Nanoemulsion of Apium graveolens essential oil as a natural pre-emergent herbicide

Essential oils (EOs) are recognized for their potential as environmentally compatible alternatives to synthetic herbicides, often associated with a reduced risk of resistance development. However, their practical application faces challenges such as volatility and inconsistent efficacy. To address these limitations and enhance herbicidal potential, nanoemulsions (NEms) of Apium graveolens L. EO (celery) were formulated and assessed for their efficacy against Phalaris minor Retz. biotypes resistant (R) and sensitive (S) to ALS and ACCase-inhibiting herbicides, as well as Avena ludoviciana Durieu. The EO of A. graveolens had 37 compounds, with limonene (76.95%) as the main one. In the Petri plate bioassay emulsion of A. graveolens EO completely inhibited the germination of R and S P. minor biotypes and A. ludoviciana at 0.1%w/w. The individual components, R (+) limonene, S (-) limonene and their binary mixtures were less effective and reduced the germination of R and S P. Minor biotype and A. ludoviciana at comparatively higher concentrations. Individual components at concentration of 3 to 4%w/w were also toxic to Triticum aestivum. NEm of effective EO concentrations were fabricated by high frequency ultrasonic method and a phase diagram was mapped. The physicochemical properties indicated the formation of isotropic oil-in-water NEm. Transmission electron microscopy (TEM) and Dynamic Light scattering (DLS) studies indicated spherical nature of droplets with an average size > 21 nm. The prepared formulations were stable to storage as well as external forces. Emulsion and NEms each prepared at 0.05 and 0.1% w/w. A. graveolens EO concentrations completely inhibited the germination of R and S P. minor biotypes and A. ludoviciana by altering the physiological processes such as reduction in seed imbibition by 20% to 40% and causing up to a 13% increase in membrane leakage, without having adverse effects on T. aestivum.