Armillaria root disease, Armillaria ostoyae,

				Photo not  available
Fig. 387 Mycelial fans of armillaria (A. sinapina) on trembling aspen.	Fig. 388 Young and old armillaria (A. sinapina) fruiting bodies. Note curved cap of younger fruiting bodies.	Fig. 389 Aspen trees expressing crown symptoms caused by armillaria.	Fig. 390 Young and old A. ostoyae fruiting bodies. Note curved cap of younger fruiting bodies.	Fig. 391 Cross-sectional view of advanced armillaria decay on aspen.

Distribution: A. ostoyae is present south of 52 degrees to 53 degrees (Prince George)
A. sinapina is present south of approximately 57 degrees North (Fort Nelson)
A. nabsnona is present in coast, southwestern B.C.

Host Susceptibility:  Armillaria ostoyae is found on all species, but infrequently on trembling aspen in south-central BC. A. sinapina is found on all species. A. nabsnona is most frequently found on red alder, bigleaf maple, and less frequently on black cottonwood.

What To Look For: Crown symptoms and mycelial fans at base of tree.

Signs & Symptoms: Crown symptoms include reduced top growth, premature defoliation, and leaf chlorosis. Trees can be affected either individually or in small groups defined as disease centres. Typically, centres include dead standing or fallen trees surrounded by dying trees. White, fan-shaped mycelial felts are present under the bark at the base of the tree. Mycelial fans in aspen are extensive and may extend over 1 m. In cottonwoods, they are thinner and less prominent. Blackening of the bark and lesions up to 1 m in length also appear at the butt. Black, shoe-string-like rhizomorphs are common on the roots, between the wood and bark and in surrounding soil. Rhizomorph widths range from 1 mm to 1 cm and can reach lengths of 1 m. A. ostoyae rhizomorphs are fewer in number and are branched in pairs. A. sinapina rhizomorphs are more abundant and branch in singlets off the main string. Rhizomorphs are rare in A. nabsnona-infected trees.

Fruiting Bodies: Large clusters of mushrooms may appear on infected trees and stumps in late summer to mid-autumn. The mushrooms are cream to brown with a 5 to 10 cm wide cap and a conspicuous ring on the stem.

Decay: In incipient (early) decay, wood is faintly water-soaked and then becomes light brown. In advanced decay, wood is light yellow or white and soft, spongy, and soggy.

Damage: Overall, damage to broadleaves by armillaria root diseases is minor. It rarely causes mortality unless the trees are under stress. There have been recorded incidences of reduced height and diameter growth, root decay, and reduced levels of suckering elsewhere in North America.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated April 23, 2002