An integrated approach to control the introduced forest pathogen Heterobasidion irregulare in Europe

The North American fungal pathogen Heterobasidion irregulare is currently distributed in pine and oak stands along 103 km of coastline west of Rome, Italy. This paper reviews and expands the knowledge on impacts, pathways of introduction and invasion, factors driving the invasion and on the dispersal abilities of this pathogen in Italy. Further, an integrated disease management program to minimize the spread of the fungus in Europe is suggested, based both on the published literature and on new findings reported here. Observational and genetic evidence support a single introduction through infected wood during World War II, and a subsequent invasion through spore dispersal. Experimental evidence suggests transmission potential of the pathogen rather than hypersusceptibility of native hosts is the major determinant of invasion. The current range of H. irregulare is too vast to suggest eradication, however, we recommend minimizing the risk of spread of H. irregulare outside the zone of infestation while reducing the magnitude of infestations within its current range. We provide evidence suggesting the most cost-effective management approach hinges on preventing the saprobic establishment of the fungus in stumps in a 'buffer' area surrounding the current zone of infestation.