Influence of Residue Removal Method and Herbicides on Perennial Ryegrass Seed Production: I. Weed Control

Grass seed production in the Pacific Northwest is in transition from reliance on open-field burning to systems integrating mechanical removal of postharvest crop residues with chemical weed control. Field tests of the ability of these systems to meet current seed certification standards wash while maintaining normal seed yields were initiated in 1989. Fourteen herbicite treatment sequence plus an untreated check were evaluated under five residue removal systems at two sites during two consecutive growing seasons. Residue removal method were three nonburn systems varying in thoroughness of residue removal and two methods of burning. Among the nonburn systems, adequate control of volunteer perennial rye grass (Lolium perenne L.), the most abundant weed in all tests, was most readily achieved in plots where residue was most thorougly removed. Herbicide treatments providing the best weed control in both years at both sites included preemergence(PRE) metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide] followed by postemergen(POST) oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethlyl)benzene)] plus Diuron [N−3, dichlorophenyl)-N,N-dimethylurea],PRE metalochlor followed by POST diuron, and PRE pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] followed by POST oxyfluorfen plus metribuzin] [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-124 triacin-5(4H)-one]. PRE pendimethalin followed by POST oxyfluorfen plus diuron provided adequate weed control in most residue removal systems, but was marginal in the least thorough residue removal system. With properly chosen herbicide treatments, seed certification standards for perennial ryegrass can be met without field burning. Contribution of the USDA-ARS in cooperation with the Oregon State Univ. Agric. Exp. Stn. Oregon State Univ. Tech. paper no. 10,213.