launching a new three-season predictive-mapping subscription, and growers who sign up through a Gowan representative will receive one additional field map at no extra cost.

“Our technology enables the question: If you could know where your most problematic patches are and where they are spreading to, what could you do differently? That’s what our technology makes possible,” said Greg Stewart, CEO of Geco.

How predictive mapping works

While blanket applications and spot sprayers respond to weeds already visible in-season, predictive mapping works ahead of emergence by using multi-year imagery to identify the areas most likely to develop patches. That allows farms to be proactive with treatments, rather than reacting after they’ve already gained ground.

A grower wanting a map begins by sharing a field boundary with Geco, often through a platform like John Deere Operations Center. If they don’t have a boundary available, Geco can make one for them. From there, Geco pulls every usable satellite image of that field from the last five growing seasons and runs them through tools designed to distinguish crop from weeds across the full season.

That multi-year history is what drives the prediction. Stewart said the key isn’t ultra-high-resolution imagery as much as having dozens of images per season and several years of history to reveal how weed patches shift over time.

The history shows where weeds tend to emerge early or flush late, and where patches persist. The resulting prescription can be exported straight into a sprayer, granular applicator, drill or variable-rate seeding tool.

“We look at a field, understand where weeds have been and where they’re going, and from there the farm decides what to do,” he said.

Geco has calibrated its system by comparing predictions against drone imagery, spot-sprayer data and human scouting across many fields.

Because the algorithms used to make these calibrations and predictions are proprietary, Stewart was tight-lipped about their inner workings. But while they play a big role in the process, he says the real challenge is fitting the technology into a farmer’s season.

“It’s not usually the math that breaks these technologies,” he said. “It’s how well you solve a real-world problem.”

That means making sure the system fits farm reality. It must mesh with timing at the end of the season and fold naturally into a grower’s weed-control plan. Those practical points tend to matter more than the complexity of the algorithm.

That’s also where partnerships come in. Predictive maps don’t work in isolation; they need to line up with the herbicides and practices growers are already using in the field.

Many early adopters were already using chemistries such as ethalfluralin and triallate (the active ingredients in Gowan’s Edge and Avadex) on their worst kochia and wild-oat patches. Those products are expensive to blanket across entire fields, and predictive maps help target them only where they’re most likely to deliver a return. So, the collaboration made sense for both companies.

But herbicides are only one part of the equation, said Stewart. Once the map is made, growers still need a plan for how to use it: which products to place where, when to increase seeding rates and how to tackle the “problem-child” areas that keep showing up year after year.

“It’s the agronomist and the farmer who put together that strategy,” he said.

For Warkentin, predictive mapping works best on fields with well-defined patches like those same “problem-child” zones mentioned by Stewart. Once he receives a map, he reviews it with the grower to confirm the predicted zones match field history and scouting. He then adjusts rates, creates the prescription file and loads it into the sprayer or applicator.

There are still some practical limits — the kind Stewart refers to when he talks about real-world barriers. For example, some older spreaders can’t run prescription maps. Fortunately there is an easy workaround: growers can load the files into Google Maps. However, Warkentin says timing is a more stubborn problem for farmers.

“The best time to look at these maps is after harvest, but that’s also the busiest time of year,” he said. “By the time fall work is done, there’s very little time left to get maps made up and implemented.”

For farms using higher-value soil-applied products, the economics work well. Targeting only the worst 20 or 30 per cent of the field makes premium herbicides more economical and reduces total chemical use. Farms using lower-cost products may see less financial benefit, since the price of generating a prescription can outweigh the savings from variable-rate application.

However, Stewart noted that most growers use the maps to intensify control in the toughest patches — not necessarily to cut total inputs.

Either way, Warkentin says growers who used the maps were pleased with the results.

“The system isn’t perfect, and producers know there will be a few small misses,” he said. “But overall the people who’ve used it have been happy with the results.”

For weed scientist Charles Geddes of AAFC Lethbridge, predictive mapping fits within a broader integrated weed management approach. He sees it helping growers make more deliberate decisions about where to invest their time, herbicides or cultural practices.

“I see this as another tool in the toolbox farmers have at their disposal,” he said.

Weed pressure is becoming harder to manage due to expanding herbicide resistance and weather variability that affects herbicide performance. Geddes says predictive mapping can help farmers plan where residual herbicides or added competition may provide the biggest returns. Using herbicides that stack multiple modes of action can be costly, especially on dryland farms, and applying them across full fields isn’t always justifiable.

