a root disease caused by Armillaria species —note 1. in colonized trees, the fungus forms bioluminescent mycelial fans in the inner bark of stems and roots, reddish brown to black rhizomorphs (common name shoestring root rot), and honey-colored mushroom sporocarps (common names honey fungus and honey mushroom) —note 2. many species of Armillaria are secondary pathogens, but some are serious primary pathogens that can attack, colonize, and kill apparently healthy trees or predispose trees to bark beetle attack —note 3. stumps or dead trees serve as root disease (infection) centers that can expand to cover several hectares This definition last updated 10/23/2008