Prairie cupgrass (Eriochloa contract) and windmillgrass (Chloris verticillata) response to glyphosate and acetyl-CoA carboxylase––inhibiting herbicides

A greenhouse experiment was conducted to determine the efficacy of glyphosate and acetyl-CoA carboxylase (ACCase)––inhibiting herbicides sethoxydim, clethodim, and quizalofop on prairie cupgrass and windmillgrass. Herbicides were applied at seedling, tillering, and heading growth stages. In addition, a study to determine glyphosate absorption and translocation in both species was conducted. Herbicide treatments were glyphosate at 541, 841, and 1121 g ha⁻⁻¹ and sethoxydim, clethodim, and quizalofop at 350, 210, and 70 g ha⁻⁻¹, respectively. In general, control of prairie cupgrass and windmillgrass increased as the rate of glyphosate increased. In addition, windmillgrass was less susceptible to glyphosate at heading and seedling stages than was prairie cupgrass. Efficacy of all ACCase-inhibiting herbicides applied at any growth stage was equal to or greater than efficacy of the highest rate of glyphosate applied at the same stage. Furthermore, all herbicide treatments were more phytotoxic to prairie cupgrass and windmillgrass at seedling stage than at tillering or heading. Differential response of prairie cupgrass and windmillgrass to glyphosate was attributed to differences in glyphosate translocation. Separate field experiments were conducted to evaluate preemergence (PRE) and postemergence (POST) herbicide treatments for prairie cupgrass and windmillgrass in no-till corn at Hays, KS, in 2001 and 2002. All PRE treatments provided at least 90%% control of windmillgrass in both years 6 wk after treatment (WAT). Prairie cupgrass was controlled effectively by acetochlor plus atrazine, alachlor plus atrazine, and S-metolachlor plus atrazine in 2001. In 2002, the only PRE treatments that gave 90%% control or greater of prairie cupgrass 6 WAT were alachlor plus atrazine and pendimethalin plus atrazine. Glyphosate sequential treatment was the only POST treatment that provided 100%% control of prairie cupgrass and windmillgrass in both years.Nomenclature: Acetochlor; alachlor; atrazine; clethodim; pendimethalin; quizalofop; sethoxydim; S-metolachlor; prairie cupgrass, Eriochloa contracta Hitchc. ERBCO; windmillgrass, Chloris verticillata Nutt. CHRVE; corn, Zea mays L.