Impact of imazethapyr and its ready-mix combination with imazamox to control weeds in blackgram

The bio-efficiency of imazethapyr and its combination with imazamox or pendimethalin in comparison to hand weeding against weeds, their effect on growth, yield and phytotoxicity on black gram and residual effect on succeeding mustard crop were studied during 2014–15 and 2015–16. Hand weeding twice resulted in the highest overall weed control efficiency followed by pre-emergence application of imazethapyr + imazamox 80 g/ha, preemergence imazethapyr + imazamox 70 g/ha and pre-emergence imazethapyr + pendimethalin 1000 g/ha. Hand weeding twice and pre-emergence imazethapyr + pendimethalin 1000 g/ha were comparable to pre-emergence imazethapyr + imazamox 70 g/ha for seed yield. With every increase of one weed per square metre, the blackgram seed yield was reduced by 2.1 kg/ha. Similarly with every g/m2 increase in weed weight, the blackgram yield was subjected to fall by 5.1 kg/ha. The economic threshold levels i.e. No/m2 and g/m2 with the weed management practices studied varied between 8.3 - 42.0/m2 and 3.5–17.6 g/m2. Weed persistence index (WPI) was lowest and crop resistance index (CRI) was highest in the hand weeding twice treatment. Post-emergence application of imazethapyr 70 and 80 g/ha and imazethapyr + imazamox 70 and 80 g/ha caused mild toxicity during 2014 and had therefore lower crop resistance index. Efficiency index was the highest under hand weeding followed by preemergence application of imazethapyr + imazamox 80 g/ha, pre-emergence imazethapyr + pendimethalin 1000 g/ha and pre-emergence imazethapyr 80 g/ha. Weed index indicated 55.4% reduction in yield of blackgram due to weeds. Preemergence imazethapyr 80 g/ha, imazethapyr + imazamox 80 g/ha, imazethapyr 70 g/ha and imazethapyr + pendimethalin 1000 g/ha had higher overall impact index than hand weeding due to lower cost. Residual effect/phytotoxicity was not observed on succeeding crop of mustard during 2014 and 2015 as well.