Effect of chemical defoliation on boll opening percentage, yield and quality parameters of Bt Cotton (Gossypium hirsutum)

Abstract

A field experiment was conducted during kharif of 2008 and 2009 to study the effect of chemical defoliation on boll opening percentage (BOP), yield and quality parameters of Bt Cotton ( Gossypium hirsutum L.). The experi- ment was laid out in a randomized complete block design with four replications comprising twelve treatments, viz. control, thidiazuron 100, 150 and 200 g/ha, ethrel 1.0 and 1.5 l/ha applied at 40 or 60 BOP and gramoxone (paraquat) 1.0 l/ha applied after first picking. Defoliation with ethrel 1.5 l/ha at 60 BOP resulted in higher number of picked bolls/plant and BOP when compared with control. However, maximum seed cotton yield was obtained with ethrel at 1.0 l/ha (2.27 and 1.96 t/ha) and it was followed by thidiazuron 100 g/ha (2.21 and 1.92 t/ha) applied at 60 BOP. Gramoxone (paraquat) application at 1.0 l/ha after first picking failed to exert any significant influence on seed cotton yield and yield contributing characters. The B:C ratio of thidiazuron 100 g/ha at 60 BOP was compara- tively higher when compared with rest of the defoliation treatments. Seed index, lint index, ginning-outturn, oil content (%) in seeds and fibre quality parameters, viz. 2.5 % span length, fibre bundle strength and fibre fineness were not significantly influenced by any of the defoliation treatment.