Annosus Root Rot

Fomes annosus (Fr.) Cke.

From: Field Guide to Diseases and Insect Pests of Idaho and Montana Forests, USDA Forest Service Northern Region, Publication Number R1-89-54

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

Distribution. – Range of hosts in Idaho and Montana, west of the Continental Divide.

Damage. – Annosus root rot occurs in trees of all ages. The fungus decays roots and colonizes 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 surf ace dark brown and the lower surf ace white to cream colored (fig. 71). 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 (fig. 72). 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 fleeks.

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.

Link to Table 2 – Comparison of Common Root Diseases

Link to Images in Forestry Images

References.

Anonymous. 1982. For. Insect & disease identification and management. USDA For. Serv.,Northern Region; Idaho Dept. of Lands, Insect and Disease Control; Montana Dept. of State Lands, Division of Forestry. 192 p.

Bega, R. V. 1978. Diseases of Pacific Coast conifers. USDA For. Serv. Ag. Hndbk. No. 521, 206 p.

Boyce, J. S. 1961. Forest Pathology. McGraw-Hill Book Co., New York, NY. 572 p.

Hepting, G. E. 1971. Diseases of forest and shade trees of the United States. USDA For.
Serv. Ag. Hndbk. No. 386, 658 p.

Smith, R. S., Jr., and D. Graham. 1975. Black stain root disease of conifers. USDA For. Serv., For. Pest Leaflet 145, 4 p.

Smith, R. S., Jr., and D. Graham. 1975. Black stain root disease of conifers. USDA For. Serv., For. Pest Leaflet 2086, 4 p.

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