NUTGRASS (CYPERUS-ROTUNDUS L) CONTROL IN COTTON (GOSSYPIUM-HIRSUTUM L)

The effects on cotton lint yield and nutgrass tuber density of 12 treatment combinations were examined. Treatments included preplant norflurazon and benfuresate, in-crop cultivation, glyphosate and MSMA, and post-harvest glyphosate. The effects on tuber density of a further 14 treatment combinations of cultivation, MSMA, glyphosate, and norflurazon were examined in fallow. Under a traditional nutgrass control program of in-cotton cultivation and MSMA, nutgrass tuber density (no./m(2)) increased from 216 (0-0.15 m soil core) in 1990 to 1112 in 1992, with an average cotton yield of 1239 kg lint/ha. This result compared well with the untreated control, where the tuber density increased to 1641 tubers/m(2) in 1992, with an average lint yield of 959 kg/ha. The best treatment was a combination of norflurazon, benfuresate, glyphosate, and cultivation, resulting in a tuber density of 220 tubers/m(2) in 1992 and an average lint yield of 1217 kg/ha. Repeated applications of glyphosate in fallow effectively controlled nutgrass, with incremental improvements in control from additional glyphosate applications. Monthly glyphosate applications reduced the tuber density from 334 tubers/m(2) in 1990 to 47 in 1992 at one site, and from 334 tubers/m(2) in 1990 to 50 in 1992 on a second site. Overall, the results showed that traditional nutgrass control techniques were unsatisfactory, but repeated glyphosate applications gave effective nutgrass control both in cotton and in fallow.