Programming flumetralin delivery with polyurea nanocapsules for durable tobacco bud suppression and mitigated aquatic toxicity

: Flumetralin is a widely used plant growth regulator for tobacco axillary bud control, but conventional formulations often suffer from rapid release, insufficient persistence, low utilization efficiency, and potential ecological risks. In this study, a polyurea-based flumetralin nanocapsule system (Flu@PU NC) was developed through interfacial polymerization to improve the delivery behavior, biological efficacy, and environmental safety of flumetralin. The prepared nanocapsules exhibited a well-defined spherical core–shell structure, high encapsulation efficiency, and good colloidal stability. Structural characterization confirmed the successful encapsulation of flumetralin within the polyurea matrix, while release and photostability studies demonstrated sustained-release behavior and improved resistance to photodegradation. After interfacial optimization with a suitable surfactant, the nanocapsule formulation showed enhanced wetting, spreading, and adhesion on tobacco leaves, which favored active ingredient retention at target sites. Bioassays further indicated that Flu@PU NC improved the inhibition of tobacco axillary bud growth compared with conventional formulations. In addition, aquatic toxicity assessment using zebrafish revealed that the nanocapsule formulation reduced acute toxicity relative to commercial formulations. These results suggest that nanocapsule-enabled delivery can simultaneously improve the persistence, efficacy, and safety of plant growth regulators, providing a promising strategy for sustainable crop management.