Multiple resistance in goosegrass to clethodim, haloxyfop-methyl and glyphosate

Abstract

Background: Goosegrass is one of the most troublesome weed species in Brazil due to its wide dispersion and the ability to evolve herbicide resistance. Objective: Investigate the response of goosegrass accessions from Mato Grosso, Brazil to glyphosate, clethodim, and haloxyfop. Methods: Goosegrass seed samples were collected from seventeen production fields (accessions) in Mato Grosso and screened with the recommended label rates of clethodim, haloxyfop-methyl, and glyphosate. Six accessions withstood the label rate of the evaluated herbicides and were subjected to a dose-response study. Out of the six accessions, two were selected for further F1 dose-response investigations due to their ability to survive the label rate of the three herbicides individually. All studies were conducted under greenhouse conditions in a completely randomized design with four replications, and the F1 dose-response study was replicated in time. Results: All six accessions investigated in the dose-response study presented ED50 values higher than susceptible plants for control and biomass reduction. Haloxyfop-methyl had the highest resistance ratios, followed by clethodim and glyphosate. The two accessions investigated in the F1 dose-response study were confirmed to be cross-resistant to clethodim and haloxyfop-methyl and showed low-level resistance to glyphosate. Conclusions: The continuous reliance of POST herbicides for weed management in Mato Grosso cropping systems has selected goosegrass accessions that can withstand high rates of ACCase-inhibiting herbicides, particularly haloxyfop-methyl. Moreover, two accessions with resistance to ACCase-inhibiting herbicides, clethodim and haloxyfop-methyl, and low-level resistance to glyphosate were identified, suggesting the presence of multiple resistance in goosegrass accessions from Mato Grosso, Brazil.