Development of optimal norms and timing of defoliation in fine-staple cotton (Gossypium barbadense L.) varieties

Abstract

The article scientifically substantiates the optimal timing and application rates of local defoliants SuyuqXMD and UzDEF on the fine-staple cotton variety “Termiz-202”. The research was conducted during 2018–2020 across three distinct soil-climatic conditions of the republic (Surkhandarya, Tashkent, and Samarkand regions). The results indicated that the most optimal timing for defoliation in fine-staple cotton is when 40–50% of the bolls are open on the plant. Under the hot and dry conditions of Surkhandarya, applying SuyuqXMD at 9.0 L/ha and UzDEF at 8.0 L/ha ensured leaf drop up to 90.3–91.5%. In the Tashkent region, where autumn temperatures are lower, the highest efficiency was recorded with SuyuqXMD at 10.0 L/ha and UzDEF at 9.0 L/ha, whereas in the Samarkand region, UzDEF at 9.0 L/ha performed best. Due to the defoliation measure, an additional yield of +3.1 to +4.3 c/ha was achieved across the regions, and the profitability rate increased by 11.5–14.4% compared to the control, enabling the mechanical harvesting of almost 90–95% of the total yield as premium industrial grades in the very first picking.