“Predictive mapping lets farmers target herbicides or other practices where they’ll have the greatest impact,” Geddes said. “That can go a long way toward managing both costs and resistance.”

He also notes the technology adds some complexity. Prescription mapping requires growers to manage another layer of planning at a time of year when workloads are already heavy. That may limit adoption for some operations. But he expects interest to grow as farms gain experience and as more tools in crop production move toward AI-driven decision support.

That Prairie focus shapes where the technology goes next. Stewart says the company is now putting more emphasis on building partnerships with local retailers, agronomists and farmers to support longer-term, multi-season weed strategies. The Gowan partnership is just one example.

“We’re starting to partner with other retailers and independent agronomists across the region,” he said. “We’re really developing those relationships as much as we can these days.”

The post Predictive weed mapping, coming to a farm field near you appeared first on Manitoba Co-operator.

These are the facts, Manitoba Ag Days attendees heard during the 2026 show:

Wild oat pressure is increasing across Manitoba. Herbicide resistance widespread.

WHY IT MATTERS: They don’t have as much hype as kochia or waterhemp, but herbicide resistant wild oats are a quieter threat that continues to gain ground in Manitoba farm fields.

Weather patterns in recent growing seasons have favoured the weed, particularly outside of the Red River Valley, according to Jeanette Gaultier, technical specialist with BASF Agricultural Solutions Canada.

“In the last two years, there has been an uptick in wild oat, which is always problematic, but it just seems to be really loving the springs that we’ve had and really taking advantage,” she told the Ag Days crowd.

Even more worrying is the number of wild oats coming back as doubly resistant —neither Group 1 or Group 2 products are doing the trick anymore. The last province-wide weed survey, with data collected in 2022, found that every one of the 155 fields sampled had wild oats resistant to Group 1, and Group 2 resistance wasn’t far behind. A whopping 82 per cent of samples were resistant to both Group 1 and Group 2.

“So, the numbers are against you,” Gaultier said.

She cautioned, however, against assuming all products in those larger groups are useless. Resistance expression can vary.

“There is some variable, with lots of different mutations for these resistances, and you do get variable cross resistances,” she said.

Reducing seed set remains critical, particularly given the cost and limited availability of effective herbicides. Soil-applied products are increasingly important, since post-emergent options are limited.

Crop choice and rotation can also play a role, especially in crops that mature earlier.

“Growing something like peas or fall rye and winter wheat is actually a really great strategy, because you are actually capturing a lot of those seeds,” Gaultier said.

“There are no other post emergent options for wild oats, other than Group 1 and Group 2, but basically… the Group 1s and Group 2s are there, and they’re not working so good,” she said.

Brown also pointed to older cultural practices that farmers might associate more with their parents or grandparents, before modern herbicides were widely available.

Those forebears “used to delay seeding, used to do a bunch of tillage,” she said. “They didn’t have herbicides back then. And then, you seed later. The crop comes up fast and gets ahead of the wild oats.”

However, Brown and Gaultier agreed that no single tactic will solve the problem, and wild oats must be managed as part of a broader, integrated approach.

For more Manitoba Ag Days coverage, watch the Co-operator’s Ag Days landing page.

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Local agronomists are on watch for if those Group 27 chemistries start to slip. That’s on top of Group 14 resistance bubbling in key problem weeds and mounting resistance against several other herbicide groups, noted Kim Brown, weed specialist with Manitoba Agriculture.

While not yet at crisis levels seen in parts of the U.S., experts say the warning signs of increased pressure on locally used herbicides are clear.

WHY IT MATTERS: Growing herbicide resistance, and new weed threats infamous for developing resistance, continue to take key weed control tools off the table for farmers.

While HPPD resistance is more commonly discussed in the context of U.S. corn and soybeans, Brown said Canadian growers cannot assume they are insulated.

Some of the worst weed offenders for developing HPPD herbicide resistance are already here. Palmer amaranth (known in the U.S. for resistance to Groups 2, 3, 5, 9, 14 and 27) was first found in the province in 2021.

It hasn’t taken root as much as waterhemp has though. Waterhemp, which was showing Group 27 resistance in Quebec already in 2020, was downgraded to a Tier 2 noxious weed last year in 28 Manitoba municipalities where the province considers it too established to eradicate.

