INFLUENCE OF RESIDUE REMOVAL METHOD AND HERBICIDES ON PERENNIAL RYEGRASS SEED PRODUCTION .1. WEED-CONTROL

Grass seed production in the Pacific Northwest is in transition from r eliance on open-field burning to systems integrating mechanical remova l of postharvest crop residues with chemical weed control. Field tests of the ability of these systems to meet current seed certification st andards while maintaining normal seed yields were initiated in 1989. F ourteen herbicide treatment sequences plus an untreated check were eva luated under five residue removal systems at two sites during two cons ecutive growing seasons. Residue removal methods were three non-burn s ystems varying in thoroughness of residue removal and two methods of b urning. Among the nonburn systems, adequate control of volunteer peren nial ryegrass (Lolium perenne L.), the most abundant weed in all tests , was most readily achieved in plots where residue was most thoroughly removed. Herbicide treatments providing the best weed control in both years at both sites included preemergence (PRE) metolachlor -ethyl-6- methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] followed by poste mergence (POST) oxyfluorfen ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] plus diuron [N'-(3, 4-dichlorophenyl)-N,N-dimethylureal, PRE metolachlor followed by POST diuron, and PRE pendimethalin -ethylpropy l)-3,4-dimethyl-2,6-dinitrobenzenamine] followed by POST oxyfluorfen p lus metribuzin hylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one]. PRE pendimethalin followed by POST oxyfluorfen plus diuron provided adequa te weed control in most residue removal systems, but was marginal in t he least thorough residue removal system. With properly chosen herbici de treatments, seed certification standards for perennial ryegrass can be met without field burning.