Efficacy tests on commercial fungicides against ash dieback in vitro and by trunk injection

Ash dieback, caused by Hymenoscyphus pseudoalbidus Queloz et al. (anamorph Chalara fraxinea Kowalski), has emerged as a critical disease in urban areas and in the forests of many European countries. This study was conducted to evaluate six fungicides for their potential to control the disease. In vitro assays with different concentrations of the products against five different strains of the pathogen, illustrated that thiabendazole, propiconazole and allicin exhibited lower median lethal doses, procloraz completely killed half of the samples at higher concentrations, whereas copper sulphate and potassium phosphite were totally ineffective. Subsequently, the antifungal activities of the best three compounds were investigated in planta against H. pseudoalbidus by trunk injection. The rate of necroses development following artificial inoculation of 24 F. excelsior was significantly slowed down in the growing season by the treatment with thiabendazole and allicin. In the phenological phase and climatic conditions tested, and with the chosen formulation and injection method, propiconazole injections were impracticable. The results of this study, along with some technical suggestions for application in the field, support the idea of using organic and chemical endotherapic products to combat ash dieback symptoms in Fraxinus spp., with the safe and very low impact method of trunk injection.