This experiment was conducted in a highly C. iria infested plot at "El Pelon" rice farm in Liberia, Costa Rica, to determine the control effectiveness of this weed by several hormonal and sulfonylurea herbicides and their selectivity to the rice crop, and to preliminarily estimate the negative effect of C. iria on the crop. The evaluated treatments included three new sulfonylureas, six herbicides recommended for cyperaceous and dicotyledonous control and an unweeded control. The herbicides were app!ied following each of the manufacturer's recommendations. The rice cultivar used was CR 1821 and the ground was kept saturated during the whole trial. The sulfonylurea herbicides, bensulfuron-ethyl and pyrazosulfuron-methyl, were the most effective in controlling C. iria, and they also were the highest yielding treatments. The herbicides commonly used for the cyperaceous control, showed intermediate control percentages of these weeds. When C. iria was not controlled, at approximately 30 days after planting, it completely covered the rice plants, completed its !ife cycle at 70 days and reduced the rice yield by 50%.