“We certainly don’t have the waterhemp problem that the U.S. does,” Brown said, although local spread has been enough to launch waterhemp to the top of many a weed meeting agenda.

According to the Manitoba Crop Alliance, local waterhemp has shown resistance to several herbicide groups, “including combinations of Group 2, Group 9 and Group 14.”

The weed is also known for Group 5 resistance in parts of North America and, most recently, Group 10 resistance was reported in the U.S. Midwest.

Complicating matters, resistance testing only shows whether resistance is present at the group level, not whether every product in that group will fail.

“We know we definitely have glyphosate resistance,” Brown said of Manitoba’s locally observed kochia resistance problems.

“Group 2s haven’t worked in years. We’ve got increasing Group 4 resistance, and of course, we have this growing Group 14 resistance.”

There have been a handful of herbicides released in recent years looking to slip through some of the few remaining cracks in its armour. Several products, approved for select cereal crops, have leaned on Groups 6 and 27 to get the job done.

Waterhemp biology raises stakes

Like kochia, waterhemp’s biology makes it a formidable foe.

“This is not a weed that can go away just simply because of the sheer number of seeds that it returns to the soil,” Brown said. “So even if you let a few plants get away, that weed can grow. It can get across the whole field really, really quickly.”

So far, Manitoba has avoided the widespread yield losses seen farther south.

“We’re not seeing the train wrecks that other people in other places have seen,” she said. “But unfortunately, with a weed like that, it can get there fast.”

“We really have very, very few products, if any, once we start seeing full blown Group 1 and Group 2 resistance,” she said. “There’s no other groups that we can use post-emergent to control wild oats.”

From 2019 to 2023, Agriculture and Agri-Food Canada and provincial agriculture departments surveyed herbicide resistance across the Prairies. Manitoba joined the effort in 2022 as part of a provincewide weed survey.

Researchers collected grass weed seed from 155 Manitoba fields and tested them against Group 1 and Group 2 herbicides. All wild oat samples were resistant to Group 1, and 82 per cent were resistant to both Groups 1 and 2.

And the weeds were widespread. Across more than 700 fields surveyed, 37 per cent had wild oats resistant to Group 1 herbicides. Thirty per cent had resistance to Group 2, and 30 per cent had wild oats resistant to both.

This pattern is consistent across the region, according to a 2025 interview with Charles Geddes, a national research scientist in weed ecology and cropping systems based in Lethbridge, Alta.

Researchers have seen herbicide-resistant weeds become more common over time. In 2022, 75 per cent of surveyed fields had at least one herbicide-resistant weed, up from 68 per cent in the previous survey, which covered fewer fields.

“It’s not something we’re going to get done this year,” said Matt Inman, technical marketing manager with BASF. “We have to look three or five years down the road.”

Resistance in highly prolific weeds like waterhemp and Palmer amaranth has reshaped weed control programs across much of the U.S.

“A million seed on one female plant,” Inman noted, citing one of the major challenges with those pigweed species. “You’re dealing with that for years.”

Both Brown and Inman emphasized that herbicides alone will not solve the problem.

“We have to look beyond that,” Inman said. “We have to look at cultural practices, mechanical practices, physical practices, some cover crops, maybe seeding rates. We want that canopy to close as quickly as possible.”

Application practices also matter, including using the right rate, volume of water, spray tips and timing, Inman said.

“We have fabulous researchers at Ag Canada (Agriculture and Agri-Food Canada),” Brown said. “But again, there’s only four of them for all of Western Canada, and there’s absolutely nobody in Manitoba.”

With resistance becoming more complex, including both target-site and metabolic resistance, Brown said farmers increasingly rely on information from nearby U.S.

The post The looming threat of HPPD herbicide resistance appeared first on Manitoba Co-operator.

Aaron Hager, a University of Illinois weed scientist, reported last month that Illinois had several locations where waterhemp had developed resistance to glufosinate, a commonly used herbicide in North America.

WHY IT MATTERS: Weed experts in Manitoba are closely watching the spread of our own waterhemp issues.

Other states in the Midwest have the same problem.

“Four states in the U.S. (including Illinois) are all going to come out (soon) with glufosinate-resistant waterhemp,” said Joe Ikley, a weed scientist at North Dakota State University.

