Technical Abstract: Invasive species are often assumed to have escaped from specialist enemies. A few studies support this but only in the context of species-level specificity, and not ecotype-specificity, of mostly insect herbivores/parasites. Here we compare the ecotype-specificity of soil-borne pathogens (Pythium spp.) associated with an invasive tree (Prunus serotina) in its native vs. Non-native ranges. Host ecotype had little effect on measures of pathogenic activity when interacting with Pythium from the native range. In contrast, pathogenic responses varied between host ecotypes when interacting with Pythium from the non-native range suggesting a greater level of host-specificity by the pathogens from the non-native than native ranges. Encountering more specialized enemies in the non-native than native ranges is counter to general invasion ecology predictions; however, functionally these Pythium isolates are less virulent than those in the native range. Further empirical evidence is necessary to interpret the importance of different types of enemy host-specificity and virulence to determine if enemy virulence is linked to levels of host-specificity. This is necessary to evaluate the efficacy of organisms as potential biological control agents of foreign (classical biological control) and endemic origin and improve our basic understanding of invasion biology and the evolution of host-pathogen interactions.