Wheat School: Strategies for controlling herbicide resistant kochia


Kochia is one of the first weeds to emerge in spring. There are reports that 80 per cent of the kochia population emerges before anything else in a field.

The fact that it emerges so early puts a lot of pressure on the pre-emergent herbicide options out there.

In this Wheat School episode, Kara Oosterhuis is joined by Dr. Charles Geddes, weed research scientist at Agriculture and Agri-Food Canada’s Lethbridge location, to talk about herbicide resistant kochia surveys and research.

“A lot of our survey work now is showing that it’s more likely than not if you have kochia in the field it’s probably going to be glyphosate resistant,” says Geddes. It’s important to make sure to use other modes of action and to consider layering those modes of action with other pre-emerge or pre-plant products, says Geddes.

Surveying kochia resistance is done province by province, says Geddes, so the last survey for Alberta was done in 2017 and the next one is coming up this growing season. The survey showed that back in 2017, 50 per cent of kochia populations in Alberta were glyphosate resistant. (Story continues below video)

Group 2 resistant kochia has been around for quite a while — since the late 80s, all kochia populations in Western Canada are considered resistant to Group 2 herbicides.

“More recently, one of the emerging issues with kochia is auxinic herbicide resistant, or Group 4 herbicides,” says Geddes. Based on that 2017 survey, 18 per cent of kochia populations were resistant to dicamba, and some of the newer research is showing some resistance to fluroxypyr as well, mainly used for post-emergent situations.

In the hopes of preventing some of this resistance, it comes down to crop competition, says Geddes. Kochia can produce a large amount of seeds per plant, is quite plastic and adaptable. But part of that adaptation means sacrificing seed production. His recommendation implement management practices that increase plant competition. In the video, Geddes explains how row spacing and seeding rate will help create that competition.

Integrating optimal herbicide programs with diverse crop rotations is another focus of Geddes’ research. Kochia is also a summer annual, so it produces seed later in the growing season compared to other weeds, so one of the tools Geddes is looking at is using winter cereals into a crop rotation. The idea being that winter wheat, for example can compete and be harvested before kochia produces that viable seed.

Auxinic herbicide resistance, whether it’s cross- or multiple-resistance, is also on Geddes’ radar — figuring out whether the weed is resistant to dicamba, or fluroxypyr.

Geddes’ lab offers diagnostic testing to confirm potential resistance and has clear instructions on how to take a sample and where it should be sent.

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