Resumen
- Continuous irrigated rice cropping in LAC has resulted in chronical and difficult to control weed problems, such as red rice (Oryza sativa L.) and Echinochloa spp. Red rice alones is responsible for 20% production losses in the region (De Souza, 1989). Farmers rely heavily on herbicides for weed control, spending annually 218 million US dollars. Often, farms lack adequate soil levelling and water control to suppress weed growth with a permanent flood, thus weeds can emerge in successive flushes throughout the growing season prompting for repeated herbicide applications. Seventy percent of the land under irrigated rice is leased (L. R: Sanint, 1996, pers. Comm.), and for these farmers the burden of weed control costs is particularly heavy. With two or more rice crops a year, herbicides are repeatedly used on the same fields, and the repeated use of propanil to control E. colona, has resulted in the spread of propanil resistant biotypes of this weed (Fischer et al., 1993). Resistance of E. colona biotypes to other rice herbicides has also been reported (Caseley et al., 1995).