RESIDUE REMOVAL METHOD AND HERBICIDES FOR TALL FESCUE SEED PRODUCTION.1. WEED-CONTROL

Pacific Northwest grass seed production is in transition from reliance on open-field burning to new systems integrating chemical weed contro l with mechanical removal of crop residues. Field tests were initiated in 1989 to ascertain if these systems can meet seed trade expectation s for genetic purity while maintaining normal seed yields. Fourteen he rbicide treatment sequences plus an untreated check were evaluated und er five residue removal methods at two sites during two consecutive gr owing seasons. Residue removal included two methods of burning and thr ee nonburn systems varying in thoroughness of removal. Acceptable cont rol (>90% reduction in ground cover) of volunteer seedling tall fescue (Festuca arundinacea Schreb.), the most abundant weed in all tests, w as achieved by nearly all herbicide treatments at one site. At the oth er site, however, thorough residue removal or aggressive herbicide tre atments were required to achieve this same degree of control. Over sit es and pars, acceptable control without use of herbicides was achieved in one case out of four for the most thorough mechanical residue remo val system (vacuum-sweep, VS) and twice by open-field burning (FB). Pr eemergence (PRE) application of pendimethalin -ethylpropyl)-3,4-dimeth yl-2,6-dinitrobenzenamine] provided acceptable control following VS, F B, and propane flaming (PP). Oxyfluorfen -ethoxy-4-nitrophenoxy)-4-(tr ifluoromethyl)benzene applied postemergence (POST) at 0.28 kg a.i. ha( -1) plus diuron [N'- (3,4-dichlorophenyl)-N,N-dimethylurea] at 2.7 kg a.i. ha(-1) controlled weeds in all residue removal methods at one sit e, and for VS, FB, and PP at the other site. Applied in sequence after each of four PRE herbicides, POST application of 0.14 kg ha(-1) oxyfl uorfen plus 1.8 kg ha(-1) diuron controlled volunteer seedling tall fe scue better than POST application of 2.7 kg ha(-1) diuron without oxyf luorfen. With properly chosen herbicide treatments, seed trade standar ds for tall fescue can be met without field burning.