Weeds in direct seeded ricefields of Thanjavur District, Tamil Nadu.
Weeds of direct-(dry) sown rice were surveyed 60 d after sowing in 3 cropping seasons: kuruvai (June-July to Sep.-Oct.) and thaladi (Sep.-Oct. to Feb.-Mar.) in double crop wetlands and samba (Aug-Sep. to Jan-Feb.) in single crop wetlands. The major graminaceous weeds were Echinochloa colona [E. colonum], E. crus-galli and Chloris barbata. The most common Cyperaceae were Cyperus rotundus, C. iria, and Fimbristylis miliacea. Of 9 families of dicots present, Onagraceae, Marsileaceae, and Compositae were the most important. Weed density was highest during the samba season due to the favourable moisture and climatic conditions. Weed flora during kuruvai consisted of nearly equal densities of monocots and dicots. During thaladi and samba, monocots were dominant. Irrespective of season, E. colonum was the major grass weed (50-81%), C. rotundus (50-65%) dominated the sedges and Ludwigia adscendens and Marsilea quadrifolia (30-50%) dominated the broadleaved weeds.