Figure 216. Cryptosphaeria colonizes sapwood and cambium.
Symptoms/Signs: Young infections and canker margins are orange to light brown.
The cankers are long (3 meters or more) and narrow (2-10 centimeters
wide), appearing as grayish depressions in the bark, with callus
ridges forming at the edge. Dead bark adheres to the canker face.
Inner bark is black and sooty with obvious fibers and small, light-colored
flecks (<2 mm). Light orange, tiny asexual fruiting bodies may
form near the edge of the canker. Clusters of black, flask-shaped
sexual fruiting bodies (perithecia) develop beneath bark dead for
more than 1 year. Cryptosphaeria ligniota also causes stain
in the sapwood and heartwood and causes a yellow-brown, mottled
decay.
Biology: Spores of C. ligniota
are released during wet weather and infect fresh wounds in the inner
bark and wood. The fungus eventually colonizes sapwood and heartwood,
causing discoloration and decay, before penetrating the bark and
causing a canker. Brown, mottled decay develops in the central part
of the column of discolored wood. Mortality occurs not from bark
necrosis as it may seem, but because the pathogen kills a large
volume of sapwood.
Effects: Trees up to 15 centimeters d.b.h.
may be killed within 3 years, with older trees taking longer to
girdle. Branch cankers are often found on large trees, where they
girdle the branch and enlarge onto the trunk. The decay associated
with the canker predisposes infected trees to wind breakage.
Similar Insects and Diseases: Bark that
has been dead for more than 1 year from C. ligniota is
black, stringy, and sooty-like, similar to sooty bark
canker (Encoelia pruinosa). However, they are easy to distinguish,
because of the lenticular-shaped fruiting structures and barber
pole design of E. pruinosa, both lacking in a Cryptosphaeria
canker.