Armillaria oytoyae is a natural condition of the site on which affected trees are growing. Perhaps the largest mushroom in the world, Armillaria consists of extensive fungal threads connected in the soil, primarily through Douglas-fir, grand fir and subalpine fir roots, but also occasionally through the roots of ponderosa pine and other species. The fungus can remain alive in dead woody material for decades, eventually affecting young trees as they develop. Armillaria girdles the trees by killing the root cambium and the root collar. Bark beetles often attack infected trees, speeding their demise.
Appearance Armillaria affects "pockets" of trees in a forest. The infected trees die and break off before they reach maturity. As the trees die, openings are created that make room for thickets of saplings. But the young trees never reach maturity, being infected by the root disease.
Management
If retaining timber value is a goal, the only long-term option is to convert the Armillaria-infested forest by planting with resistant species, such as western larch.
Armilllaria has been shaping Swan Valley forests for centuries. Trees killed by this root disease provide homes for cavity nesting birds, and the Armillaria thickets are good places for deer to hide their fawns.
