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A field experiment was conducted at Punjab Agricultural University, Ludhiana to study the efficacy of post-emergence herbicides for weed control in soybean. The herbicides (pendimethalin, imazethapyr, imazethapyr + imazamox and quizalofop-p-ethyl) did not show any significant adverse effects on the number, dry weight and leghaemoglobin content of nodules. Application of pendimethalin 0.45 kg/ha as pre-emergence (PE) + hand weeding (HW) at 40 days after sowing (DAS) recorded significantly higher seed yield than other treatments, however, it was at par with two hand weeding. Among the herbicides, imazethapyr at 75 g/ha applied at 3 weeks after sowing (WAS) recorded significantly higher seed yield than pendimethalin 0.45 kg/ha (PE) and weedy check and was at par with imazethapyr + imazamox 70 g/ha and quizalofop-p-ethyl 50 g/ha applied at 3 WAS. Application of pendimethalin 0.45 kg/ha (PE) + HW at 40 DAS provided the highest net returns (‘ 49496/ha) followed by two hand weedings. However, application of post-emergence herbicides imazethapyr at 75 g/ha and imazethapyr + imazamox 70 g/ha at 3 WAS were found promising in controlling weeds, providing optimum seed yield and higher B:C ratio. In case of scarcity of labour, post-emergence herbicides can play an important role in controlling weeds effectively.
Virk et al. (Mon,) studied this question.