Weed control by pyrazosulfuron-ethyl and its influence on yield and economics of transplanted rice

A field experiment was conducted on a silty clay loam soil at Palampur, Himachal Pradesh during Kharif 2016 and 2017 to assess pyrazosulfuron-ethyl as an alternative herbicide to manage weeds in transplanted rice. Ten treatments comprised of company released sample of pyrazosulfuron-ethyl at 10, 15, 20 and 30 g/ha was compared to its market sample at 10 and 15 g/ha, bispyribac-sodium at 20 and 40 g/ha, hand weeding twice and weedy check. Pyrazosulfuron-ethyl and bispyribac-sodium effectively reduced the biomass of Echinochloa colona, Echinochloa crusgalli and Cyperus difformis. These herbicides also suppressed the growth of Ammannia baccifera, but not to the extent as hand weeding twice. Pyrazosulfuron-ethyl curtailed Eclipta alba, but lower dose of bispyribac-sodium was not effective against it. In 2016, pyrazsulfuron-ethyl 20 g/ha gave significantly higher yield while in 2017, pyrazsulfuron-ethyl 30 g/ha gave significantly higher yield of rice over other weed control treatments. Every gram weed biomass increase per square metre caused 5.6 kg/ha yield reduction of transplanted rice. Samples of pyrazosulfuron-ethyl obtained directly from the industry had an edge over the market samples. Weed persistence index was found to be decreased and crop resistance index increased corresponding to increase of dose of pyrazosulfuron-ethyl and bispyribac-sodium. The minimum weed index was under company's pyrazosulfuron-ethyl at 20 g/ha followed by 15 g/ha, 30 g/ha and market's sample at 15 g/ha. Cost of weed control was 3.0 to 4.7% of the total cost with pyrazosulfuron-ethyl and 6.1 to 9.8% with bispyribac-sodium. Company procured pyrazosulfuron-ethyl at 15 and 20 g during 2016 and at 20 and 30 g/ha during 2017 had higher net returns and marginal benefit cost ratio (MBCR). Eighty per cent of applied pyrazosulfuron-ethyl got degraded within 5 days of its application. Residues of pyrazosulfuron-ethyl in grain and straw at the time of harvest were below detectable level (BDL) irrespective of treatments.