Influence of herbicide combinations and application technology on cogongrass (Imperata cylindrica) control

Field experiments were conducted to evaluate various herbicides and application technologies for the control of cogongrass. Imazapyr at 0.8 kg ae/ha provided the highest cogongrass control, followed by glyphosate (3.4 kg ae/ha) and sulfometuron (1.1 kg ai/ha) when applied as a single application. When sequential applications were evaluated, glyphosate plus imazapyr provided the best control. Sulfometuron could be applied sequentially after imazapyr or glyphosate with no loss of control, but control was less if sulfometuron was the initial herbicide. Tank mix combinations of glyphosate and imazapyr (100% rate al 3.4 and 1.1 kg ae/ha, and subsequent rates of 0 + 100, 25 + 75, 50 + 50, 75 + 25, and 100 + 0% of each herbicide, respectively) provided similar cogongrass control regardless of rate. Control using imazapyr improved from 20 to 40% with 234 L/ha diluent volume when compared to 46 L/ha. Glyphosate at either of these volumes provided from 0 to 21% inhibition of cogongrass. A 50% concentration of imazapyr applied twice with a ropewick provided greater control than a 33% concentration with one pass or either concentration of glyphosate with one or two passes. Efficacy with glyphosate applied using a ropewick was not affected by concentration or number of passes.