Repeated Annual Applications of Herbicides for Control of Rhizome Johnsongrass (Sorghum halepense) in Cotton (Gossypium hirsutum)

Abstract

When postemergence applications of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were compared with DSMA (disodium salt of methylarsonic acid), MSMA (monosodium salt of methylarsonic acid), and glyphosate [N-(phosphonomethyl)glycine] for control of johnsongrass [Sorghum halepense(L.) Pers. # SORHA] in cotton (Gossypium hirsutumL. ‘Acala SJ-2′), repeated annual applications of sethoxydim were more successful than other herbicides in protecting yields of cotton and reducing populations of rhizome johnsongrass over time. After the first year of treatment with sethoxydim in 1982, when an 18% yield loss of cotton occurred, populations of rhizome johnsongrass were reduced to the extent that they were no longer a threat to yields in plots treated with sethoxydim in 1983 and 1984. Although DSMA and glyphosate improved yields when compared to cultivated control plots, substantial yield losses occurred every year, and populations of johnsongrass remained unchanged after 3 yr of treatment. Averaged over 3 yr, plots treated with sethoxydim produced 94% as much cotton as weed-free plots, compared to 60 and 45% for plots treated with glyphosate and DSMA/MSMA, respectively.