Herbicide strategies for reducing nutgrass (Cyperus rotundus L.) density in cotton (Gossypium hirsutum L.)

Abstract

Summary. A range of herbicides and combinations of herbicides were evaluated for controlling nutgrass (Cyperus rotundus L.) in 5 experiments in irrigated cotton in northern New South Wales. Control was assessed by comparing the density of tubers before and after treatment. Cotton lint yield and ginning percentage were also assessed. Combinations of herbicides, including 2,4-D, were evaluated in an additional experiment in fallow.

Multiple in-crop applications of glyphosate reduced tuber density by up to 96% over 2 seasons. This was improved with successive applications of glyphosate. Nutgrass tuber density was also reduced when glyphosate was combined with norflurazon (96%), benfuresate (92%), fluometuron (84%) or EPTC (87%). Similar reductions in nutgrass density were observed with methazole, dimethenamid, atrazine, and the combination of norflurazon + MSMA. Treatments which reduced nutgrass density generally resulted in average or above-average lint yields.

From these results, a strategy for controlling nutgrass in cotton can be developed using norflurazon preplanting, and multiple applications of glyphosate and/or MSMA in-crop.