Managing water for weed control in rice.
Deep water flooding (up to 8 inches) provided considerable control of weeds in rice in large scale water management studies in Sutter Country, California. Under deep water flooding, Echinochloa crus-galli, E. oryzoides and Cyperus difformis were strongly suppressed, while Ammannia spp. were slightly or moderately affected and Heteranthera limosa and Scirpus mucronatus were little if at all affected. Molinate (as Ordram 10G) at 5 lb/acre gave adequate control of grasses under all water treatments except shallow flood (2 inches) and late drain regimes. The activity of bentazone (as Basagran) at 1 lb/acre + oil, applied for control of broadleaved species and sedges, was also affected in some instances by water treatment, though it gave excellent control of S. mucronatus and Ammannia spp. irrespective of water regime. The long-grain rice cv. L-202 was sensitive to changes is sowing rate and water depth, while the other cv. tested (S-201, M-201, M-202, M-401 and A-301) were generally less responsive.