A preliminary study on the time of application of imazethapyr and its ready mix combination with pendimethalin and imazamox against weeds in blackgram

The bio-efficiency of imazethapyr and its ready mix combination products with pendimethalin and imazamox against weeds, their effect on growth, yield and phytotoxic effects on black gram and residual effect on succeeding mustard crop were studied during 2013-14. Significantly lower weed count and dry weight was recorded with application of imazethapyr + pendimethalin (pre-mix) at 800 g/ha, pendimethalin at 1000 g/ha and imazethapyr + pendimethalin (pre-mix) at 900 g/ha. Imazethapyr + pendimethalin (pre-mix) 1000 g/ha and 800 g/ha, pendemethlin 1000 g/ha and imazethapyr 50 and 70 g/ha (pre emergence) behaving statistically similar with pendimethalin 1000 g/ha (pre emergence) and hand weeding at 20 and 40 days after sowing resulted in significantly higher seed yield of black gram. Seed yield of blackgram was negatively associated with total weed count and weed dry weight (P≤0.01). With every one weed increase per square meter, the blackgram seed yield was expected to reduce by 16.8 kg/ha. Net returns, B:C and net returns over weedy check were highest under imazethapyr + pendimethalin 900 g/ha. The economic threshold levels i.e. No m-2 and g m-2 with the weed management practices studied varied between 1.7 – 18.0 m-2 and 1.0-10.0 g m-2. Imezethapyr + pendimethalin 1000 g/ha and imazethapyr + imazamox 50 g/ha had lowest weed persistence index (WPI). Imazethapyr + pendimethalin 900 g/ha resulted in highest crop resistance index. Weed management index (WMI), Agronomic management index (AMI), and Integrated weed management index (IWMI) were highest following imazethapyr 40 g/ha. Overall impact index (Ii) was highest under imazethapyr 50 g/ha followed by imazethapyr + pendimethalin 900 g/ha, imazethapyr + pendimethalin 1000 g/ha and pendimethalin 1000 g/ha. Weed index (WI) indicated 70.8% loss in yield of blackgram. The residual effects of herbicide treatments on succeeding mustard crop were not observed.