Biodegradable Carboxymethyl Chitosan/Polyvinyl Alcohol Hymexazol-Loaded Mulch Film for Soybean Root Rot Control

Soybean root rot is an important disease that has affected soybean crops in recent years, but the available control methods still do not provide good protection for soybeans. In this study, three biodegradable mulch films (HML@CMCS, HML@PVA, HML@CMCS/PVA) were prepared from carboxymethyl chitosan (CMCS) and polyvinyl alcohol (PVA), and hymexazol (HML) was loaded on them. The surface and cryofractured surface were compared via micromorphological observations using SEM, AFM, and 3D measurements. Mechanical, water barrier, and optical properties were compared between the different films, and the results showed that the composite film (HML@CMCS/PVA) had better tensile properties, lower water content (35%), and lower water solubility (28%), while water barrier properties were significantly improved. HML@CMCS/PVA also had better light transmission than commercial films (opacity at 600 nm of 1.92). Finally, the composite film was selected to study antifungal properties, soil degradability, and biosafety. The results showed that it exhibited significant inhibitory activity against Fusarium oxysporum and could effectively control soybean root rot, while degradation reached 58% after 7 d of soil burial, and the mortality of earthworms relative to the microplastics produced by the film within 7 d (23.33%) was much lower than that of the commercial film, demonstrating its excellent biosafety. This study provides a new approach for the on-farm management of soybean root rot and the reduction in soil microplastic pollution.