Thermoresponsive controlled-release fluazinam microcapsules for improved efficacy and crop safety

Fluazinam is a broad-spectrum fungicide and acaricide, but its field performance is limited by temperature sensitivity and phytotoxicity. To overcome these challenges, a thermoresponsive nano-formulation (Flu@TRNP) was developed by encapsulating fluazinam in a poly(N-isopropylacrylamide-styrene) copolymer matrix via emulsion polymerization.

The microcapsules exhibited uniform spherical morphology (mean diameter: 3.4 μm), high encapsulation efficiency (75.3%), and temperature-dependent release governed by the polymer lower critical solution temperature (~32 °C). Below this temperature, release was almost complete, whereas above it, polymer shrinkage slowed diffusion and enabled sustained release. Flu@TRNP displayed significantly lower contact angles on leaf surfaces compared with commercial fluazinam, indicating improved wettability. Bioassays showed enhanced acaricidal activity against Tetranychus urticae, with median lethal concentration (LC₅₀) values reduced by up to 25% at 35 °C. Antifungal tests against Phytophthora infestans confirmed greater inhibition at 20 °C. Field trials demonstrated comparable or superior disease control efficacy at reduced or standard doses. Pot experiments under heat stress (40 °C) indicated lower phytotoxicity on cowpea and potato compared with the commercial formulation.

These results demonstrate that the thermoresponsive microcapsule formulation improves bioefficacy and crop safety while reducing the risk of phytotoxicity under fluctuating environmental conditions. © 2025 Society of Chemical Industry.