In Vitro Assessment of Essential Oils as Sustainable Antifungal Agents Against Sclerotinia sclerotiorum Causing Lettuce Drop

Sclerotinia sclerotiorum is a soilborne fungal pathogen, and it is a major threat to lettuce production, causing lettuce drop. This study evaluated the antifungal effectiveness of five essential oils (EOs) (Rosmarinus officinalis, R. officinalis var. verbenone, Lavandula hybrida, Origanum majorana, and Thymus vulgaris) at 0.1%, 1%, and 10%, along with their phytotoxic effect in the field on three different crops (lettuce, tomato, and chard) following foliar application. T. vulgaris EO completely inhibited S. sclerotiorum mycelial growth at all tested concentrations. R. officinalis, L. hybrida, and O. majorana also showed full inhibition at 1% and 10%, while R. officinalis var. verbenone achieved 80–100% inhibition. R. officinalis had the least phytotoxic effects, with only a minimal effect on chard at 1%. R. officinalis var. verbenone caused low/moderate phytotoxicity in lettuce and chard but had no toxic effect on tomato. L. hybrida and O. majorana had moderate to low effects, while T. vulgaris was the most phytotoxic, significantly affecting lettuce and tomato at 1%. Further field trials are needed to define EO application protocols toward sustainable lettuce drop management without risks of phytotoxicity