Adjuvants Affect the Efficacy of Glyphosate on Selected Perennial Weeds

Abstract The efficacy of glyphosate in controlling bermudagrass (BG) ( Cynodon dactylon L.), guineagrass (GG) ( Panicum maximum Jacq.), and purple nutsedge (PN) ( Cyperus rotundus L.) was determined when the herbicide was used alone or in combination with adjuvants: Frigate, LI-700, or VPG in a volume of 378 liters of water/ha. No loss of BG control was noted as the glyphosate level was lowered from 4.5 to 2.25 kg·ha -1 with Frigate added, but control decreased with VPG or no adjuvant addition (LI-700 not used). No reduction in control of PN was observed when glyphosate amount was lowered from 3.4 to 1.7 kg·ha -1 , provided LI-700 was present in the spray solution. With Frigate, VPG, or no adjuvant, however, the degree of PN control was less at 1.7 than 3.4 kg·ha -1 . Frigate, LI-700, and VPG were equally effective in improving glyphosate efficacy on GG when the herbicide was used at 3.4 kg·ha -1 , but the adjuvants had no effect at the herbicide level of 1.7 kg·ha -1 . Chemical names used: α-(p-alkyl phenyl) Ω-hydroxypoly (ethylenoxy) phosphate ester, propylene glycol (VPG); fatty amine ethoxylate (Frigate); isopropylamine salt of N -(phosphonomethyl) glycine (glyphosate); phosphatidylcholine methylacetic acid (LI-700).