Mepiquat chloride (MC) application timing and plant spacing significantly influenced Bt cotton growth and yield parameters. MC application, irrespective of timing, reduced plant height, but the most pronounced effect was observed when sprayed at the squaring stage. This height reduction was associated with increased boll number per plant, particularly under high-density planting. Additionally, MC treatments resulted in heavier bolls compared to the control, especially in wider spacings. Seed cotton yield (SCY) was significantly impacted by the interaction of MC timing and plant spacing. The highest SCY was achieved with MC applied at squaring, particularly at closer spacing, demonstrating a substantial yield advantage over the control. Both MC timings enhanced SCY at closer spacings, whereas the control yielded best at medium densities. These findings indicate that MC application at the squaring stage is superior in reducing plant height, promoting boll development, and ultimately maximizing cotton yield, especially under high-density planting. Nevertheless, both MC timings can optimize cotton production, underscoring the critical role of tailored plant spacing for yield maximization. Future research should investigate the physiological mechanisms underpinning these responses and explore the potential of MC in conjunction with other agronomic practices to further enhance cotton productivity.
