Effect of post-emergence application of imazethapyr on symbiotic activities, growth and yield of blackgram (Vigna mungo) cultivars and its efficacy against weeds

A field experiment was conducted during the rainy (kharif) season of 2008 and 2009 at Ludhiana, Punjab to study tolerance of different blackgram [Vigna mungo (L.) Hepper] cultivars to post-emergence application of imazethapyr and its efficacy on weeds. The experiment was laid out with 8 weed-control treatments, viz. imazethapyr at 3 application rates (50, 75 and 100 g/ha) sprayed at 15 and 25 days after sowing (DAS), 2 hand-weedings (20 and 40 DAS) and unweeded control and 2 blackgram cultivars (‘Mash 114’ and ‘Mash 338’). Both the cultivars showed good degree of tolerance to imazethapyr sprayed at different doses and at different times. Post-emergence application of imazethapyr had no adverse effect on shoot dry weight as well as root dry weight of blackgram cultivars. Number of nodules, dry weight of nodules and leghaemoglobin content were the highest in imazethapyr 100 g/ha sprayed at 15 DAS, being statistically at par with 2 hand-weedings (20 and 40 DAS). imazethapyr application at 75 and 100 g/ha at 15 DAS resulted in effective control of weeds which was comparable to that of 2 hand-weedings. Application of imazethapyr at 100 g/ha at 15 DAS resulted in 62.0% higher grain yield over the unweeded control. Imazethapyr at 100 g/ha at 15 DAS also recorded the highest gross and net returns of 41,400 and 29,800 respectively, which was closely followed by imazethapyr at 100 g/ha sprayed at 25 DAS and 2 hand-weedings.