本研究于2019-2020年开展了田间试验，研究DPC化控封顶时期和剂量对喷施脱叶催熟剂（50%噻苯•乙烯利悬浮剂，简称TE，2250 g hm^-2）前吐絮率（9月中下旬，药前吐絮率）及TE施用后14天脱叶性状和吐絮率的影响。结果表明，2019年（棉株长势相对正常）晚封顶（T3期，接近生理终止，白花以上节位约为5.0，较当地人工打顶晚7天）与早封顶（T1期，盛花期，较当地人工打顶早7天）和中期封顶（盛花期后7天，与当地人工打顶时间相同）相比，药前吐絮率显著降低5.9%-11.2%；高剂量DPC（270 g hm^-2）封顶与低（90 g hm^-2）、中（180 g hm^-2）剂量DPC封顶相比，药前吐絮率显著降低22.0%。2020年（棉株后期长势偏旺）T3期封顶的药前叶片数虽然少于T1期和T2期，但药后14天的残留叶片数较多，脱叶率较T1和T2期封顶降低23.2%-27.2%；高剂量DPC封顶的药前叶片数与中、低剂量DPC封顶相似，但药后14天的残留叶片数最多，脱叶率较低、中剂量DPC封顶降低15.0%-21.7%。此外，2020年晚封顶主要影响果枝叶片（包括主茎叶）的脱落，而高剂量DPC封顶对果枝叶（包括主茎叶）和营养枝叶片的脱落均有影响。综上，花铃期应用DPC进行化控封顶对棉花熟性和脱叶催熟效果有一定影响，且具体结果与植株生长状态有关。为避免延迟成熟和降低叶片对脱叶催熟剂的敏感性，DPC化控封顶时间不宜过晚，也不宜采用高剂量DPC进行封顶。在黄河流域棉区，建议于盛花期~盛花期后7天左右（当地常年人工打顶时间）应用90-180 g hm^-2 DPC进行化控封顶。

棉花的脱叶催熟技术在机械收获中必不可少，尤其是在华北平原，由于热量资源不足，导致收获时残留绿叶和未开裂棉铃的比例较大，棉花机械收获受到限制。确定棉花脱叶催熟剂最佳用量，同时最大程度地减少产量和品质的损失至关重要。本文主要研究一种新型脱叶催熟剂-欣噻利（XSL，10%噻苯隆和40%乙烯利的复配剂）对棉花叶片和棉铃的空间分布，以及产量和品质的影响。本试验共设置了四个处理：不同的XSL剂量（1800和2700 mL ha^-1），应用两次（分为两次应用，每次1350 mL ha^-1）和无XSL（清水）对照。该大田试验于2016-2017年在中国河北进行。结果表明：与清水对照相比，所有脱叶催熟处理均未显著影响棉花的产量和纤维品质。两年数据显示，2700 mL ha^-1 XSL一次性喷施的棉花吐絮率比清水对照高13.5％，而其他两个处理均未达到显著水平。三个XSL处理的脱叶率之间没有显著差异，但平均比清水对照高42.2％。年份对XSL应用效果较为显著，表明气候因素会影响XSL的应用。我们得出的结论是，在黄河流域棉区使用XSL的最佳剂量为2700 mL ha^-1，而且无需分成两次应用。我们的结果将促进棉花机械化收获并降低棉花生产的人工成本。

Timing of harvest is critical for mechanical picking in cotton production, especially in those regions with double cropping system. Appropriate and safe harvest aids will improve timing and facilitate harvest of cotton in the double cropping system. Three defoliants (dimethipin, thidiazuron, and thidiazuron-diuron) and one boll opener (ethephon) were included in this research. They were evaluated for their effects on defoliation, boll opening, seedcotton yield, seed quality, and fiber quality of field grown cotton when used alone or as a mixture in 2009 and 2010. Defoliation and/or boll opening were increased by all three defoliants and ethephon, especially by mixtures of a defoliant and ethephon. First harvest of seedcotton was significantly increased with defoliant-ethephon mixtures. No significant adverse effects were observed on boll weight, lint percentage, seed quality, and fiber properties. It was estimated that tank mixes of ethephon and one of the three defoliants can improve the adjusted gross revenue. Boll opening can be used as an alternative indicator for the adjusted gross revenue, because, it was linearly and positively correlated with the relative adjusted gross revenue and convenient in measurements. Wheat seedling growth was not affected by thidiazuron, whereas its seedling emergence, root dry weight, relative water content, and electrolyte leakage were adversely affected by dimethipin and thidiazurondiuron when concentration was above 340 and 100 g (a.i.) ha-1, respectively. 90% defoliation and 80% boll opening were observed with the high rate of thidiazuron-ethephon mixture, but no adverse effects on winter wheat. The results suggested that tank mixes of ethephon with thidiazuron can be used effectively and safely in the cotton-winter wheat double cropping system to improve yield without adverse effects on seed quality and fiber quality.