ABSTRACTArmillaria mellea, A. ostoyaeandA. bulbosa, but notA. tabescens, infected some of the heavily suppressed oaks that had been inoculated, whereas onlyA. melleainfected subdominant oaks. The same three species also infected suppressed Scots pines, but onlyA. ostoyaeinfected subdominant ones. Infections in stump roots of oak inoculated withA. mellea, A. ostoyae, A. bulbosaandA. tabescenswere small unless roots had been weakened by severing; intact stump roots of pine were colonized more extensively than those of oak by the first three species.