Armillaria root disease is found throughout temperate and tropical regions of the world. In the continental United States, the disease has been reported in nearly every State. Hosts include hundreds of species of trees, shrubs, vines, and forbs growing in forests, along roadsides, and in cultivated areas.
The disease is caused by fungi, which live as parasites on living host tissue or as saprophytes on dead woody material. The fungus most often identified as causing the disease is Armillaria mellea (Vahl: Fr.) Kummer. Recent research, however, indicates that several different but closely related species are involved. Therefore, the generic term Armillaria is used to refer to this group.
As parasites, the fungi cause mortality, wood decay, and growth reduction. They infect and kill trees that have been already weakened by competition, other pests, or climatic factors. This type of activity occurs throughout the United States--especially in deciduous forests of the East. The fungi also infect healthy trees, either killing them outright or predisposing them to attacks by other fungi or insects.
Sometimes on conifers there is a large production of cones before dying. Mushrooms around the base are another sign that there are problems. Yellowing of the canopy visible once the disease takes hold.
