Kochia is becoming more of an issue for farmers as it continues to build herbicide resistance.
Dr. Charles Geddes is a Research Scientist in Weed Ecology and Cropping Systems with Agriculture and Agri-Food Canada - Lethbridge.
He says it's now safe to assume all kochia is Group 2 resistant, with Glyphosate resistance (Group 9) building as well.
"For glyphosate resistance on the Canadian Prairies, it was first discovered in 2011 in southern Alberta. A survey the subsequent year found 4 per cent of the kochia populations tested were glyphosate-resistant. That increased from 4 per cent to 50 per cent after five years. So, in 2017, 50 per cent were glyphosate-resistant, and now more recently we repeated that survey, in 2021 showing 78 per cent more glyphosate-resistant. For Saskatchewan, glyphosate resistance although there were confirmations in farmer samples in 2012, the survey in 2013, found about 5 per cent of the populations were glyphosate resistant. That survey was just was repeated in 2019, and the results haven't officially been released yet, but we're seeing similar levels to Alberta. In Manitoba, we found glyphosate resistance in 2013 in less than 1 per cent of the population, which increased to 58 per cent by 2018. "
He says if you're developing a management strategy dealing with kochia on the prairies, it's safe to assume that you're dealing with a glyphosate-resistant weed.
Kochia resistance is also showing up in Group 4 - Synthetic Auxins which is used to manage kochia in small grain cereal crops.
Geddes says they've also confirmed Synthetic Auxins' resistance in Kochia in all three prairie provinces.
A 2021 survey in Alberta found 44 per cent of the population had some level of Fluroxypyr resistance, and 28 per cent of the population had some level of Dicamba resistance.
With herbicide resistance building he says a herbicide-only weed management program is not enough when it comes to Kochia.
"A lot of our research has been focusing on a cropping systems perspective. Where we're looking at managing kochia throughout crop rotations, with some crops being more competitive with kochia than others. We're finding that effective strategies are ways to optimize your crop spatial arrangement within the field. What I mean by that is reducing row spacing. Increasing seeding rates help to make your crop more competitive and reduce the kochia throughout the rotation. So that's been a very effective strategy for us in our Lethbridge study. Offering up to 80 per cent control of kochia by decreasing row spacings, and increasing seeding rates throughout the rotation. When it comes to crop rotation, we're finding that adding in alternative crop lifecycles like winter wheat into the rotation is an effective strategy to reduce kochia populations, because the crop is established in the spring. It's quite competitive with kochia, and it's harvested before kochia produces viable seed typically."
The Weed Ecology and Cropping Systems research program at Agriculture and Agri-Food Canada Lethbridge offers a free testing service to confirm glyphosate (Group 9) or auxinic (Group 4) herbicide resistance in kochia.
If you suspect resistance in kochia to either of these herbicide modes of action you can email Charles.Geddes@canada.ca