Ikley made the comment Jan. 7 at St. Jean Farm Days, a farm show in Manitoba’s Red River Valley.

The news from the U.S. Midwest is concerning because farmers are running out of options to control waterhemp, a member of the pigweed family. It has already developed resistance to seven different modes of action.

For farmers on the northern Great Plains, it’s a matter of time before waterhemp with resistance to glufosinate is confirmed, Ikley said.

“If it can evolve resistant to a herbicide in Illinois, there’s no reason it can’t do it in North Dakota or the Canadian Prairies.”

Kochia next?

Waterhemp was first discovered in Manitoba in 2017, and it’s now present in a wide geography within the province.

It hasn’t been confirmed in Saskatchewan, but weed experts are asking farmers and agronomists to maintain a close watch for the troublesome weed.

While waterhemp is an extremely difficult weed, a bigger risk to western Canadian farmers would be glufosinate-resistant kochia.

In North Dakota, farmers apply glufosinate to 10 million acres of land every year, Ikley said.

So, kochia plants are receiving repeated doses of glufosinate, and resistance is on the horizon.

More North Dakota farmers are reporting escapes, where the herbicide fails to kill a kochia plant. If glufosinate is applied to 100 kochia plants in field and 95 die, the remaining five plants are “escapes.”

“We see escapes almost every year,” Ikley said.

“Can we prove those ones to be resistant, yet? It’s just a matter of time … until we get a population that is indeed resistant.”

It’s impossible to predict when glufosinate-resistant kochia will arrive in North Dakota or the Prairies.

But Ikley is particularly worried about canola growers, who rely on glufosinate to keep weeds in check.

InVigor hybrids dominate the canola acres in Western Canada, which are genetically modified to have tolerance to glufosinate.

“The issue, when I look at kochia and canola right now, is that the options are glyphosate or glufosinate,” Ikley said.

“And we (already) have widespread glyphosate resistance (in kochia).”

At St. Jean Farm Days, an agronomist delivered a blunt assessment of the risk.

If glufosinate-resistant kochia appears on the Prairies, farmers are “hooped.”

The post Glufosinate-resistant waterhemp found in U.S. Midwest appeared first on Manitoba Co-operator.

Escapes of the tenacious weed were back in grain fields this year, despite the annual spring and in-season efforts to blitz spray them out of existence.

WHY IT MATTERS: Wild oats may not carry the red alert alarm of new noxious weeds like waterhemp, but they’re a widespread weed headache well known for shaking off chemical controls.

“The single biggest issue with wild oats is resistance,” said Manitoba Agriculture weed specialist Kim Brown. “If we lose …our ability to use Group 1 and Group 2 because of resistance, you have no in-crop products left.”

That double resistance is becoming distressingly common.

Between 2019 and 2023, Agriculture and Agri-Food Canada and provincial ag departments embarked on an effort to measure herbicide resistance levels on the Prairies. In 2022, that survey came to Manitoba as part of a larger study of weed abundance across the province.

The resistance survey involved gathering, planting and spraying grass weed seeds with Group 1 and 2 herbicides. All the wild oats in the 155 fields surveyed for resistance turned out to be resistant to Group 1, and 82 per cent were resistant to both Groups 1 and 2.

Across all studied fields (over 700 across the province) that equated to 37 per cent of fields found with wild oats resistant to Group 1. Thirty per cent had Group 2 resistant wild oats, and 30 per cent had wild oats that were resistant to both.

Those doubly resistant populations were widespread across Manitoba’s regions. They were in the northwest and the southwest, scattered through central Manitoba and up into the Interlake.

The pattern is consistent across the region, said Charles Geddes, a national research scientist in weed ecology and cropping systems based in Lethbridge, and one of the names attached to the 2022 survey.

“We tend to see a similar story across the Prairies, where Group 1 resistance is by far the most abundant wild oat, and Group 2 resistance has been increasing, especially in recent decades,” he said.

Resistance rates climbing

The increase in Group 2 resistance stems from farmers switching herbicide modes of action when they discover Group 1 resistance, Geddes added.

“When many farmers find out that they have Group 1 resistance, they usually just switch over to relying on a Group 2, and that places greater selection pressure on that mode of action,” he said.

Adding to farmers’ concerns is emerging Group 15 resistance, which affects products like Avadex. The last assessment of Group 15 resistance across the Prairies, conducted between 2007 and 2009, found it in six per cent of surveyed fields.

