Description:
<jats:title>Abstract</jats:title><jats:p><jats:italic>Ailanthus altissima</jats:italic> is an invasive alien species in Europe. Biological control of this tree species by <jats:italic>Verticillium nonalfalfae</jats:italic> is a potential alternative control approach. This study investigates host specificity, pathogenicity and transmission of <jats:italic>V</jats:italic>. <jats:italic>nonalfalfae</jats:italic> to neighbouring plants with root contact in mini‐ecosystems. <jats:italic>V</jats:italic>. <jats:italic>nonalfalfae</jats:italic> led to dieback of all inoculated <jats:italic>Ailanthus</jats:italic> trees. Furthermore, <jats:italic>V</jats:italic>. <jats:italic>nonalfalfae</jats:italic> was transmitted to neighbouring <jats:italic>Ailanthus</jats:italic> trees, causing wilt and dieback, and, in one case, to <jats:italic>Quercus petraea</jats:italic>, which did not display any disease symptoms. Lastly, <jats:italic>V</jats:italic>. <jats:italic>nonalfalfae</jats:italic> could not be detected in the soil, which suggests transmission via root contact.</jats:p>