The efficiency of Thymus vulgaris, Lavandula angustifolia, and Cupressus sempervirens essential oils in suppression of Hymenoscyphus fraxineus on Fraxinus angustifolia seedlings

Due to intense ash dieback, this research tested the bioactivity of Thymus vulgaris, Lavandula angustifolia, and Cupressus sempervirens essential oils (EO) against Hymenoscyphus fraxineus. In vitro testing showed that EOs had a pronounced fungitoxic effect on H. fraxineus. The most effective EO was extracted from T. vulgaris, while EOs obtained from L. angustifolia and C. sempervirens were less effective and showed the same effect. At a concentration of 1%, all tested EOs inhibited mycelial growth, while 0.01% and 0.1% concentrations of EO extracted from T. vulgaris also inhibited the growth of H. fraxineus. The in planta test of EO extracted from T. vulgaris conducted on three-year-old Fraxinus angustifolia seedlings showed a reduction in the size of necrotic lesions and a better crown condition compared to untreated seedlings. This research demonstrates, for the first time, the efficiency of EOs in suppressing ash dieback making a path for the development of new biological protection measures against H. fraxineus.