Evaluation of herbicides efficacy and selectivity for weed management in transplanted rice and the response of succeeding cowpea to herbicide residues

AbstractA field experiment was undertaken in India’s eastern sub-Himalayan plain during the Kharif seasons of 2021 and 2022 to evaluate various weed management options in transplanted rice and examine herbicides residual effects on succeeding cowpea crop. Among the treatments evaluated, early post-emergence application (EPoE) of bispyribac-sodium 35 g/ha + pyrazosulfuron-ethyl 26.25 g/ha with a silicon-based non-ionic surfactant at 5 ml/l, recorded significantly higher reduction of weed density (83.3%), weed biomass (83.0%) with higher weed control efficiency (WCE) (85.3%) at 60 days after application (DAA). Bispyribac-sodium 35 g/ha + pyrazosulfuron-ethyl 26.25 g/ha EPoE recorded higher benefit:cost ratio of 2.11 and outperformed manual weeding twice in terms of rice grain yield, straw yield, and net returns. Pyrazosulfuron- ethyl 15 g/ha EPoE was effective against broad-leaved weeds, while bispyribac-sodium 25 g/ha EPoE performance was better against grasses and sedges (WCE of 65-66%). The emergence, plant stand, growth, or yield of subsequently grown cowpea was unaffected by residues of herbicides sprayed in transplanted rice proving that all herbicide treatments tested were safe to crops in rice-cowpea cropping system.