The herbicide S-ethyl hexahydro-1H-azepine-1-carbothioate [molinate] at 0, 3, and 6 lb/A was applied to drill-seeded rice [Oryza sativa L.] into the irrigation water at 8, 13, and 20 days after rice and weed emergence; the plots remained flooded for 2, 7, or 12 days. Three lb/A applied when weeds had 1 to 6 leaves and rice had 2 to 8 leaves controlled barnyardgrass [Echinochloa crusgalli (L.) Beauv.] and broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash] and did not injure rice when the water remained for 7 or 12 days. Weed control and yield of rice were reduced when the irrigation water was held for only 2 days. When the weeds were tillering, molinate controlled barnyardgrass better than it controlled broadleaf signalgrass. Molinate at 0, 3, and 6 lb/A was applied to drill-seeded rice into the irrigation water 1 week after rice and weed emergence; 7 days later the water was either left on the plots or was drained for 5, 10, 20, or 29 days. Three lb/A usually prevented reinfestations of barnyardgrass when plots were drained for 5, 10, or 20 days. Barnyardgrass reinfested rice drained for 29 days and reduced yields.