Crop-weed competition in direct seeded low land and upland bunded rice.
Echinochloa crus-galli and E. colonum were the predominant grass weeds in lowland and upland bunded rice, resp. These weeds competed with rice at all stages. Among sedges, Cyperus difformis was the major weed and its competition was severe in early stages under lowland conditons. C. iria was the most predominant weed both under lowland and upland bunded rice, while Ammannia baccifera and Marsilea quadrifoliata were present only under lowland conditions. During the monsoon and summer seasons, an unchecked weed growth in lowland rice caused 53% reduction in paddy yield, while under upland bunded rice the yield reduction was about 91%. For higher yield in lowland rice, the crop should be kept free from weeds during the first 50 days in the monsoon season and 30 days in the summer season. In upland bunded rice, a weed-free condition of 60 days in the monsoon and 70 days in the summer season was essential.