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

Alysha T Torbiak,Randall N Brandt,Bill Hamman,Robert E Blackshaw,Charles M Geddes,Brian Beres

doi:10.1139/cjps-2020-0303

Abstract

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.

Highlights

Scott] is a troublesome, summer annual C4 tumbleweed that was introduced to North America as an ornamental garden forb in the late 1800s (Friesen et al 2009)
In western Canada, it is among the first weed species to emerge in the spring, but prolonged emergence periodicity can result in emergence after pre- or postemergence herbicide applications (Schwinghamer and Van Acker 2008; Dille et al 2017; Kumar et al 2018)
Kochia plants produce a large number of seeds, and these seeds can be dispersed over long distances when the stem of the senescing plant breaks at an abscission layer and the tumbleweed is blown by prevailing winds (Becker 1978; Stallings et al 1995; Friesen et al 2009; Beckie et al 2016)

Summary

Introduction

While the range of kochia in North America continues to expand northward, its current northern distribution is limited by growing season length and thermal time requirements for successful reproduction (Beckie et al 2012b). Despite these limitations, kochia remains the 15th most abundant weed species among annual crops in Alberta and Saskatchewan following post-emergence herbicide application, and the most abundant weed in the mixed grassland ecoregion of Alberta (Leeson 2016; Leeson et al 2019). Kochia plants produce a large number of seeds (up to 120 000 seeds·plant−1 in non-competitive environments), and these seeds can be dispersed over long distances when the stem of the senescing plant breaks at an abscission layer and the tumbleweed is blown by prevailing winds (Becker 1978; Stallings et al 1995; Friesen et al 2009; Beckie et al 2016)

Objectives

Methods

Results