Infection process

In general, Armillaria infection tends to be more successful in susceptible hosts that are weakened, stressed, and/or maladapted to the current conditions on the site. After successful penetration through the bark, pathogenic Armillaria spp. produce mycelial fans in the vascular cambium beneath the bark of living trees, and these mycelial fans begin to degrade cellular components of the woody host. However, saprotrophic Armillaria spp. can also produce mycelial fans on dead trees or other woody materials. As infection progresses, roots and/or basal boles can be partially or fully girdled, and the tree continues to lose vigor, which also increases susceptibility to other pests and environmental stresses. After the host tissue dies, Armillaria is sustained by deriving nutrients obtained by colonization and degradation of dead wood and other organic matter. Armillaria is also capable of causing wood rot, such as heart rot, that can weaken the structural integrity of the basal bole and/or lateral roots. Trees with such wood rot represent hazard trees that are susceptible to structural failure and/ or wind throw, which can threaten life, limb, and property.