Herbicide strategies for managing glyphosate-resistant and-susceptible kochia (Bassia scoparia) in spring wheat


Torbiak, A.T., Blackshaw, R.E., Brandt, R.N., Hamman, B., Geddes, C.M. (2021). Herbicide strategies for managing glyphosate-resistant and-susceptible kochia (Bassia scoparia) in spring wheat. Canadian Journal of Plant Science, [online] 101(4), 607-621. http://dx.doi.org/10.1139/cjps-2020-0303

Plain language summary

Farmers in the Great Plains region rely on the herbicide glyphosate (group 9) for broad-spectrum and cost effective weed control before planting annual crops in no-tillage or reduced-tillage systems. Over the past decade, kochia biotypes with resistance to glyphosate have increased in abundance, resulting in poor weed control and significant crop yield losses. Researchers from the Agriculture and Agri-Food Canada Lethbridge Research and Development Centre along with Hamman Ag Research Inc. have identified herbicides for use before planting wheat or within the wheat crop that are effective for managing glyphosate-resistant and susceptible kochia biotypes. Due to the recent discovery of kochia biotypes with resistance to group 4 herbicides, wheat farmers may benefit from the excellent kochia control provided by alternative herbicide modes of action like group 14 herbicides (e.g., sulfentrazone) applied before wheat emergence, or group 6 (e.g., bromoxynil) or 27 (e.g., pyrasulfotole) applied within the wheat crop. Use of herbicides with alternative modes of action in mixture or rotation will help reduce the selection pressure for herbicide-resistant kochia biotypes in the Great Plains region.


Kochia [Bassia scoparia (L.) A.J. Scott] is a summer annual tumbleweed that is tolerant of heat, drought, and salinity and capable of causing large yield losses in spring wheat (Triticum aestivum L). Increased incidence of glyphosate-and acetolactate synthase (ALS) inhibitor-resistant kochia in western Canada warrants investigation of alternative herbicides to manage these biotypes. Herbicides applied pre-or post-emergence in spring wheat were evaluated based on crop tolerance and control of ALS inhibitor-resistant kochia accessions with and without the glyphosate resistance trait in five environments near Lethbridge and Coalhurst, Alberta, from 2013 to 2015. The most effective and consistent treatments for kochia management included sulfentrazone applied pre-emergence and fluroxypyr/bromoxynil/2,4-D or pyrasulfotole/bromoxynil applied post-emergence. All of these treatments resulted in ≥90% visible control in all environments and ≥90% kochia biomass reduction compared with the untreated control in Lethbridge 2014 and 2015. MCPA/dichlorprop-p/mecoprop-p, dicamba/2,4-D/mecoprop-p, and dicamba/fluroxypyr resulted in acceptable control among environments (≥80% visible control in all environments and ≥80% kochia biomass reduction in Lethbridge 2014 and 2015); however, the latter two options caused unacceptable (>10%) wheat visible injury in Coalhurst 2014. Recent confirmations of auxinic herbicide-resistant kochia in western Canada—due, in part, to use of synthetic auxins to manage glyphosate-resistant kochia in small-grain cereals—will limit kochia management options. When implemented with non-chemical tools as part of an integrated weed management program, alternative herbicide modes of action like protoporphyrinogen oxidase inhibitors before and photosystem II or 4-hydroxyphenylpyruvate dioxygenase inhibitor(s) within spring wheat could mitigate selection for multiple herbicide-resistant kochia.

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