Influence of Residue Removal Method and Herbicides on Perennial Ryegrass Seed Production: II. Crop Tolerance

Inherent in the ongoing transition from open-field burning to nonburn systems for grass seed production in the Pacific Northwest is an increased reliance on herbicides for weed control. However, herbicide treatments able to control volunteer crop seedlings, the most abundant weed in certified grass seed fields, may pose severe hazards to the established crop itself. Fourteen herbicide treatment sequences plus an untreated check were examined in five residue removal systems at two sites during two consecutive growing seasons to determine their impact on perennial ryegrass (Lolium perenne L.) seed yield. Seed yield was reduced by weed competition in nonburned, untreated checks, and by herbicide injury in some of the 14 herbicide treatment sequences. When compared across 13 promising herbicide treatments, seed yield did not differ between burned and nonburned plots in the first year, although burning was slightly superior in the second. However, the cumulative yield advantage to burning was only 84 kg ha−1 , or 2.6%, over the 2-yr period. Although differences in yield among four herbicides applied preemergence (PRE) to seedling grasses in mid-October were relatively small, pendimethalin [N-(l-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] and oxyfluorfen [2-chloro-l-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] were superior to either metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl)acetamide] or trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] in specific instances. When applied following PRE herbicides, early December postemergence (POST) applications of 1.8 kg ha −1 diuron [N'-(3,4-dichlorophenyl)-N,N-dimethylurea] or 0.14 kg ha−1 oxyfluorfen plus 1.3 kg ha −1 diuron generally did not differ in yield. While there was usually little net effect on seed yield of applying POST herbicides following pendimethalin, they did depress yield 129 kg ha−1 the first year in burned plots, while increasing it an average of 79 kg ha~* the second year in all plots. With properly chosen herbicide treatments, the impact on perennial ryegrass seed yield of changing to nonburned methods of residue removal should be minimal. If such herbicide treatments are not available, however, the elimination of field burning may seriously disrupt perennial ryegrass seed production. Contribution of the USDA-ARS in cooperation with the Oregon State Univ. Agric. Exp. Stn. Oregon State Univ. Tech. paper no. 10,214.