Mistletoe on urban trees in the city of Vienna, Austria

A study of mistletoe on urban trees was conducted in Vienna, Austria, with the aim to determine the degree of mistletoe infection, and to identify host species that are highly susceptible or alternatively, resistant to mistletoe parasitism. At the same time, the dependence of mistletoe (Loranthus europaeus L; Viscum album L) occurrence on various factors was investigated. For this purpose, the tree cadastre of the city of Vienna was evaluated (the record is about 213,841 trees) and the Botanic Garden of the University of Vienna was visited. New host trees, not known in the literature, were described for the first time. The apparent spreading of mistletoes cannot be traced to a single factor; several are important and interacting. It could be shown that the presence of mistletoe in cities is closely related to the species of host tree, the location, the growing density of the trees, the age of the trees, as well as tree height. The host trees often showed marked adaptation of native tree species to mistletoe (i.e., fewer infections) and significant infection in introduced tree species. In some species, certain cultivars may be resistant or less susceptible to mistletoe than others. Among the damage or diseases observed on trees infected by mistletoe, bark damage occurred most frequently. Determining the distribution of mistletoe and the underlying factors is of great importance for green space management in cities, especially in relation to climate change.