Abstract

Field experiment was conducted during rabi seasons of 2012–13 and 2013–14 at Agricultural Research Institute, Patna to find out the bio-efficacy of herbicides for controlling weeds in linseed in comparison to hand weeding twice at 20 and 40 days after sowing. The most predominant weed flora observed in the experimental plots were broad leaf weeds like Rumex dentatus, Chenopodium album, Polygonum plebejium, Alternenthera sesilis, Physalis minima, Medicago polymorpha and Solanum xanthocarpum, grasses like Cynodon dactylon, Digitaria sanguinalis and sedges like Cyperus rotundus. The herbicide treatments include pre-emergence application of pendimethalin @ 1000 g a. i./ha, pendimethalin 30 EC + imazethapyr 2 EC @ 750 and 1000 g a. i./ha and post-emergence application of isoproturon 75 WP @ 1000 g a. i./ha, clodinafop 15 WP @ 60 g a. i./ha and imazethapyr 10 SL @ 40, 60, 75 and 100 g a. i./ha. The results showed that application of pendimethalin 30 EC + imazethapyr 2 EC @ 750 and 1000 g a. i./ha as pre-emergence showed inhibitory effect on the linseed seedlings. Safe herbicide pendimethalin 30 EC @ 1000 g a. i./harecorded lowest weed biomass with highest weed control efficacy (91.5%) which was at par with isoproturon 75 WP @ 1000 g a. i./haas post-emergence with weed control efficacy of 89.9%. The manually weeded plot recorded the highest seed yield of 1337 kg/haamong all the treatments, whereas maximum seed yield among the herbicide treatments was obtained with post-emergence application of isoproturon 75 WP @ 1000 g a. i./ha (1195 kg/ha), which was found statistically at par with pre-emergence application of pendimethalin 30 EC @ 1000 g a. i./ha (1177 kg/ha), post-emergence application of imazethapyr 10 SL @ 60 g a. i./ha (1110 kg/ha) and with manually hand weeding twice. In terms of profitability, post-emergence application of isoproturon 75 WP @ 1000 g a. i./hagave the highest net returns, B: C ratio and incremental B: C ratio than all other weed control treatments.