Plots in dense quackgrass (Agropyron repens) sods were treated with 5-bromo-3-isopropyl-6-methyl uracil (isocil) or 5-bromo-3-sec-butyl-6-methyl uracil (bromacil) at rates of 0.5 to 4.0 lb/A in the fall or in the early spring and then planted to corn. Quackgrass was virtually eliminated by all rates but 0.5 lb/A. Corn was severely injured on plots treated at 2 lb/A but made fair growth at rates of 1.0 lb/A or less. The year following corn, soil residues of isocil were more toxic to oats than those of bromacil. Carbohydrate analyses of rhizomes from treated plots indicated that depletion of carbohydrate reserves contributed to the elimination of the quackgrass.