Bispyribac-sodium, Impact assessment, Transplanted rice, Weeds

Different doses of bispyribac-sodium 20, 25 and 30 g/ha were evaluated against mixed weed flora in transplanted rice under mid-hill conditions of Himachal Pradesh during 2010 and 2011. Major associated weeds were Echinochloa colona (31.1%) and Commelina benghalensis (7.3%) among grasses, Cyperus iria (26.9%) and Scripus (9.3%) among sedges and Ammania baccifera (8.8%) among broad-leaved weeds. Bispyribac-sodium 20-30 g/ha effectively controlled E. colona. Cyhalofop-butyl/butachlor fb metsulfuron-methyl was comparable to bispyribac-sodium in controlling C. benghalensis. Bispyribac-sodium brought about significant reduction in the count of Cyperus sp. up to 60 days after transplanting (DAT). Bispyribac-sodium 30 g/ha behaving statistically similar with bispyribac-sodium 20 and 25 g/ha resulted in significantly lower total weed count and total weed dry weight. There was no phytotoxicity of bispyribac-sodium on rice and no residual toxicity on succeeding crop of wheat. Bispyribac-sodium, farmer’s practice, cyhalofop-butyl fb metsulfuron-methyl and cyhalofop-butyl fb 2,4-D were comparable in influencing rice grain yield. Rice grain yield was positively associated with plant height, panicle length, effective tillers and spikelets/panicle and was negatively associated with weed count and weed biomass. With one weed per m2 increase up to harvest, grain yield of rice was expected to decrease by 15.3 kg/ha. Bispyribac-sodium at 30 kg/ha was the best in terms of net returns due to weed management. Cyhalofop-butyl fb metsulfuron-methyl gave the highest net profit/rupee invested. Herbicide efficiency index (HEI) was highest and weed index was lowest under bispyribac-sodium 30 g/ha. Weed management index (WMI) and agronomic management index (AMI) were highest under cyhalofop-butyl fb metsulfuron-methyl.