Tea polyphenol–iron nanocapsules for oxalic acid‐triggered delivery of n ‐butylidenephthalide: a biorational strategy against Sclerotium rolfsii

Abstract BACKGROUND Sclerotium rolfsii is a destructive soil‐borne fungal pathogen distributed worldwide. Although n ‐butylidenephthalide (BP) exhibits strong inhibitory activity against S. rolfsii , its agricultural application is hampered by high volatility and poor water solubility. RESULTS To address these barriers, a pathogen‐triggered delivery system was engineered using tea polyphenol–iron nanocapsules (TP@Fe NCs). The 277 nm core‐shell capsules exhibited enhanced thermal stability and specific responsiveness to S. rolfsii , discharging 86.0% of the cargo under 1.0 m m oxalic acid (OA). In vitro assays confirmed superior bioactivity, with TP@Fe NCs exhibiting a significantly lower median lethal concentration (LC 50 ) of 13.34 mg/L compared to 21.53 mg/L for free BP. In glasshouse trials against peanut southern blight, TP@Fe NCs (300 mg/L) achieved a curative efficacy of 74.68%, significantly outperforming free BP (51.30%). Crucially, the formulation demonstrated excellent biosafety. Peanut seedlings treated with 200–300 mg/L TP@Fe NCs showed no phytotoxicity, maintaining emergence rates of 92.69% and normal root/stem development. Furthermore, acute toxicity tests on zebrafish (4.2–5.0 mg/L) revealed that while 5.0 mg/L free BP caused 100% mortality within 48 h, TP@Fe NCs maintained a > 90% survival rate over 96 h. CONCLUSION This study presents a biorational strategy for precise fungal control and develops an expandable and efficient framework for implementing eco‐friendly nanopesticide systems toward sustainable agriculture. © 2026 Society of Chemical Industry.