Abstract

A field experiment was carried out at the Agricultural Experimental Farm of Calcutta University, Baruipur, South 24 Parganas situated in the lower Gangetic Delta region of West Bengal during spring season of 2016 and 2017 to find out the efficacy of sequential application of herbicides on weed growth and yield of greengram Wilczek. The experimental site was silty clay loam in texture, medium in organic carbon (0.66%), available N (174.3 kg/ha), available phosphorus (29.5 kg/ha) and available potassium (257.2 kg/ha) with PH 7.1. There were altogether 8 treatments of pre-emergence and post-emergence herbicides namely butachlor 1.5 kg /ha, pretilachlor 1kg /ha and pendimethalin 1kg /ha as a pre-emergence application, butacholor 1kg /ha followed by imazethapyr 0.1kg /ha, pretilachlor 0.75kg /ha fb imazethapyr 0.1kg /ha, pendimethalin 0.75kg /ha fb imazethapyr 0.1kg /ha, weed free check, and unweeded control. The experiment was conducted in randomized block design with three replications. The pre-emergence herbicides were applied one day after sowing of the crop and post-emergence herbicide was applied twenty days after sowing of the crop. The cultivar used for the experiment was “SML-668”. The crop was sown on 29th March and 15th March and harvested on1st June, and 20th May, in 2016 and 2017 respectively. Broad leaved weed Melochia corchorifolia was most pre-dominant during both the year of experimentations. As regards the relative density on per cent basis, there were 95% broad leaf, 4% grasses and only 1% sedges. Each and every herbicide formulation was found effective in arresting weed growth and proved to be superior in enhancing the yield of greengram over unweeded control. Among the three pre-emergence herbicides, pendimethalin was found to be best. Sequential application of herbicides i.e. pre-emergence fb post-emergence application is better than only single pre-emergence application of herbicides with regards to weed control efficiency and weed index. Weed free check treatment recorded highest production of greengram seed. But in economic point of view, all the three tested pre-emergence herbicides fb post-emergence application of herbicide imazeythapyr 0.1 kg /ha recorded higher benefit cost of ratio and were found quite superior to weed free check treatment. Pendimethalin 0.75kg/ha as a pre-emergence application fb post-emergence application of imazethapyr 0.1 kg /ha was recorded highest benefit and cost ratio. All the tested herbicides were found to be safe to the greengram crop with respected to phytotoxicity observed visually during spring season of 2016 and 2017.