A field experiment was conducted at Cotton Research Station, Srivilliputtur from October 2017 to February 2018 to optimize spacing and time and dose of defoliant application to suit high-density planting system in cottonunder irrigated conditions. The experiment was conducted in a split-plot design with three replications. The treatments consisted of three levels of plant spacings (100 x 10 cm, 60 x 15 cm and 75 x 30 cm) in main plot and four treatments with time and doses of defoliant application of Dropp Ultra (Tembotrione 34.4 % SL) at 200 ml/ha at 120 DAS, 200 ml/ha at 130 DAS, 2000 ppm (500 ml/ha) at 120 DAS and 2000 ppm (500 ml/ha) at 130 DAS were accommodated in subplot. The results revealed that though the normal spacing of 75 x 30 cm produced higher number of sympodial branches and bolls per plant, it was comparable with that of HDPS with 100 x 10 cm spacing. Among the three spacings, 100 x 10 cm with a plant population of 1,00,000 plants/ha (HDPS) registered the highest seed cotton yield of 2063 kg/ha which was comparable with closer spacing of 60 x 15 cm with 1,11,111 plants/ha (1947 kg/ha) and significantly superior than the existing recommended spacing of 75 x 30 cm with 44,444 plants/ha (1779 kg/ha). Higher gross income, net income and higher benefit-cost ratio were also recorded with HDPS followed by 60 x 15 cm. Dropp ultra application at the rate of 200 ml/ha on 130 DAS was found to be effective for higher seed cotton yield and economic benefits.
Key words : Cotton, spacing, defoliant, seed cotton yield, economics.