In Vitro Evaluation of Mediterranean Lamiaceae Essential Oils as Natural Herbicides for Sustainable Weed Management

Mediterranean aromatic plants are valuable sources of essential oils (EOs) with biological properties that hold promise for sustainable weed management. This study evaluated the phytotoxic activity of EOs from Thymus vulgaris L., Lavandula angustifolia Mill., and Salvia officinalis L. in vitro against key weed species common to Mediterranean agroecosystems. The EOs were tested at concentrations ranging from 0.125 to 1.50 µL mL−1, assessing their impact on seed germination and early seedling growth of Avena fatua L., Lolium rigidum Gaudin, Sonchus oleraceus L., and Amaranthus retroflexus L. Thyme EO, primarily composed of thymol and γ-terpinene, exhibited the strongest phytotoxic activity, completely inhibiting the germination of A. fatua, L. rigidum, and S. oleraceus at all concentrations tested. In contrast, A. retroflexus was the most resistant weed species, with germination fully inhibited only at concentrations ≥ 0.50 µL mL−1. Lavender EO, rich in linalool and linalyl anthranilate, demonstrated a more species-specific effect. It almost entirely suppressed the germination of S. oleraceus at all doses and inhibited germination of A. fatua and L. rigidum at concentrations ≥ 0.50 µL mL−1. Again, A. retroflexus was the most tolerant species, with complete inhibition occurring only at the highest concentrations applied. Sage EO, containing eucalyptol and thujone as its main constituents, was the least effective, fully inhibiting S. oleraceus germination at concentrations ≥ 1.00 µL mL−1, and L. rigidum at 1.50 µL mL−1. Seedling growth was highly sensitive to EO treatments, even when germination was not entirely suppressed. These results highlight the potential of Mediterranean Lamiaceae EOs as plant-derived bioherbicides for integrated weed management.