Aspen trunk rot, Phellinus tremulae
 

Fig. 359 Fruiting body of Phellinus tremulae on aspen.	Fig. 360 Sterile fruiting bodies on aspen trees.	Fig. 361 Cross-sectional and longitudinal view of advanced decay in trembling aspen caused by Phellinus tremulae.

Distribution:  Common throughout the range of aspen in B.C. 

TREE SPECIES ATTACKED:  Trembling aspen is the major host.

WHAT TO LOOK FOR: Large, triangular-shaped, fruiting bodies (conks) on the stem. 

SIGNS & SYMPTOMS: FRUITING BODIES: The conks are perennial, triangular in longitudinal section, and can reach dimensions of 15 cm in height and 20 cm in width. The upper and lower surfaces slant upwards approximately 45 degrees. The upper conk surface is grayish black to black and deeply zoned. It will roughen and crack vertically with age. The lower surface is purplish-brown and porous. The rust-brown interior of the conk is filled with distinct tube layers that are streaked with white mycelium. The conk age can be determined from the number of tube layers. Fruiting bodies appear at branch stubs or wounds on living and dead standing trees, and on slash. Presence of fruiting bodies (even one) indicates that a considerable volume of the tree is decayed. Black, blind conks (sterile mycelial masses) formed at branch scars are an additional external indicator of aspen trunk rot. The fungus is spread via windborne spores that invade exposed dead tissues.

DECAY: This fungus causes a white heart rot. It often produces a long decay column that continues throughout most of the main stem, and the decay usually occurs more than 2 m above ground level. Distinguishing characteristics of the decay are thin black lines bordering decay columns, with the surrounding wood stained reddish-brown. In advanced stages of decay, the wood inside the zone lines becomes soft and yellow-white in colour with fine black zone lines running throughout. The decayed wood produces a wintergreen odour when cut.

DAMAGE: This is the most common and most damaging cause of stain and decay in trembling aspen in BC. It lowers wood value in the incipient stage of decay by causing a red-brown stain, and later becomes structurally damaging as a white heart rot. It is estimated to cause 90 to 95% of aspen wood yield loss in northeastern BC. Volume losses increase significantly with tree age, particularly in stands over 30 years old. This disease may vary considerably from one stand to another, with decay lowest in more thrifty trees, perhaps as a result of interclonal variations. Trees with conks should be considered hazardous.

SIMILAR DAMAGE: Decay and fruiting bodies of aspen trunk rot are very similar to hardwood trunk rot. However, the former is only found on aspen, while the latter occurs on other hardwoods.

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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 March 04, 2002