Balancing mepiquat chloride and harvest aid applications for optimal cotton yield and defoliation in mechanical harvesting systems

Mepiquat chloride (MC) and chemical harvest aids are key tools for managing cotton growth and facilitating mechanical harvesting, yet their combined effects on yield and defoliation efficiency remain underexplored. This study investigated the effects of different dosages of MC on cotton plant architecture, maturity, and leaf traits, as well as its interaction with harvest aids. Field experiments were conducted in Xinjiang, China, in 2022 and 2023, with five MC treatments (66, 273, 480, 687, and 894 g·ha −1 ) during June to mid-August, and a combination of 10 % thidiazuron and 40 % ethephon was applied in September, with water as the control. Results showed that MC reduced plant height, while accelerating boll opening, particularly in heat-limited conditions. Harvest aid application increased boll opening by 18.0 % and seed cotton yield by 6.6 % compared to the control. High MC doses (894 g·ha −1 ) delayed defoliation due to thicker palisade tissues. Thus, optimal MC dosing (480 −687 g·ha −1 ) balanced boll maturation and defoliation efficiency, ensuring stable yields and high-quality machine harvesting. These results provide actionable insights for farmers to optimize MC use under varying environmental conditions, enhancing cotton production efficiency and mechanization. • Optimal mepiquat chloride (MC) dose promotes cotton structure, boosting boll opening and yield. • The use of MC can also effectively reduce the number of leaves per unit area before defoliant spraying. • Excessive doses of MC probably reduced cotton defoliation by affecting leaf anatomy structure change of the leaves.