The wood of the root will break apart easily between the annual rings and will be heavily pitted on both sides. An infected stand will be riddled with downed trees lying in different directions. Conifers are the favorite food of Armillaria root rot, although it will also attack hardwoods and shrubs. Above ground symptoms include a white fungal growth between the bark and the wood at the base of infected trees. Two different strains of the fungus that causes Annosus Root and Butt rot are found in the Northwest.
Decayed wood contains white mycelium and small black flecks about the size of rice grains.
R-6 Cooperative Programs and Washington State University Cooperative Extension.