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

<i>Sclerotinia sclerotiorum</i> 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) (<i>Rosmarinus officinalis</i>, <i>R. officinalis</i> var. <i>verbenone</i>, <i>Lavandula hybrida</i>, <i>Origanum majorana</i>, and <i>Thymus vulgaris</i>) 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. <i>T. vulgaris</i> EO completely inhibited <i>S. sclerotiorum</i> mycelial growth at all tested concentrations. <i>R. officinalis</i>, <i>L. hybrida</i>, and <i>O. majorana</i> also showed full inhibition at 1% and 10%, while <i>R. officinalis</i> var. <i>verbenone</i> achieved 80-100% inhibition. <i>R. officinalis</i> had the least phytotoxic effects, with only a minimal effect on chard at 1%. <i>R. officinalis</i> var. <i>verbenone</i> caused low/moderate phytotoxicity in lettuce and chard but had no toxic effect on tomato. <i>L. hybrida</i> and <i>O. majorana</i> had moderate to low effects, while <i>T. vulgaris</i> 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.