Chitosan/carboxylated multi-walled carbon nanotube nanohybrid for hymexazol delivery: synergistic antifungal mechanism, controlled release kinetics and enhanced control efficacy against Sclerotinia sclerotiorum.

Nano-enabled pesticide formulations have emerged as a promising strategy to enhance fungicide bioavailability, achieve controlled release, and minimize off-target effects in sustainable agriculture. A hymexazol-loaded chitosan/carboxylated multi-walled carbon nanotube nanohybrid (Hymexazol@CS/c-MWCNTs, HCC) was developed as a nano-pesticide formulation for the green control of Sclerotinia sclerotiorum (S. sclerotiorum) in rapeseed. Chitosan/carboxylated MWCNTs (CS/c-MWCNTs) were obtained by EDC/NHS-mediated amide coupling between chitosan and carboxylated MWCNTs, and HYM was loaded at a 5:5 (w/w) ratio, affording a loading efficiency of about 61.64% and a porous three-dimensional network favorable for pesticide encapsulation and release. The sustained release of HYM from HCC was pH/temperature responsive, well described by a first-order kinetic model (R2 > 0.90). Furthermore, HCC significantly improved HYM photostability under UV irradiation and reduced its leaching in soil columns. In vitro antifungal assays revealed that HCC exhibited the strongest inhibition. At 200 μg/mL, the inhibition rates of HCC against S. sclerotiorum mycelial growth were 96.07%, with EC50 values of 11.29 μg/mL. Relative electrical conductivity, propidium iodide staining and electron microscopy confirmed that HCC severely damaged the cell wall and membrane structure of hyphae, causing electrolyte leakage and collapse. Greenhouse pot experiments on rapeseed demonstrated that HCC achieved a control efficacy of 73.33% at 200 μg/mL, superior to free HYM (63.64%) and CS/c-MWCNTs (51.67%). These results indicate that HCC is a promising nano-pesticide platform combining high antifungal efficacy, controlled release and improved environmental safety and offers a perspective for developing sustainable agriculture.