Effect of Different Defoliants and Time of Application on Defoliation Percentage and Boll Opening Percentage in High Density Cotton (Gossypium hirsutum L.)

Aims: To evaluate the time and type of chemical defoliants to improve the mechanical and manual picking of high density cotton CO 17 in terms of higher defoliation and increase boll opening percentage.

Study Design: The study was performed in split plot design with seven treatments and four replications.

Place and Duration of Study: This field study was carried out in Department of Crop Physiology TNAU, Coimbatore during September 2019 to January 2020.

Methodology: Three time of defoliants application (120 Days After Sowing (DAS), 127 DAS and 134 DAS) for main plot and seven treatment levels of Control, 2, 4 D (0.5%), Ethephon (0.5%), Ethephon (0.5%) + TIBA (450 ppm), Sodium chlorate (0.9%), 6-BAP (0.1%), Thidiazuron + Diuron (0.03%) for sub plot.

Results: Defoliation percentage was significantly enhanced from 4 days after defoliants spray. Boll opening percentage also increased with defoliants spray when compared to control plants. Although a significant effect was observed on SPAD value, NDVI value and seed cotton yield.

Conclusion: From this study, application of Thidiazuron + Diuron (0.03%) and Sodium chlorate (0.9%) had significantly positive effect in per cent defoliation and boll opening percentage and it will work better in young cotton plants compare to mature one.