Armillaria Root Rot
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Hagle, S.K; S. Tunnock; K.E. Gibson; and C.J. Gilligan. 1987. Field Guide to Diseases and Insect Pests of Idaho and Montana Forests. U.S. Department of Agriculture, Forest Service. State and Private Forestry, Northern Region. Missoula, Montana. Reprint 1990. Publication Number R1-89-54.
Contents |
Hosts
Primary hosts are Douglas-fir and grand fir although all conifers may be attacked, particularly at ages less than 30 years.
Distribution
Range of hosts in Idaho and Montana, especially west of the Continental Divide.
Damage
Decays roots and kills cambium in roots and root collar. Causes mortality in groups and scattered, individual trees (fig. 59). Infected trees are often attacked by bark beetles.
Identification
Trees infected with Armillaria have typical root disease crown symptoms. Resinosus often is extensive on and throughout the bark of the root collar (fig. 64). The most diagnostic feature is the thick, fan-shaped mat of white mycelium (fig. 65) in the cambium of roots and root crown. Other signs of the fungus include rhizomorphs on the outside of infected roots and honey-colored mushrooms. The mushrooms may be produced at the base of infected trees during late summer or early autumn. The decay is white to yellow and stringy or spongy, sometimes with fine, black lines traversing the decayed wood (zone lines).
Similar damages
Laminated root rot causes basal resinosus as well but thick, white mycelium fans are not produced in this disease.
Comparison of Common Root Diseases
| Fungus | Hosts | Basal Resinosus | Decay | Other Distinguishing Characteristics |
|---|---|---|---|---|
| Armillaria ostoyae | 1. DG, GF, saping pines 2. Other conifers | Yes | White or yellowish, stringy with black zone line and rhizomorphs | Thick fan-shaped felts of white mycelium in cambium |
| Phellinus wirii | 1. DF, GF
2. Other conifers | Yes | Laminated, separating at annual rings, pitted with pinhead-sized holes | Cream-colored mycelium on outer bark of roots and root collar under duff. Cinnamon-colored mycelium often in bark cracks with cream cycelium. |
| Phaeolus schweinitzii | 1. DF
2. Other conifers | No | Brown cubical rot of root and butt heartwood | Small roots with red-brown resinous heart; galled roots; large brown, velvety conks with green or brown pore layer on underside produced on ground or base of tree. |
| Fomes annosus | 1. DF, GF
2. SAF, WH, PP, WRC, WWP | No | White or yellowish, stringy to somewhat laminate. White pockets with black flects sometimes present | Conks shelving or flat on sides in hollow stumps. Conks have brown upper surface and white lower, pored surface with brown, non-pored margin. Cream-colored mounds (button conks) below duff on seedlings. |
| Ceratocystis wageneri | 1. PP,LPP, DF
2. ? | No | No decay produced | Black or brown stain in sapwood follows annual rings. |
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.
- Kimmey, J. W. 1964. Heartrots of western hemlock. USDA For. Serv., For. Pest Leaflet 90, 7 p.
- Williams, R. W., C. G. Shaw, III, P. M. Wargo, and W. H. Sites. 1986. Armillaria root disease. USDA For. Serv., For. Ins. & Dis. Leaflet 78, 8 p.
