Research on weed management in furrow-irrigated rice is needed as water availability becomes more limited in rice production regions of Arkansas. Research was conducted at Keiser and Pine Tree, AR, with the objectives being to determine (1) whether the addition of clomazone to imazethapyr would improve PRE weed control in furrow-irrigated, imidazolinone-tolerant rice, and (2) whether increasing the imazethapyr rates would improve weed control without injuring rice. Imazethapyr was applied at 70, 87.5, and 105 g ai/ha PRE with and without clomazone followed by imazethapyr POST at the same rate as used PRE. No rice injury was observed during the growing season at either site. Clomazone plus imazethapyr applied PRE did not improve early season control of Palmer amaranth, pitted morningglory, prickly sida, barnyardgrass, or broadleaf signalgrass over imazethapyr alone. Increasing the PRE imazethapyr rate to 105 g/ha did not improve Palmer amaranth or pitted morningglory control. Imazethapyr applied PRE on a clay soil generally provided lower weed control than on the silt loam soil. Increasing the imazethapyr rate did not improve rice yields.

Nomenclature: Clomazone, imazethapyr, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, broadleaf signalgrass, Urochloa platyphylla (Nash) R.D. Webster BRAPP. Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, pitted morningglory, Ipomoea lacunosa L. IPOLA, prickly sida, Sida spinosa L. SIDSP, rice, Oryza sativa L. ‘CL 730’ ORYSA