Ethofumesate (2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate) applied preemergence or early postemergence at 0.8 to 4.5 kg/ha eliminated annual bluegrass (Poa annua L.) in Italian ryegrass (Lolium multiflorum Lam.) seed fields. Rattail fescue (Festuca myuros L.) was more difficult to control. The 0.8 kg/ha rate controlled only 55% of the rattail fescue. Rates of 1.1 to 1.7 kg/ha controlled 72 to 95% and rates of 2.2 to 4.5 kg/ha eliminated rattail fescue. All ethofumesate treatments except one, 2.2 kg/ha applied postemergence in Experiment 7, reduced weed competition enough so that ryegrass seed yields were increased. At 4.5 kg/ha, a rate double that required to eliminate rattail fescue, seed yields were as high or higher than at 2.2 kg/ha rate, indicating that ethofumesate has at least a twofold safety margin on Italian ryegrass. The germination of ryegrass seed harvested from plots treated with ethofumesate at 0, 2.2, and 4.5 kg/ha was not affected by the treatments.