PERFORMANCE OF POSTEMERGENCE HERBICIDES ON EIGHT NATIVE GRASS SPECIES GROWN FOR SEED IN CENTRAL OREGON, 2000-2002
Herbicide screenings were conducted over two seasons on eight native grass species: great basin wildrye, bluebunch wheatgrass, streambank wheatgrass, big bluegrass, Idaho fescue, Indian ricegrass, squirreltail and prairie Junegrass. Fall applications were made 18 October 2000 and 14 October 2001. These included 1x and 2x label rates of dicamba, dimethenamid, diuron, flufenacet + metribuzin, metribuzin, oryzalin, oxyfluorfen, primisulfuron, pronamide, sulfosulfuron, and terbacil. Treatments were applied to the same plots two years in a row to increase confidence related to crop safety. During 2002 treatments producing the most negative effect were 2x rates of terbacil at 1346 g ha-1 and pronamide at 458 g ha-1. Treatments with the least effect on both stand reduction and reduced heading across grass species were 1x rates of diuron at 1614 g ha-1, oxyfluorfen at 175 g ha-1 and metribuzin at 336 g ha-1. Stand reduction across herbicide treatments was least for great basin wildrye, and was greatest for prairie Junegrass and squirreltail. The least herbicide impact on heading was observed with great basin wildrye and streambank wheatgrass, while it was most severe for squirreltail and prairie Junegrass.