Influence of Heat Units on Defoliation, Physiology and Yield of Cotton during Defoliants Application

Aims: A study was conducted to determine the effect of temperature on defoliation process, physiology and yield of cotton during defoliants application.

Study Design: The experiment was laid out in split-plot design with four replications.

Place and Duration of Study: Field experiment was conducted at Department of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore during 2018 to 2019.

Methodology: The main plot comprised of three stage of defoliants spray (120 DAS, 127 DAS and 134 DAS) and the sub-plots were seven defoliant treatments (Control, 2, 4 D (0.5%), Ethephon (0.5%), Ethephon (0.5%) + Triiodbenzoic acid (TIBA) (450 ppm), Sodium chlorate (0.9%), 6 benzylaminopurine (BAP) (0.1%), Thidiazuron + Diuron (0.03%).

Results: After 15 days of defoliants spray, Thidiazuron + Diuron (0.03 %) recorded highest defoliation percentage (99.3, 98.1 and 96.8%) followed by Sodium chlorate (0.9 %) (91.9, 94.6 and 93.6%) at three different stage of defoliants spray. Although a significant effect was observed on chlorophyll index value (SPAD) due to the favorable weather condition like minimum temperature of 14.3, 16.9 and 19.3°C and maximum average temperature of 30.8, 31.8 and 33.23°C (120, 127 and 134 DAS respectively) during defoliants spray to 15 days after defoliants spray. Sodium chlorate (0.9%) and 6-BAP (0.1%) recorded higher (95.8 and 95.4) per cent boll opening at 120 DAS when comparing to 127 DAS and 134 DAS. Heat units accumulated during defoliants spray to 15 days after defoliants spray was 113.54, 140.52 and 169.57°C days (120, 127 and 134 DAS respectively).

Conclusion: Therefore, the minimum and maximum temperatures of 14.3 and 33.3°C, respectively conducive for inducing defoliation process and boll opening in cotton.