Crop growth scenario-based pH/temperature dual-responsive degradable polyurea nano/microcapsules: Smart pesticide delivery and sustainable control of Fusarium crown rot in wheat

Designing smart pesticide delivery systems in response to the environmental factors of disease occurrence is critical to achieving targeted pesticide delivery, improving effective pesticide utilization and reducing environmental pollution. Herein, we prepared a novel chemically degradable pH/temperature dual-responsive polyurea capsule (Pyr@PU). The Pyr@PU was based on the diamine cross-linking agent 2,2-diethoxypropane (DAKT) containing acetal groups unstable to acids and isophorone diisocyanate (IPDI), and the phase change material methyl myristate (melting point: 18°C) was used as the oil phase. Owing to the acetal structure in the capsular shell and methyl myristate in the core, Pyr@PU has excellent acidic pH responsiveness and temperature sensitivity. 95.0 % of the fungicidewas released within 48 h at a weakly acidic condition (pH = 5.0), and the fungicide release rate at 35°C was 3.6 and 10.4 times higher than that at 25°C and 15°C, respectively. Bioactivity assays showed a longer duration of Pyr@PU compared to the commercial emulsion (Pyr EC). The degradation rate of Pyr@PU microcapsules (Pyr@PU-Micro) (64.5 %) was significantly lower than Pyr EC (98.6 %) after 24-h UV irradiation. In the 96-h acute toxicity test, Pyr@PU-Micro (LC₅₀ = 0.695 mg·L⁻¹) exhibited a lower toxicity to zebrafish than the Pyr (LC₅₀ = 0.076 mg·L⁻¹), Pyr EC (LC₅₀ = 0.108 mg·L⁻¹), and commercialized microcapsules (Pyr CS) (LC₅₀ = 0.209 mg·L⁻¹). In summary, the new chemically degradable polyurea microcapsules improved the stability and duration of fungicide efficacy and provided a new solution for the effective control of Fusarium crown rot and the reduction of environmental pollution caused by microplastics.