There’s an easy way to tell if you have glyphosate-resistant kochia in your field — flip a coin.
“Half the fields that have kochia in them now have resistant populations,” said federal research scientist Charles Geddes.
Five years ago, only five per cent of kochia populations in Alberta fields were resistant to glyphosate (the active ingredient in a wide range of products marketed as Group 9 herbicides). The number shot up to 50 per cent in 2017, according to a post-harvest survey of more than 300 sites with kochia populations in southern Alberta.
That’s no surprise, given how quickly kochia has overcome herbicide modes of action in the past, said Geddes. Kochia started developing Group 2 herbicide resistance in the late 1980s, and today, all kochia populations are considered to be Group 2 resistant.
“Fifty per cent of populations really isn’t that far off the mark as far as how quickly glyphosate resistance is spreading across the Prairies,” said Geddes.
Part of that rapid spike can be attributed to kochia’s biology. There is a lot of genetic diversity in kochia populations, and that allows the weeds to evolve quickly to selection pressure. Moreover, resistant plants can share their genes relatively easily with non-resistant plants up to 100 metres away.
Then there’s the ‘tumbleweed mechanism.’ In the fall, the plant stems break off and then blow across the countryside, depositing resistant seeds up to one kilometre away.
But an overreliance on glyphosate is “at the centre of the issue,” said Geddes. Right now, producers can use glyphosate at multiple times during the growing season, both pre- and post-harvest as well as after emergence.
“And why wouldn’t they? It’s a rather inexpensive broad-spectrum herbicide that offers very good control of most weeds,” said Geddes. “But whichever weed management tool we seem to be focusing on, we start seeing resistance to that tool rather rapidly in kochia populations.”
That’s also led to the rise of triple-resistant kochia populations, which are resistant to groups 2, 4, and 9.
“I wouldn’t be surprised if we’re now starting to see resistance to auxinic, or Group 4, herbicides expanding in Western Canada as well,” said Geddes. “But a triple-resistant kochia biotype would significantly limit our herbicide options as far as control of kochia.”
These triple-resistant populations, which showed up last year in Alberta and Saskatchewan, could force growers to shift toward Group 6 products. However, that will likely just be another stop-gap solution, said Geddes.
“There could be a day where we don’t really have many options to manage kochia using herbicides,” he said. “So what we want to see now is trying to mitigate further selection for herbicide resistance.”
Producers will need to start rotating their herbicide modes of action and using non-chemical tools if they hope to manage the few remaining modes of action available for kochia control, he said.
One such tool is seeding timing. In comparing glyphosate-resistant kochia to susceptible plants, the resistant plants tend to emerge later in the growing season, and that could be used to farmers’ advantage.
Producers could either delay seeding and use their pre-seed burn-down to manage resistant kochia populations prior to seeding, or they could seed very early to promote a crop that could outcompete the weeds.
“Because we have a difference between our resistant and susceptible populations, we can start trying to adapt our management strategies based on timing of emergence within the field.”
Since kochia seed banks in the soil only last one to two years, producers could also use tillage to ‘spot manage’ resistant kochia populations.
“Tillage could be an effective tool. It does have its place if used sparingly and only when needed for spot management.”
But knowledge is the greatest weapon that farmers have against this threat. A coin flip won’t really tell you if the kochia in your field is resistant to glyphosate or other herbicides, but a free federal screening program can.
“We want to help farmers determine whether they have resistant populations or not and what options are left once they do start seeing some resistance,” said Geddes, who is leading the screening program.
Farmers who suspect they have resistant populations in their fields can request a free, confidential screening for both Group 4- and Group 9-resistant kochia.
To request a screening, contact Geddes at firstname.lastname@example.org or 403-359-6967.