Vol. 5 No. 2
Effect of herbicides on weed-crop association in wheat.
Abstract: Terai region has the characteristic of high rainfall and high humidity triggering aggressive growth of weeds, which in turn, become one of the major constraints in crop production during rabi season. The major weed flora observed in experiment were Polygonum orientale, P. pensylvanicum, P. persicaria, Stellaria media, S. aquatica, Oldenlandia diffusa, Hydrocotyl ranunculoides, Physalis minima, Eclipta alba, Cynodon dactylon, Setaria glauca and Digitaria sanguinalis. Three years study in wheat indicated that continuous application of 2,4-D, pendimethalin and metribuzin triggered shifting of weed flora. Continuous use of 2,4-D triggered emergence of Physalis minima in the place of several species of Polygonum, a common weed flora in wheat and that Physalis minima was not controlled even at higher dose of 2,4-D (0.8 kg ha-1). Physalis minima was also not controlled with the use of metsulfuron methyl at its higher dose (16 g ha-1). Similarly in sole pendimethalin treated plot, shifting was observed in favour of Hydrocotyl ranunculoides and Eclipta alba and that led to significant yield reduction in third year of experimentation. Application of metribuzin led to the emergence of Solanum nigrum which was completely absent in all other herbicide treated plots including weedy control treatment. Emergence of grasses was also observed in metribuzin treated plots of wheat. In integrated weed management practices, pendimethalin 0.5 kg ha-1 + hand hoeing at 35 days after sowing recorded higher weed control efficiency (81-86%) and yield (43.90q ha-1) which was comparable to complete weed free situation (44.50 q ha-1) and farmer’s practices (44.31 q ha-1) with highest net return (Rs. 38733/-) and benefit cost ratio (1.93)..
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