Rapid on‐farm testing of resistance in lolium rigidum to key pre‐ and post‐emergence herbicides

Abstract

Overreliance on herbicides for weed control is conducive to the evolution of herbicide resistance. Lolium rigidum (annual ryegrass) is a species that is prone to evolve resistance to a wide range of herbicide modes of action. Rapid detection of herbicide‐resistant weed populations in the field can aid farmers to optimize the use of effective herbicides for their control. The feasibility and utility of a rapid 7‐d agar‐based assay to reliably detect L. rigidum resistant to key pre‐ and post-emergence herbicides including clethodim, glyphosate, pyroxasulfone and trifluralin were investigated in three phases: correlation with traditional pot‐based dose‐response assays, effect of seed dormancy, and stability of herbicides in agar. Easy‐to‐interpret results were obtained using non-dormant seeds from susceptible and resistant populations, and resistance was detected similarly as pot‐based assays. However, the test is not suitable for trifluralin because of instability in agar as measured over a 10‐d period, as well as freshly‐harvested seeds due to primary dormancy. This study demonstrates the utility of a portable and rapid assay that allows for on‐farm testing of clethodim, glyphosate, and pyroxasulfone resistance in L. rigidum, thereby aiding the identification and implementation of effective herbicide control options.