Tolerance of Red Fescue (Festuca rubra) and Bentgrass (Agrostisspp.) to Sethoxydim

Abstract

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} is used to control weedy grasses in red fescue (Festuca rubraL. # FESRU andF. rubrassp.commutata), an important seed crop in Oregon. The sethoxydim rate required to reduce growth rate of 11 cultivars of red fescue and four cultivars of bentgrass (Agrostis tenuisSibth. # AGSTE andA. stoloniferaL. var.palustris# AGSST), a common contaminant in red fescue fields, by 50% (GR50) was determined in greenhouse and laboratory experiments. Field experiments compared only red fescue cv. ‘Pennlawn’ and bentgrass cv. ‘Penncross'. The GR50values for Pennlawn red fescue in the field, the greenhouse, and the laboratory were 30 kg ai/ha, 15 kg/ha, and 5300 μM, respectively. Penncross bentgrass was approximately 400, 1400, and 12 900 times more susceptible than Pennlawn red fescue in the field, in the greenhouse, and in laboratory experiments, respectively. Plants were at different growth stages in the different experiments. The xylene and surfactant used as a solvent for the technical grade sethoxydim was as toxic to red fescue without sethoxydim as when sethoxydim was included. Cultivars of red fescue differed in their response to sethoxydim, but cultivars of bentgrass did not. The GR50's of other species tested in the greenhouse were >4 kg/ha for annual bluegrass (Poa annuaL. # POAAN), 0.22 kg/ha for tall fescue (F. arundinaceaSchreb. # FESAR), 0.37 kg/ha for downy brome (Bromus tectorumL. # BROTE), and 0.017 kg/ha for Italian ryegrass (Lolium multiflorumLam. # LOLMU).