Figure 199. Red rot fruiting body on the underside of a dead ponderosa pine branch.
Symptoms/Signs:Dichomitus squalens produces a flat fruiting body
on the underside of dead branches or stems with intact bark. The
pore surface is white when fresh and ages to yellow. The red rot
fungus causes a white pocket rot. Like other wood decays, it has
two distinct stages: incipient and advanced.
The incipient stage is characterized by a reddish-brown discoloration
of the affected wood, unaccompanied by any obvious changes in structure
or strength. The advanced stage is characterized by small, often
poorly defined, white pockets in the discolored wood, accompanied
by progressive changes in structure and reduction in strength. As
decay progresses, the pockets become more and more numerous until
they merge and give the affected wood the appearance of a fibrous
white mass. Eventually, the white lint-like material disappears,
leaving the bleached, grayish-brown, decayed wood in either a stringy
or a somewhat amorphous condition.
Figure 200. Red rot decay affects the heartwood and is typically associated with old growth ponderosa pine.
Both stages of red rot are usually visible in a board sawed from a decayed
log. At the point where rot started in the trunk heartwood, advanced
decay often forms a cavity. Extending in both directions from this
point are more or less continuous columns of advanced decay, bordered
by incipient decay.
Biology: The spores are dispersed by wind,
land in cracked bark crevices of dead branches, and germinate to
colonize the area between the bark and wood and eventually the dead
wood, provided it has intact bark. The red rot fungus fruits abundantly
on the lower side of decaying dead material in close contact with
the ground. The flat, white fruiting bodies appear about 4 years
after infection and then develop annually during the rainy season
for about 6 years.
Effects:Dichomitus squalens is
the most common decay of ponderosa pine in the Southwest. It is
a decayer of slash (a saprophyte) as well as a heartrot in live
trees. It has been reported to cause a significant amount of cull
in live trees 150+-years-old when grown for timber. As with other
decay fungi, D. squalens provides habitat for cavity nesting
birds and other wildlife. Although this fungus is of minor occurrence
on living trees in second growth forests, there are reports of extensive
decay of young trees (<80 years) in localized areas.
Similar Insects and Diseases: Many fungi
decay ponderosa pine slash, but D. squalens is probably
the most common.