Johnsongrass (Sorghum halepense) Control in Soybeans (Glycine max) with Postemergence Grass Herbicides Applied Alone and in Mixtures

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Abstract
Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, CGA-82725 {2-propynyl 2-[4-[(3,5-dichloro-2-pyridinyl)oxy]phenoxy]propanoate}, RO 13-8895 {acetone-O-[D-2-[p-(α,α,α-trifluoro-p-tolyl)oxy]phenoxy]propionyl oxime}, and difenopenten {4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]-2-pentenoic acid} were evaluated as single and/or split applications for postemergence control of johnsongrass [Sorghum halepense(L.) Pers. ♯ SORHA] grown from rhizomes in soybeans [Glycine max(L.) Merr.]. Good to excellent control, crop safety, and yield enhancement were achieved with all herbicides evaluated. Antagonism between postemergence grass and broadleaf herbicides was evaluated by applying sethoxydim, CGA-82725, RO 13-8895, and difenopenten alone to soybeans infested with johnsongrass grown from seed, and applying these herbicides as mixtures with acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], or benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid). Acifluorfen was most antagonistic to the activity of postemergence grass herbicides, with difenopenten and sethoxydim the most susceptible to antagonism. Reductons in johnsongrass control were attributed to antagonism by broadleaf herbicides, which caused soybean yield reductions of up to 67%.