The article describes the effect of defoliation on the fall of cotton leaves depending on the timing of topping and irrigation scheduling. When irrigating cotton, the irrigation scheduling of 65-70-60 and 70-75-65 Fc was selected, and for each irrigation scheduling, plant topping was carried out on 12-13 and 14-15 sympodial branches. The optimal rate of application of the defoliants UzDEF and PolyDEF on all treatments of the plant topping is specified.