Annosus Root Rot
Fomes annosus (Fr.) Cke.

Hosts - Douglas-fir, ponderosa pine, and subalpine fir are killed. Roots of western redcedar are rotted. It causes a butt rot in western hemlock.

Damage - Annosus root rot occurs in trees of all ages. The fungus decays roots and colonized root collar cambium, killing trees. In true firs and western hemlock, the fungus often decays the butts of older trees for many years before causing tree death.

Identification - Trees with annosus root rot display typical root disease crown symptoms. Conks are perennial, woody to leathery, with the upper surface dark brown and the lower surface white to cream colored. Pores on the lower surface are very small. There is a rim of brown, non-pored tissue around the edge of the lower surface. Conks are produced in hollows within infected stumps or under the duff at the base of recently killed trees. Button conks-small, cream-colored mounds of corky fungus tissue-are sometimes found on the root collar of infected seedlings. If conks cannot be found, culturing of the fungus may be necessary for identification. Incipient decay appears as a light brown stain in the outer heartwood of lower stems or roots. Advanced decay is a white, stringy to somewhat laminate decay. In the most advanced stage, decayed wood may become wet and spongy with numerous small black flecks.

Similar damages - Armillaria root rot and laminated root rot cause similar crown symptoms to those of annosus root rot. Decay from these diseases is also superficially similar because all three cause white rot.

Management - Spores are present in the atmosphere and can be carried by the wind and infect fresh stumps. The fungus can also move to surrounding trees through root contact and grafts. Stand thinnings or damage to trees from logging operations can intensify annosus root rot problems. Avoid injuries to trees through logging activity. The fungus is able to survive in stumps for several decades. The treatment of stump surfaces with Borax has been practices to prevent spore infection.