Curative Treatment of Strawberry Gray Mold Caused by Botrytis cinerea Using Lavender Essential Oil

Lavender essential oil exhibits strong in vitro antimicrobial activity against Botrytis cinerea; however, its efficacy under field conditions remains inconsistent. This study evaluated the effectiveness of lavender essential oil (Lavandula angustifolia × latifolia ‘Vaucluse’) against gray mold in strawberry (Fragaria × ananassa cv. ‘Joly’) under natural field conditions. In vitro assays confirmed pronounced antifungal activity, with a disc diffusion inhibition zone of 10.33 mm and minimum inhibitory concentrations of MIC₅₀ = 0.29 mg mL⁻¹ and MIC₉₀ = 0.38 mg mL⁻¹. Based on these results, field trials were conducted using a 10% (v/v) essential oil formulation applied either alone or as a curative treatment 24 h after inoculation with B. cinerea strain F-314. Despite strong in vitro efficacy, field application of lavender essential oil alone resulted in the highest gray mold incidence (53.9%), representing a 79% increase compared with untreated controls (30.1%) and a 108% increase relative to pathogen inoculation alone (25.9%). In contrast, curative application 24 h after pathogen inoculation produced the lowest disease incidence (13.7%), corresponding to a 55% reduction compared with untreated controls and a 47% reduction compared with pathogen-only treatment. The fourfold difference in disease incidence between essential oil application alone and curative treatment demonstrates that lavender essential oil can either exacerbate or suppress gray mold depending on application context. The increased disease incidence following essential oil application alone is likely attributable to phytotoxic stress and disruption of protective epiphytic microbiota, effects that were amplified by exceptionally high precipitation during the experimental period. Conversely, the efficacy of curative application may result from direct antimicrobial activity against established infections, reduced duration of phytotoxic exposure, and possible induction of host defense responses. These findings demonstrate that in vitro antimicrobial activity alone is insufficient to predict field performance and challenge the assumption that botanical antimicrobials effective in laboratory assays will necessarily confer disease protection when applied to plants. In strawberry gray mold management, lavender essential oil shows potential as a curative treatment but should not be applied in the absence of pathogen challenge, as this may increase disease susceptibility.