Effect of Pre and Post Emergence Herbicides on Growth and Yield of Bt Cotton under Varied Agro Meteorological Environments

Successful weed control is essential for economic cultivation of cotton. The greatest competition of weeds usually occurs early in the growing season. Cultural methods adopted by farmers are time consuming and expensive. Also herbicide applied at the time of sowing will not give season long control of weeds. Pre-emergence applications has the initial advantage of cotton over the weeds. Once this achieved, then post-emergence directed applications can be utilized to extend the weed control throughout the cropping season. Hence that, objective to evaluate pre and post emergence herbicides in varied environment condition resultant of time of sowing in cotton. Pendimethalin is dinitroanaline family of herbicides was registered for cotton in 1975 [1]. Pendimethalin controls weed by inhibition of microtubule formation in cells. This causes disruption of cell division. As the microtubule spindle fibers that guide chromosomes are absent, the cell plate does not appear and cells do not divide. The microtubules are also responsible for microfibril orientation in the cell wall. In their absence, microfibrils become disoriented and cells expand to a rounded rather than elongated shape. It is a pre-emergent herbicide controlling a wide range of grass and small seeded broadleaf weeds [2]. Pyithiobac sodium is a broad spectrum systemic herbicide, which inhibits enzyme acetolacetate synthase, a key enzyme in biosynthesis of branched chain amino acids. It is reported to control troublesome broadleaf weeds when applied as post emergence herbicide at 2-3 leaf stage) without affecting the cotton [3]. Quizalofop ethyl is a selective systemic herbicide, applied at post emergence herbicide for the control of annual and perennial grass weeds. It is a biochemicaly Acetyl CoA carboxylase inhibitor; inhibition of fatty acid biosynthesis and mode of action systemic herbicide, absorbed from the leaf surface, with translocation throughout the plant, moving in both the xylem and phloem, and accumulating in the meristematic tissue.