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

Abstract

Kochia [<i>Bassia scoparia</i> (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 (<i>Triticum aestivum</i> 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 2013-2015. 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.

Fluroxypyr-resistant kochia [Bassia scoparia (L.) A.J. Scott] confirmed in Alberta

“…Limited alternative herbicide options to control auxinic herbicide-resistant kochia postemergence in cereal crops (Beckie et al 2019;Torbiak et al 2021b) indicates that further selection pressure is inevitable due the broad land base planted to cereals in western Canada. To alleviate further selection for these biotypes, farmers are advised to implement alternative chemical and non-chemical weed control practices.…”

“…Auxinic herbicide-resistant kochia in Alberta will limit herbicide options for control of these biotypes in cereal crops, like wheat, and also other uses like chemical fallow (Beckie et al 2019;Torbiak et al 2021aTorbiak et al , 2021b. There is a need to understand whether auxinic herbicideresistant kochia populations in Alberta are resistant to dicamba only, or also to other synthetic auxins.…”

Burial Environment Drives Seed Mortality of Kochia (Bassia scoparia), Wild Oat (Avena fatua), and Volunteer Canola (Brassica napus) Irrespective of Crop Species

“…The entire experiment was repeated in seven different burial environments consisting of different soils and environmental conditions (Tables 1 and 2). The three factors were crop species (3), weed seed species (3), and burial environment (7). Within each burial environment, the main plot factor consisted of crop species (wheat, canola, and field pea), whereas the split plot factor consisted of weed seed species (kochia, wild oat, and volunteer canola).…”

“…Resistance to multiple herbicide sites-of-action exacerbates the impact of kochia, wild oat, and volunteer canola on Canadian farms by limiting the herbicide options available for their management [ 5 , 6 , 7 ]. In the Canadian prairies, resistance to 3, 4, and 3 herbicide sites-of-action have been documented in kochia, wild oat, and volunteer canola, respectively [ 8 ].…”

Wheat Density Alters but Does Not Repress the Expression of a Fluroxypyr-Resistant Kochia (Bassia scoparia) Phenotype

“…Resistance to multiple herbicide sites-of-action in kochia limits options for herbicidal control [3,14,15], creating a need for integrated weed management programs that exploit non-chemical weed control strategies. Cultural management tools used to increase crop competitive ability can interact with and augment herbicide efficacy [16][17][18][19].…”