Weed Management on Direct Seeded Rice.

Weeds are often the most serious problem in dry direct seeded rice (DDSR), causing reductions in yield and profitability. The effects of 10 weed management practices were evaluated to identify the most effective and economical methods of managing weeds in DDSR during the rainy season of 2010 at Chitwan, Nepal. Forty-seven weed species belonging to 13 families were observed in the experimental plots. Total weed infestations (uncontrolled) reduced grain yield up to 71%. Postemergence application of bispyribac-sodium at 25 g ha^-1 recorded the lowest (P<0.05) yield loss (9 %), and a greater benefit-cost ratio (B:C ratio) (2.36). Pendimethalin as preemergence followed by bispyribac-sodium gave the season-long weed control as compared to 2,4-D and bispyribac alone. Weed control efficiency ranged from 95.0% to 98.5% among the weed control methods. All the weed control treatments were equally effective in realizing higher grain yields on par with the weed-free plots (5.93 Mg ha^-1). The exceptions were brown-manuring with Sesbania aculeate L. (4.39 Mg ha^-1, P<0.05) where sesbania killed at 25 DAS, and oxadiargyl at 112 g ha^-1 (4.69 Mg ha^-1) applied at 10 DAS. These showed lower grain yield (P<0.05) and B:C ratio (P<0.05) than other weed control practices. An integrated application of pendimethalin with bispyribac-sodium was effective in controlling weeds in producing greater yield, while a single application of bispyribac-sodium at 25 g ha^-1 applied at 22 DAS found economically superior to all other weed management treatments.