Glyphosate-resistant Italian ryegrass ( <i>Lolium perenne ssp. multiflorum</i> ) control in preemergence and postemergence programs containing mixtures of residual herbicides

Abstract Glyphosate-resistant (GR) Italian ryegrass is one of the most troublesome weeds of rice in Mississippi. The most effective and economical management strategy to control GR Italian ryegrass is with preemergence (PRE) followed by postemergence (POST) herbicide programs. Two separate field studies were conducted in 2021–22 and 2022–23 in Stoneville, Mississippi, to evaluate GR Italian ryegrass control with fall-applied residual herbicide mixtures (Herbicide Mixture Study) and sequential PRE followed by POST herbicide programs with multiple applications of residual herbicides (Sequential Herbicide Application Study). In the Herbicide Mixture Study, dimethenamid-P, pyroxasulfone, and S -metolachlor alone provided ≥ 94% control of GR Italian ryegrass 21 d after treatment (DAT). The addition of flumioxazin to dimethenamid-P, pyroxasulfone, and S -metolachlor did not improve control 130 DAT. In the Sequential Herbicide Application Study, treatments with fall-applied dimethenamid-P performed better than those with acetochlor, except when fall-applied acetochlor was followed by a sequential application of clethodim plus S -metolachlor. Fall-applied residual herbicides are a necessary component of programs for control of GR Italian ryegrass in Mississippi.