Pathogens of introduced trees: prospects for biological control

Diseases affecting invasive tree species are widespread and some are well-known. To date, however, pathogens have been little used in attempts to control spread of these trees. In this short review, a list of selected introduced tree species is used to demonstrate the pathogens that attack these plants both within and outside their native ranges. The focus is on tree species that are of introduced origin and are invasive in certain parts of Europe, including ash-leaved maple (Acer negundo L.), tree of heaven (Ailanthus altimissima (Mill.) Swingle), eucalypts (Eucalyptus spp.), black cherry (Prunus serotina Ehrh.), red oak (Quercus rubra L.), Siberian elm (Ulmus pumila L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and Sitka spruce (Picea sitchensis (Bong.) Carr.). A range of specific and non-specific diseases for each species is reviewed with a view to assessing the use of these organisms in control and management of problematic tree species. Caution must be applied, however, as many pathogens are not host specific; moreover, predicting the behaviour of pathogens introduced from the native areas where the trees evolved is very difficult.