Purple nutsedge (Cyperus rotundus) is a troublesome weed that outcompetes crops and contributes to poor yields. In the past, agriculturalists controlled purple nutsedge by fumigating soil with methyl bromide but the fumigant has since been classified as a controlled substance under the Montreal Protocol. This study evaluated the effectiveness of several alternative purple nutsedge control techniques and compared them with results obtained from the application of Roundup. Concentration treatment effects for the allelopathic seed powders of watercress and turnip were tested in a field trial while seed powders of yellow mustard and sunflower were tested in a potted trial. The allelopathic amendments significantly delayed weed emergence but several factors interfered with long-term effectiveness. Roundup was determined to be the most effective season-long weed control among the treatments consistently leaving the least amount of surviving weeds and underground organs.