Given increased reliance on these products due to Group 1 and 2 resistance, Geddes said it’s safe to assume that it has likely increased.

Wild oat weather

This year’s spring conditions may have contributed to a high level of weed escapes, including dry weather and windy days, Brown said. As such, some of those weeds might have dodged the spring burn off and many in-season applications.

“I think maybe a lot of weeds were not up yet … the sprays got put on, and then we started getting some rains in mid-summer,” she said.

Geddes agreed that weather conditions affect herbicide efficacy.

“In order for herbicides to have their intended activity on weeds in general, those weeds need to be actively growing,” he said. “The good news is that it also means there’s a greater likelihood that those survivors are susceptible, and not just those resistant.”

Farming with resistance

For farmers facing resistance issues, there are both proactive and reactive management strategies. One of these, Geddes said, is resistance testing.

“It’s one thing to assume that the population’s resistant because you had herbicide failure in the past, but resistance in wild oats can get complicated really quickly, and resistance testing kind of helps you understand what you’re dealing with,” he said.

With wild oats being primarily a self-seeding species, resistance patterns can vary significantly between neighbouring fields. Multiple resistance mechanisms can also create variable patterns of cross-resistance within herbicide groups.

“You may have resistance to, say, some Group 1 herbicides, but not others, and that means that there, you might still have some level of control from those remaining options,” Geddes said.

Management strategies hinge on reducing wild oat seeds returning to the ground. That could be a more diverse crop rotation, opening up more herbicide options, increasing seeding rates to boost crop competitiveness, or changing things up to include a winter annual or silage crop that is harvested early to disrupt the weeds’ lifecycle.

But most strategies on the list are for next year. Research suggests 60 to 70 per cent of wild oats seeds shatter from the plant and land on soil before spring wheat harvest, limiting the effectiveness of harvest weed seed control methods, Geddes said.

Fall is generally not the time to worry about wild oat control, since they’re annuals that have already set seed, Brown said.

“This is a time to evaluate and say, ‘okay, why did we have such an issue?’”

Wild oats present unique challenges

For non-chemical fall management of other weeds, Brown suggested tillage and potentially cover crops, depending on moisture conditions and the length of the fall growing season.

“Tillage, and the right kind of tillage at the right time, is … a really, really good tool,” she said.

The Manitoba resistance survey was last conducted in 2022, with the next survey planned for 2026, continuing on a five-year cycle to track the progression of resistance across the province, Geddes said.

The post Herbicide resistance thriving in Manitoba wild oats appeared first on Manitoba Co-operator.

“If I absolutely have to identify a weed and I don’t know what it is, I actually dig it up and I grow it out,” said Brown. “The minute you grow it out … a lot of the time it’s a lot easier to know when it’s a bigger plant.”

Grassy weeds are a particular identification challenge. They don’t have as many identifying features, compared to the cotyledons of broadleaf species —quite different from the true leaves —that often offer an easier point of reference.

If a weed can’t be fully identified in the moment, however, it often can be narrowed down to its weed family, which can lead to positive identification.

Brown, along with her Manitoba Agriculture colleague Dennis Lange, hosted a weed seedling identification seminar at the Ian N. Morrison Research Farm in Carman, Man., on May 21.

Seventy-two different weeds were on display at the seminar.

In terms of prominence across the province and farmer interest though, not all weeds are equal. Weeds such as green and yellow foxtail, redroot pigweed and wild buckwheat are perennial culprits in Manitoba.

“We’ve seen volunteer canola for a number of years now,” said Brown, “It’s a great crop but it’s also a really good weed.”

Brown admits that some weeds seem to respond more to weather patterns, particularly during dry cycles and increased salinity in soils.

“As we get into a wetter cycle, those salts that have come to the surface, they kind of get pushed back down again,” said Brown.

But when it comes to kochia, Brown says that particular weed is “a different beast.”

“In addition to it being a weed that loves salinity, we have an awful lot of herbicide resistance in it now,” she said.

The post VIDEO: What’s that weed seedling? appeared first on Manitoba Co-operator.

“One of the reasons why we’re struggling so much with herbicide resistance and some of the weeds that we’re trying to kill is that we have not had any new herbicides, or any new herbicide groups for a very long time,” she said earlier this spring.

