Response of Bermudagrass (<i>Cynodon dactylon</i>), Quackgrass (<i>Agropyron repens</i>), and Wirestem Muhly (<i>Muhlenbergia frondosa</i>) to Postemergence Grass Herbicides

Abstract

Under greenhouse conditions, approximately 50% visible control of bermudagrass [ Cynodon dactylon (L.) Pers. ♯ 3 CYNDA], quackgrass [ Agropyron repens (L.) Beauv. ♯ AGRRE], and wirestem muhly ( Muhlenbergia frondosa L. ♯ MUHFR) was obtained using 0.56 kg/ha glyphosate [ N -(phosphonomethyl)glycine], CGA-82725 {2-propynyl-2-[4-([3,5-dichloro-2-pyridinyl] oxy) oxy)phenoxy propanoate}, 0.28 kg/ha fluazifop-butyl {(±)-butyl 2-[4-[(5-(trifluoromethyl)-2-pyridinyl)oxy] phenoxy] propanoate}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, and 0.11 kg/ha haloxyfop-methyl [methyl 2-(4-((3-chloro-5-(trifluoromethyl)-2-pyridinyl)oxy)phenoxy)propanoate]. Except for quackgrass, sethoxydim and fluazifop-butyl reduced shoot regrowth in plants clipped 3 to 6 h after treatment Sethoxydim required a 24-h duration on quackgrass foliage to reduce growth. Fresh weights of haloxyfop-methyl- and CGA-82725-treated plants required a 12- to 24-h clipping for reduced regrowth in all species. For all herbicides and species tested, little or no regrowth occurred when plants were clipped 48 h after treatment. A 1-h interval between split applications of sethoxydim and a 24-h interval between split applications of fluazifop-butyl and haloxyfop-methyl reduced fresh weights of bermudagrass regrowth when compared to an equivalent single rate. Regrowth of treated quackgrass indicated a 24-h interval was required for reductions with split applications of sethoxydim, fluazifop-butyl, and haloxyfop-methyl. Wirestem muhly regrowth was reduced after a 1-h interval between applications. In all species, superior control was obtained using two half-rate applications compared to one full-rate application.