Technical Abstract: A field experiment was conducted in 2007 and repeated in 2008 in Pennsylvania to investigate weed control during switchgrass (Panicum virgatum L.) establishment. Quinclorac was applied postemergence at 0.28, 0.42, and 0.56 kg ai ha-1 with methylated seed oil and sulfosulfuron was applied at 0.039 and 0.069 kg ai ha-1 with nonionic surfactant. Herbicides were applied at four and six weeks after switchgrass planting. Sulfosulfuron caused 10 to 28% chlorosis and reduced switchgrass height up to 50% two weeks after application (WAA). In contrast, quinclorac injury ranged from 0 up to 47% chlorosis at the highest rate with height reductions from 0 to 27%. By 8 WAA, chlorosis was not apparent with either herbicide and evidence of stunting had mostly disappeared. Sulfosulfuron provided between 33 and 73% yellow foxtail [Setaria glauca (L.) Beauv.] control and greater than 82% yellow nutsedge (Cyperus esculentus L.) control. Smooth pigweed (Amaranthus hybridus L.) control ranged from 25 to 70%. Quinclorac provided 45 to 87% yellow foxtail control and had no activity on yellow nutsedge. Smooth pigweed control with quinclorac never exceeded 28%. Earlier applications were more effective on yellow foxtail for both herbicides, but quinclorac was the stronger summer annual grass herbicide. The primary benefit of sulfosulfuron in this experiment was control of yellow nutsedge and suppression of some broadleaf weeds. Total aboveground yield in the fall was highest and weed biomass was lowest in treatments that provided good weed control and that did not injure switchgrass. Future research should examine combinations of broadleaf and grass herbicides for broader spectrum control of weeds in switchgrass.