New mode of action herbicides to combat herbicide resistant annual ryegrass (Lolium rigidum) in Australian cereal production

Herbicide resistance in annual ryegrass across southern Australia is currently a major issue for grain producers. Currently annual ryegrass (Lolium rigidum Gaudin) has evolved resistance to all post-emergent herbicides that can be used to control it in cereal crops and to the pre-emergent herbicide trifluralin. No new herbicide modes of action for the control of annual ryegrass have been marketed since the 1980s. In the past 5 years, research has been conducted with new mode of action herbicides that are selective in cereals. Prosulfocarb + S-metolachlor and pyroxasulfone effectively controlled 20 trifluralinresistant populations of annual ryegrass in pot trials. Field trials have determined that prosulfocarb + S-metolachlor, pyroxasulfone and dimethenamid-P could control trifluralin-resistant annual ryegrass when applied and incorporated by sowing (IBS) in the field. Prosulfocarb + S-metolachlor and pyroxasulfone were safe in barley, but dimethenamid-P caused unacceptable damage. Improved control of annual ryegrass was achieved by splitting the herbicide application between IBS and post-sow, pre-emergent (PSPE).