Lemon Oil-Loaded Ionic Liquid Nanoemulsions as a Sustainable Platform for Plant-Parasitic Nematode Management

Plant-parasitic nematodes (PPNs), particularly Meloidogyne enterolobii, pose a severe threat to global agriculture, necessitating the development of sustainable and highly effective management alternatives. Herein, we report the rational design, physicochemical characterisation, and nematicidal evaluation of lemon oil-loaded ionic liquid nanoemulsions. Three distinct ionic liquids (ILs)—1,3-Dimethylimidazolium acetate ([DMIM][OAc]), 1,3-Dimethylimidazolium chloride ([DMIM][Cl]), and 1-Methylimidazolium acetate ([MIM][OAc])—were integrated into oil-in-water nanoemulsions to assess their structural influence on formulation stability and bioactivity. The formulated ionic liquid nanoemulsions (IL-NEs) exhibited excellent colloidal properties, characterised by monodisperse nanometric droplets (18.13–24.42 nm, polydispersity index (PDI) < 0.4) and stable pH profiles with no visible phase separation over 120 days under the tested storage conditions. In vitro bioassays against M. enterolobii revealed a distinct structure–activity relationship (SAR) driven by the IL cation-anion composition, alongside strong concentration- and time-dependent efficacy. The [MIM][OAc]-based formulation demonstrated superior nematicidal performance, achieving the lowest terminal LC50 (0.23% at 20 h) and the most rapid mortality kinetics (LT50 of 7.63 h at 5.0%). Microscopic observations revealed marked morphological alterations, including internal structural damage and disruption of the integument. These findings unequivocally highlight the potential of structurally tunable IL-NEs as a potent, sustainable delivery platform for essential oil-based biopesticides in modern crop protection.