Armillaria (Fr.) Staude is a widely distributed fungal genus comprising approximately 40 species (Volk and Burdsall 1995) that display diverse ecological behaviors ranging from beneficial saprobe to virulent pathogen. Armillaria solidipes (formerly A. ostoyae; Burdsall and Volk 2008; pending vote to conserve A. ostoyae; Redhead et al. 2011), one of the causal agents of Armillaria root disease, is a virulent primary pathogen with a broad host range in northern temperate latitudes (Kile et al. 1991). This fungal pathogen attacks sapwood as mycelial fans under the bark, and grows between trees as rhizomorphs. The pathogen causes a white rot of infected wood and is responsible for reduced forest yields as a result of direct tree mortality and non-lethal cryptic infections (Cruickshank et al. 2011).