Abstract

                                Field experiments were conducted during kharif 2011 and rabi 2011 -12 at Rice Research Station, Moncompu, Kerala to study the efficacy of herbicides for weed control in direct seeded rice. The experiments were conducted in RBD with seven treatments comprising of two early post emergence herbicides, two post emergence herbicides, weed free situation, hand weeding twice at 20 and 40 DAS and unweeded check in plots of 25 m2 .The major weeds found in the experimental field were; Echinochloa stagnina (Retz.) P. Beauv., Echinochloa glabrescens Munro ex Hook. f., Fimbristylis miliacea (L.)Vahl, Cyperus difformis L., Cyperus iria L., Schenoplectus pungens (Vahl) Palla, Monochoria vaginalis (Burm. f.) C. Presl ex kunth, Ludwigia perennis L. and Sphenoclea zeylanica Gaertner. Results of the study indicated that predominance of weed flora depended on the season. Grassy weeds predominated during kharif season and sedges predominated during rabi season. All the weed control treatments significantly reduced the density and dry weight of weeds which resulted in significantly higher growth and yield of rice over unweeded control. Results also indicated that early post emergence herbicides like pyrazosulfuron ethyl 10% WP and bensulfuron methyl + pretilachlor (6.6 GR) were found effective in controlling sedges and broad leaved weeds, while the post emergence herbicides, bispyribac sodium was found effective against grassy weeds and broad leaved weeds and penoxsulam was found effective against grassy weeds and sedges. During both seasons weed free situation recorded the highest grain yield. Among the herbicide treatments, post emergence application of bispyribac sodium 10% SC @ 30 g ai/ha and penoxsulam24 SC @ 25 g ai/ha and early post emergence application of pyrazosulfuron ethyl 10 % WP @ 20 g ai/ha recorded higher yield which was on par with each other with better weed control efficiency and low weed index.

Key words : Direct seeded rice, weed density, weed dry matter, weed control efficiency, weed index