Triple-resistant” kochia — kochia resistant to herbicides in Groups 2, 4 and 9 — hasn’t yet been confirmed in Alberta despite recent media reports, says Hugh Beckie, a weed scientist with Agriculture and Agri-Food Canada.
Surveys have turned up two-way resistant kochia, specifically Group 2 plus Group 4, and Group 2 plus Group 9 resistant weeds, but so far no populations have been confirmed that combine resistance to all three chemistry classes.
“I expect it’s out there already, but it hasn’t been confirmed,” he says. All populations of kochia are Group 2 resistant. According to Beckie, the most recent weed surveys showed that five per cent of kochia populations were Group 9 or glyphosate resistant.
“It’s only a matter of time until we get populations with all three types of resistance because of kochia’s extensive seed movement,” he says.
“The key message is that if it’s an imminent threat, carefully plan your crop rotations and make sure you have the appropriate herbicides available to control kochia.”
In wheat, the only herbicide mode of action remaining to producers for kochia control is Group 6, so producers should think carefully about their plan of attack. “We already have Group 2 kochia, could have Group 9 kochia, and if you’ve used a lot of Group 4 in the past and you’re planting wheat on wheat on wheat, you have to be prepared to move out of wheat for a while and diversify to other crops where resistant kochia may be controlled,” he says.
Those crops can’t be pulses, though, as pulses rely on Group 2 chemistries. Roundup Ready or Liberty Link canola systems are an option.
In the southern Prairies, Beckie says producers are quite concerned about the problem. “If their populations become resistant to Group 4, it would have a big impact on their bottom line.”
Story “different” in Manitoba
Jeannette Gaultier, a weed scientist with Manitoba Agriculture, says random tests have found about 15 per cent incidence of glyphosate-resistant kochia in Alberta and Saskatchewan, but the story is “quite different” in Manitoba.
“We’ve found most of our glyphosate-resistant kochia in the Red River Valley area, in glyphosate-tolerant soybean and corn,” she says. “Our incidence is about five per cent.” Less chemfallow in Manitoba accounts for the difference.
In Manitoba, the Manitoba Canola Growers Association and Manitoba government have joined forces with the Pest Surveillance Initiative (PSI), a “grower-led molecular detection laboratory that identifies, quantifies and tracks risks to successful crop production.”
The lab uses polymerase chain reaction (PCR) tests to assess samples. Farmers can even submit green material without having to wait for plants to set seed, she says.
Gaultier’s team just released an up-to-date map on the PSI website (online at mbpestlab.ca), based on last year’s lab results, showing areas affected by resistant populations of kochia. Five rural municipalities are affected, she says. Producers can check the map to determine whether a plan is needed on their operations.
Gaultier says it’s “hard to know” whether the problem is getting better or worse. Many producers are aware of the problem and have begun tank mixing or applying different modes of action.
Prairie producers have also started using pre-emergence products, such as those in Groups 14 and 15. Some Group 3 and Group 8 products can be used as pre-seed burnoff to tackle herbicide resistant weeds, followed by a post-emergent application of glyphosate. Pre-emergent herbicides that specifically target kochia include Edge (Group 3) and Authority (Group 14), says Gaultier.
Though cereal crops are fairly competitive against kochia, cereal producers should stay on top of the situation early. “It’s important for producers to target their main weed problems,” she says. “If kochia is the one you’re really concerned about, pick something with multiple modes of action, and again you’ve got a competitive crop in wheat so get it in there as early as you can, and keep seeding rates up.”