Standardize the dose and timing of defoliant application to facilitate synchronized maturity for mechanical harvesting of rainfed cotton (Gossypium hirsutum)

A field experiment was conducted at Regional Research Station, Aruppukottai, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu during the winter (rabi) season of 2016 and 2017 at Aruppukotai, Tamil Nadu, to study the influence of defoliants on ‘SVPR 2’ (Gossypium hirsutum L.) rainfed cotton. The experiment was laid out in randomized block design with 3 replication. The treatments consisted of defoliants spraying at different concentrations and time of application, viz. ethrel @ 1,500 ppm at 135 days after sowing DAS (D₁), ethrel @ 2,000 ppm at 135 days after sowing (DAS) (D₂), ethrel @ 2,500 ppm at 135 DAS (D₃), ethrel @ 1,500 ppm at 150 DAS (D₄), ethrel @ 2,000 ppm at 150 DAS (d₅), ethrel @ 2,500 ppm at 150 DAS (D₆), paraquat @ 1,500 ppm at 135 DAS (D₇), paraquat @ 1,500 ppm at 150 DAS (D₈) and control (D₉). Observations, viz. growth parameters, yield-attributing characters and senescence parameters were recorded at 10 days after spraying and economics were worked out. The highest percentage of the senescence attributes, viz. percentage of of yellow leaves, yellow plants, dried leaves and leaf fall, was observed paraquat @ 1,500 ppm applied at 150 DAS. This was comparable with spraying of paraquat @ 1,500 ppm at 135 DAS and ethrel @ 2,500 ppm at 150 DAS during both years. Ethrel @ 2500 ppm at 150 DAS recorded the highest boll weight and more number of bolls/plant, resulting in significantly highest seed-cotton yield. The higher net income and the benefit: cost ratio were also recorded with the application of ethrel @ 2,500 ppm at 150 DAS.