Prevent new weeds with a preemergence herbicide with oxalis on the label. It spreads by seeds and aggressive underground stems, called rhizomes. Thoroughly dig out roots and pointed rhizomes - remaining pieces regenerate new plants. Spot-treat with a nonselective weed killer. Also called yellow nutgrass, it reproduces by seed and tubers that grow at the root tips.
Tubers often persist in the soil, making established plants difficult to control.
Mow high in early to midsummer and water infrequently though thoroughly. Spot-treat with postemergence herbicides labeled for nutsedge. As with most weeds, control is easiest when plants are small. Spotted spurge is a broadleaf annual that grows close to the ground in a fast-spreading mat. Its small leaves are green with a brown-red spot on top.