Target-Site Resistance to Glyphosate in Chloris Virgata Biotypes and Alternative Herbicide Options for its Control

Het Samir Desai,Bhagirath Singh Chauhan,Michael Thompson

doi:10.3390/agronomy10091266

Abstract

Due to the overdependence on glyphosate to manage weeds in fallow conditions, glyphosate resistance has developed in various biotypes of several grass weeds, including Chloris virgata Sw. The first case of glyphosate resistance in C. virgata was found in 2015 in Australia, and since then several cases have been confirmed in several biotypes across Australia. Pot studies were conducted with 10 biotypes of C. virgata to determine glyphosate resistance levels. The biotypes were identified as either susceptible, moderately resistant or highly resistant based on the glyphosate dose required to kill 50% of plants. Two glyphosate-susceptible (GS) and two glyphosate-resistant (GR) biotypes were identified by the dose-response study and analyzed for the presence of target-site mutation in the 5–enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. Performance of alternative herbicides to glyphosate as well as the double-knock herbicide approach was evaluated on the two GS (Ch and SGM2) and two GR (SGW2 and CP2) biotypes. Three herbicides, clethodim, haloxyfop and paraquat, were found to be effective (100% control) against all four biotypes when applied at the 4–5 leaf stage. All the sequential herbicide treatments, such as glyphosate followed by paraquat and glufosinate-ammonium followed by paraquat, provided 100% control of all four biotypes of C. virgata. This study identified effective herbicide options for the control of GR C. virgata and showed that target-site mutations were involved in the resistance of two biotypes to glyphosate (SGW2 and CP2). Results could aid farmers in selecting herbicides to manage C. virgata in their fields.

Highlights

Chloris virgata Sw. is a summer annual grass weed of the Poaceae family, commonly referred to by several other names such as feathertop Rhodes grass, feathered finger grass, oldland grass, feathered windmill grass, feathered Chloris and sweetgrass [1]
These results indicate that higher doses of glyphosate could control C. virgata; it is not economical and recommended to use higher doses of glyphosate because higher rates may enhance the risk of developing glyphosate resistance [14,16,17]
The results suggest that these herbicides are effective at controlling both GS and GR C. virgata plants when applied at this early growth stage; these herbicides may not provide successful control at later growth stages as the efficacy of herbicides tends to reduce when applied at later leaf stages in Echinochloa crus-galli (L.) Beauv., E. colona (L.) Link and Leptochloa chinensis (L.) [29]

Summary

Introduction

Chloris virgata Sw. is a summer annual grass weed of the Poaceae family, commonly referred to by several other names such as feathertop Rhodes grass, feathered finger grass, oldland grass, feathered windmill grass, feathered Chloris and sweetgrass [1]. This weed species exhibits a C4 photosynthesis mechanism [2], and has been identified as a host for aphids, barley yellow dwarf and cereal yellow dwarf viruses and some nematode species [1]. Due to high seed retention at crop maturity, C. virgata seeds could be captured through harvest weed seed control in sorghum [4]

Methods

Results

Conclusion