Farmers never really stood a chance against kochia this year.
First, it was a dry year following a dry year, and kochia thrives in dry conditions.
Then those dry conditions drew salts in the soil toward the surface — and kochia loves saline soils.
And finally, those saline soils delayed emergence in kochia, so any herbicide application likely hit at the wrong time to make a difference.
All in all, it was a perfect storm and one that will have lingering after-effects in the years to come.
“Across Western Canada, we’re seeing kochia being very abundant compared to other years,” said federal research scientist Charles Geddes. “It’s more of a problem this year than it was in previous years.”
If that weren’t bad enough, herbicide resistance is also on the rise in kochia, which can outcompete other crops at the best of times (and even better in bad ones). It started developing Group 2 herbicide resistance in the late 1980s, and today, all kochia populations are considered resistant to that herbicide group.
Part of that rapid spike can be attributed to the weed’s biology. Populations are genetically diverse, so plants evolve quickly to selection pressure. And resistant plants can share their genes relatively easily with non-resistant ones up to 100 metres away — a trait made worse because its stems break in the fall, creating tumbleweeds that deposit seeds up to one kilometre away as they go.
That’s what has made it Western Canada’s most abundant and economically devastating weed species, said a provincial crop specialist.
“It can produce up to 25,000 seeds, and then at the end of the growing season, the stem breaks off at the soil surface and it starts to tumble,” said Neil Whatley.
“They’ll tumble this fall with the wind and that’s where you get the seed dispersal.”
As a result, glyphosate (Group 9) resistance in southern Alberta kochia populations has increased from about five per cent in 2012 to 50 per cent in 2017. That number is expected to be even higher in 2018 once testing is complete this winter.
This may also be the year that triple-resistant kochia — resistant to Groups 2, 4, and 9 — is confirmed in Alberta, said Geddes.
“We have several suspected cases, but to date, none of those have been confirmed,” he said. “But I’m fairly confident that we’ll have that showing up in this year’s test.”
Managing the weed
That’s why it’s vital to get ahead of the weed post-harvest and before next year’s seeding, said Whatley.
“The risk is that the plants will blow and disperse more seeds over more acres, so it’s important to control this weed before it goes to seed if you can,” he said.
“It doesn’t have much dormancy, so if you can prevent those escapes from getting away on you, that can help control it.”
One of the best ways is to mow the kochia plants this fall so they don’t have an opportunity to turn into tumbleweeds. But it’s important to time any mowing for after the plant has transferred into its reproductive stages. If the plants are mowed while they’re still in their vegetative stages, they’re more likely to regrow.
Post-harvest herbicide application may have some value, but the science is still out on that.
“You’re essentially managing the plants after their seed production is already done, so those seeds could still remain viable,” said Geddes, who is currently working on a study on optimal timing for both pre- and post-harvest herbicide applications.
“Right now, we don’t necessarily know if it’s beneficial or not.”
Site-specific tillage could also help, Geddes added.
“We know that kochia populations tend to be more abundant in zero-tillage production systems,” he said, adding its seed viability is only one to two years.
“Tilling some of the problematic patches could be a beneficial tool as well to try and decrease some kochia populations.”
Next spring, start with a solid crop rotation to help rotate herbicide groups, seed early, and only plant clean seed.
“It’s always good to use clean seed,” said Whatley. “If you’re going through some kochia at harvest time with the combine, it’s good to get your seed cleaned.”
And for this weed, timing is everything in herbicide application.
“Kochia grows rather rapidly, and often by the time we’re applying our post-emergent herbicide, it’s actually outgrown the stages where it’s best managed,” said Geddes. “If kochia reaches some later stages of vegetative growth, it gets to be much more difficult to manage with a herbicide.”
If you suspect there’s herbicide-resistant kochia in your field, don’t wait until spring to get those plants tested. Fall is actually the best time of year to get it done, through the free federal screening program.
“With our survey, what we’re recommending growers do is collect those samples in October,” said Geddes.
The program requires viable seeds, so the best bet is to leave a couple of plants growing in the field and then collect the seeds after harvest to send them in for testing. “If they wait until after harvest, there will likely be a greater proportion of the seeds that would be viable.”
That testing will give producers the information they need in order to manage kochia better next year, he added.
“It’s going to be very important to get out there and scout fields — not just the area of the field where you would expect your crop to thrive, but also some of these low-lying areas where kochia will likely be present,” he said. “It’s important to stay ahead of kochia to manage it.”
To request a screening, contact Charles Geddes at [email protected] or 403-359-6967.