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Host: Aspen
 Symptoms/Signs:
Young cankers appear as slightly sunken areas with near normal
bark color. Dead bark eventually falls off and reveals the black,
sooty and crumbly inner bark diagnostic for this canker. Beneath
the inner bark is a distinctive, black, feather-like pattern on
the wood surface. The perennial cankers form a band of light gray
bark that remains attached at the margin of each annual zone of
expansion giving the tree a barber pole appearance. Gray to black
leathery cup-shaped fruiting bodies develop on the inner bark along
the canker margin. The wood beneath cankers is light gray.
Biology: The fungus infects trees through
wounds and invades the inner bark and cambium. Cankers develop rapidly,
extending as much as 1 m in length and 0.3 m in width in a year,
however, the mean annual extension is about 45 cm vertically and
16 cm horizontally. The cup-shaped fruiting bodies—apothecia—develop
on the surface of old dead inner bark and open when wet. Spores
are forcibly ejected and wind disseminated when moisture and temperature
conditions are favorable. These spores can cause new infections.
 Effects:
Encoelia pruinosa is considered the most lethal and
aggressive pathogen of aspen in the West because it can kill trees
of all sizes in 3 to 10 years; some mature trees have been observed
to die in 4 to 5 years. Sooty bark is found mainly on the larger
dominant and codominant trees older than 60 years, in the middle
elevational limits of aspen. Cankers are more common in stands disturbed
by partial cutting, construction, camper damage, or animal damage.
Similar Insects and Diseases: Cryptosphaeria
canker can also produce dead inner bark with a soot-like appearance.
However, Cryptosphaeria produces a long lens-shaped, light-colored
area, which lacks the barber pole design.
References: 38,
39, 44,
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