The field experiment was carried out at Bihar Agricultural University, Sabour, Bhagalpur, Bihar, India, during the Kharif season of 2018 to study the efficacy of pre- and post-emergence herbicides on suppressing weed flora and nutrients uptake by weed and blackgram (Phaseolus mungo) crop. The experiment was laid out with eleven treatments in a randomised complete block design with three replications. Nine weed species (one sedges, two grassy and six broad-leaved) belonging to eight families were found dominant in blackgram. Among the major sedges observed in the experimental plot, Cyperus rotundus (Cyperaceae) was the most dominant and aggressive weed. Some grass weeds were Echinochola colona (Poaceae) and Cynodon dactylon (Cyperaceae) whereas broad-leaved included Phyllanthus niruri ((Phyllanthaceae), Solanum nigrum ((Solanaceae), Trianthema portulacastrum (Aizoaceae), Cucumis melo (Cucurbitaceae), Cleome gynandra (Capparaceae) and Mimosa pudica (Fabaceae). A significant reduction in weed flora was observed in weed free plot, further among the herbicidal treatments’ pre-emergence application of pendimethalin 30 EC 75 kg/ha followed by imazethapyr 0.060 kg/ha as post-emergence reduced the weed flora at 15, 30, 45 and 60 Days after sowing respectively. The lowest nutrient depletion by weed, highest seed yield (925 kg/ha), net return ( 48549/ha), B: C ratio (2.65) and nutrient uptake by blackgram were recorded with pre-emergence pendimethalin 30 EC 0.75 kg/ha followed by imazethapyr 0.060 kg/ha as post-emergence.