Improved Stability and Phytotoxic Activity of Wedelia trilobata Essential Oil (EO)-Loaded Microemulsions (MEs)

The excessive use of synthetic herbicides necessitates the development of eco-friendly alternatives. Wedelia trilobata essential oil (EO) possesses significant herbicidal potential, but its practical application is hindered by poor physicochemical properties such as high volatility and low water solubility. This study addressed these limitations by formulating oil-in-water (O/W) microemulsions (MEs) containing W. trilobata EO and assessing their herbicidal potential against lettuce ( Lactuca sativa L.) as a target plant. The EO was rich in oxygenated monoterpenes (41.45%), with geraniol (23.21%) and (R)-(+)-citronellal (11.04%) as the main compounds. Physicochemical characterization confirmed the formation of stable, isotropic MEs (ME-1 and ME-2). Transmission electron microscopy (TEM) revealed uniformly distributed, non-spheroidal droplets with average sizes below 20 nm. The formulations exhibited excellent thermodynamic and mechanical stability over 180 days. In phytotoxicity assays, ME-2 with 80% water content demonstrated potent inhibitory effects on lettuce, reducing shoot and root growth by 80.12 and 92.08%, respectively. These results indicate that the ME system successfully preserves the intrinsic bioactivity of W. trilobata EO while enhancing its stability and bioavailability. Overall, the findings provide critical proof of concept for emulsifying W. trilobata EO into a commercially viable, water-based ME for effective, sustainable weed control.