Dose and time dependent efficacy alteration of different defoliants on seed cotton yield

Field experiments were conducted during 2012 and 2013 to determine the effect of select defoliants i.e dropp ultra and ethrel, their optimal dose and suitable time of application on earliness and seed cotton yield in 3 American cotton cultivars. MRC7361BGII (3055.2 kg ha(-1)) and MRC7017BGII (2913.0 kg ha(-1)) resulted in significantly improved seed cotton yield as compared to F1 861 (2346.0 kg ha(-1)). Dropp ultra? @ 200 ml ha(-1) revealed highest yield (3018.7 kg ha(-1)) followed by ethrel @ 2000 ppm (2820.1 kg ha(-1)) and control (2730.0 kg ha(-1)) , while statistically least yield (2516.9 kg ha(-1)) was observed with higher dose of dropp ultra @ 225 ml ha(-1). Defoliants applied 150 days after sowing (DAS) resulted in significantly better yield (2853.3 kg ha(-1)) as compared to the early application at 140 DAS (2689.5 kg ha(-1) owing to improvement in open bolls and boll weight. Pooled data indicated that dropp ultra @ 200 ml ha(-1) has potential to promote crop earliness, better boll opening and their retention by keeping vegetative and reproductive growth in harmony to enhance seed cotton yield.