Understanding, mitigating, and managing PPO inhibitor (Group 14)-resistant kochia

Term: 5 years, beginning 2024
Status: Ongoing
Researcher(s): Charles Geddes, AAFC
SaskCanola Investment: $30,000
Total Project Cost: $619,000
Funding Partners: ADF, WGRF, SPG, SWDC, MCA, POGA

Objective

1.        Determine cross-resistance to PPO-inhibiting (Group 14) herbicides in PPO inhibitor-resistant kochia confirmed in SK.

2.        Determine cross- or multiple-resistance to other herbicide modes of action in PPO inhibitor (Group 14)- resistant kochia.

3.        Determine the mechanism conferring resistance to PPO-inhibiting (Group 14) herbicides in kochia.

4.        Continue monitoring kochia survey samples for PPO inhibitor (Group 14) resistance across the Canadian Prairies.

5.        Assess efficacy of alternative herbicides to manage multiple herbicide-resistant kochia prior to crop seeding.

6.        Determine the mid/long-term utility and sustainability of strategic tillage for kochia management.

7.        Assess the impact of timing and implement/depth of soil disturbance on kochia emergence, density, and the soil seedbank.

8.        Determine the mid/long-term impact of winter cereals and perennials in crop rotations on multiple herbicide-resistant kochia.

Project Description

Kochia has grown to be one of the worst agricultural weed problems on the southern Canadian Prairies where its impact on crop production has been exacerbated by warm dry summers over the past half decade. Kochia is a tumbleweed that thrives in conditions of drought, salinity, and heat stress, allowing it to compete with crops for essential resources, resulting in substantial crop yield losses. High genetic diversity combined with protogynous flowering result in rapid evolution and selection for resistance in response to herbicides followed by efficient transfer of herbicide resistance traits through pollen. Prolific seed production and tumbleweed seed dispersal also allow the plant to disperse seeds among multiple fields in a single year, further spreading resistant biotypes across farmlands.

Kochia on the Canadian Prairies can exhibit resistance to up to four herbicide modes of action, including Groups 2, 4, 9, and 14. Acetolactate synthase inhibitor (Group 2)-resistant kochia was documented first on the Canadian Prairies in 1988, and after about two decades, all kochia populations tested in this region were Group 2-resistant. Glyphosate (Group 9)-resistant kochia was confirmed in Canada in 2011, where it was found in chemical fallow fields located in southern Alberta. Recent surveys of Manitoba (2018), Saskatchewan (2019), and Alberta (2021) found glyphosate-resistant kochia in 59%, 87%, and 78% of the kochia populations tested, respectively. Synthetic auxin (Group 4)-resistant kochia was confirmed in Saskatchewan in 2015, and since spread to an estimated 1%, 45%, and 45% of kochia populations tested in Manitoba, Saskatchewan, and Alberta, respectively. However, we have documented variable overlap between fluroxypyr and dicamba resistance in kochia populations where a population may exhibit resistance to one, the other, or both of these auxin mimics.

Protoporphyrinogen oxidase (PPO) inhibitor (Group 14)-resistant kochia has been documented in a single kochia population from west-central Saskatchewan. Group 14 resistance in kochia drastically limits the herbicide options available to manage this weed using a preplant burndown before crop emergence. In response to wide-spread glyphosate resistance in kochia, many farmers switched to mixing a group 14 product (e.g., Heat, Aim, Authority, Valtera, etc. and the main kochia-active component of several others such as Fierce, Focus, Blackhawk, Goldwing, etc.) with glyphosate to regain efficacy of the pre-plant burndown treatment. However, if the kochia present were glyphosate-resistant, this resulted in widespread use of only a single herbicide mode of action for kochia control during this management window, and unfortunately substantial selection pressure for group 14 resistance. Very few herbicide options remain to control group 2, 4, 9, and 14-resistant kochia, and the ones that are available have rather limited use cases. For example, in canola, the only options left for control are Ethalfluralin, Bromoxynil, Bromoxynil + topramezone and Glufosinate. There is a need to understand which of the remaining herbicide options are available for kochia management, especially before crop planting, and also what approach can lead to better stewardship of these remaining active ingredients to mitigate further selection for resistance to new modes of action.