Controlled Release of Spirotetramat Using Starch–Chitosan–Alginate-Encapsulation

This study was intended to develop an environment-friendly controlled release system for spirotetramat in an alginate matrix. Four formulations, starch–chitosan–calcium alginate (SCCA), starch–calcium alginate (SCA), chitosan–calcium alginate (CCA), and calcium alginate (CA) complex gel beads, were prepared by the extrusion–exogenous gelation method. The properties of the formulations were studied. The results showed that the release behaviors of the formulations in water could be well described by the logistic model, and the release occurred through Fickian diffusion. Among the four formulations, SCCA showed the highest entrapment efficiency, drug loading and the slowest release rate. Degradation studies revealed that the SCCA formulation exhibited an obvious slower degradation rate of spirotetramat in soils than the commercially available formulation. The estimated half-life of the SCCA formulation was 2.31, 3.25, and 4.51 days in waterloggogenic paddy soil, purplish soil, and montmorillonite, respectively, when the soils were moistened to 60% of its dry weight. This study provided a possible approach to prolong the duration of spirotetramat and to reduce environmental contamination.