Construction of Thermoresponsive Microcapsules for the Controlled Release of Thidiazuron to Improve Defoliation Effects

The successful defoliation of cotton leaves by using chemical defoliants is extremely important for the mechanical harvest of cotton, which can greatly reduce the impurity content of cotton. However, the defoliation effect is seriously affected by temperature. Cotton absorbs excessive defoliants at high temperatures, which causes the cotton leaves to be scorched without falling off. We have constructed a smart carrier system through thermoresponsive microcapsules, which can decrease the release of defoliants at high temperatures to avoid an excessive absorption of defoliants by plants so that the absorption of defoliant by the leaves has been maintained at an optimal level. A defoliant microcapsule (TDZ@PDA-g-PMEO2MA) was prepared by loading thidiazuron (TDZ, a widely used defoliant) in a carrier of polydopamine grafted with 2-(2-methoxyethoxy)­ethyl methacrylate through a simple physical adsorption process to study its defoliation effect, with a high loading ratio of 45.9%. The outer polymer brush of the microcapsules can collapse at a high temperature to reduce the release of TDZ, thereby preventing the scorched leaves caused by the excessive absorption of defoliants by cotton. Compared with the commercially available TDZ formula (wettable powder), the cotton defoliation ratio is increased by 51.1%, which shows a better defoliation effect. Thermoresponsive microcapsules reduce the excessive absorption of defoliants by cotton by reducing the release of defoliants, which greatly enhances the defoliation effect of cotton at high temperatures. The result provides a new idea for how to increase the defoliation ratio at a high temperature.