WHY IT MATTERS: Weeds like kochia and waterhemp have been flagged for their ability to leave herbicide in the dust.

Some Group 4 herbicides have been in use since the Second World War, almost 80 years. Many individual herbicides have been developed over the intervening decades but the last new herbicide group to appear was in the mid-1980s. There have been some new families within Group 4 and Group 14 chemistries, she noted.

“Even if we have new products, they’re still killing weeds in the same way, because they’re still part of an existing group. The problem is that we don’t really have any new groups that kill weeds in a new way,” Brown said.

“If we start to get resistance to that group, it’s probably going to be resistant to a lot of products in the different families in that same group,” she added.

Last year, news broke that agri-chemical company FMC had submitted regulatory applications for an herbicide with a new mode of action, Group 28, in eight countries. It got the green light in Peru this April. That product registration, however, is targeted only for rice.

Developing resistance

Weeds do start with some resistance to an herbicide, even if it’s initially low enough that the weed dies.

“Over time, as we keep using that herbicide and, if it’s working really well, and it’s killing all the ones that aren’t resistant to it, then over time, the ones that are resistant are going to be the ones left behind,” Brown said.

When full blown herbicide resistance is seen in the field, the herbicide product will cease to work.

Brown said the only thing a farmer can do to prevent resistance is to try different methods of killing weeds and stretch out the time before the herbicide become ineffective.

She recommended farmers visit the Prairie Weed Monitoring Network website. The site houses weed survey results and resources for farmers and agronomists.

One tab details which weeds are resistant to which herbicides. There are many weeds, for example, developing resistance to Group 2 herbicides, while Group 4 resistance is rising in weeds like cleavers, wild mustard and kochia. Green foxtail has been showing resistance to Group 3 herbicides.

“We know we have some unconfirmed populations of (resistant) red root pigweed as well, and so we’ll be working on getting official confirmation of those,” she said.

“If you’ve been using a lot of Group 3s in the past, watch the red root pigweed. You may start to see some of those breakthroughs that Group 3s aren’t working very well anymore.”

Resistance can also come on quickly, Brown warned.

Monitoring weed resistance

The last weed survey was done across the Prairies in 2022 with the next one to be conducted in 2026. The surveys have been going on since the late 1970s.

“We basically do an abundance survey,” Brown said. “We rank our weed species by relative abundance, which is a combination of relative frequency within the field, relative uniformity within that field and density.”

Seven hundred fields are included in the survey. Last time, 155 were tested for resistance. The surveyors made sure surveyed fields included the top six crops in the province: canola, wheat, soybeans, oats, green corn and barley.

“We also did a few fields of peas, beans and sunflowers,” she said.

The number of herbicide resistant weeds have increased over the years of monitoring. The 2022 survey found that 75 per cent of fields surveyed had at least one herbicide resistant weed. That was up from 68 per cent in the survey before, which had much smaller coverage, Brown noted.

Based on a survey farmers filled out, herbicide resistant weeds were estimated to cost Manitoba farmers about $81 million in lost revenue or in added costs from using extra herbicides each year, she said.

Manitoba’s weed hit list

The top ten resistant weeds in Manitoba right now include green foxtail, buckwheat, volunteer canola, lambs quarters, red root pigweed, yellow foxtail and barnyard grass species.

Volunteer wheat, wild oats and round-leaved mallow had dropped in the previous survey, but this was due to wet springs and late seeding.

“If we have a normal year and more normal seeding times, I expect to see wild oats come back up in the ranking in the next weed survey,” she said.

Western advantage

Manitoba has always had more herbicide resistance than Saskatchewan and Alberta, Brown noted.

She recommended farmers keep a copy of the province’s Guide to Field Crop Protection handy. The document is available at all department service centres.

Brown also recommended farmers watch their labels. Some products are pre-seed and some are pre-emergence, meaning that producers can apply after seeding, but chemicals must be applied before the crop breaks ground. Farmers should make sure they are reading the labels on their herbicides and using them correctly, she said.

She also suggested websites including the Herbicide Resistance Action Committee. As well as resistance information, the website has details on cover crops, crop competition, harvest, weed seed control and integrated weed management. This website does not mention spraying, she warned, but focuses on other methods of controlling weeds.

Another recommended website was Weed Smart from Australia, which features farmer testimonials and weed control strategies.

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