Weed Control from Herbicide Combinations with Three Formulations of Glyphosate¹

Abstract

Greenhouse studies were conducted to evaluate weed control from various formulations of glyphosate alone and in combination with postemergence herbicides. Tank mixtures did not increase barnyardgrass control 2 wk after treatment (WAT) when compared with glyphosate alone; however, tank mixtures did reduce barnyardgrass fresh weight 4 WAT when compared with glyphosate alone in several instances. Antagonism was observed when chlorimuron was combined with all formulations of glyphosate 4 WAT, but control was not reduced when compared with glyphosate alone. Selective herbicides added to glyphosate had an additive or antagonistic effect on prickly sida fresh-weight reductions. Antagonism of pitted morningglory fresh-weight reductions occurred when glyphosate was combined with all herbicides except acifluorfen, which had an additive effect. Fomesafen or lactofen effectively controlled hemp sesbania 2 WAT without the addition of glyphosate. Acifluorfen and chlorimuron combined with glyphosate Cheminova, Monsanto, or Zeneca reduced hemp sesbania fresh weight nearly twofold more than glyphosate alone.Nomenclature: Acifluorfen; chlorimuron; fomesafen; glyphosate; lactofen; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A. W. Hill # SEBEX; pitted morningglory, Ipomea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP.Additional index words: Additive effects, antagonism, reduced rates, synergism.Abbreviations: ALS, acetolactase synthase; C, Cheminova; LSD, least significance difference; M, Monsanto; POST, postemergence; WAT, weeks after treatment; Z, Zeneca.