Yellow nutsedge (Cyperus esculentus) is one of the most troublesome perennial weeds infesting cotton in the irrigated West. Purple nutsedge (Cyperus rotundus) is a lesser problem. Infestations have intensified within the past 10 to 15 years, in part due to the effective control of annual weeds and other perennials such as johnsongrass. Cultivation equipment has contributed to spreading infestation within and between fields. Nutsedge can be an early-season pest emerging with the cotton. If nutsedge is left to compete with the crop during the first few weeks of crop establishment, yield losses can be severe. Control of nutsedge has been difficult and somewhat unsuccessful. Preplant incorporated dinitroaniline herbicides do not provide control. Alachlor has given effective control, but cotton tolerance is questionable. Shallow cultivation with knives previous to planting will dislodge early emerging nutsedge and reduce its competitiveness. Close cultivation and/or hand weeding plus postemergence applications of methanearsonate herbicides (DSMA and MSMA) have provided control during the early stages of crop development. The competitiveness of later emerging nutsedge is severely reduced due to cotton shading.