-- Root rot organisms, A. tabescens and A. mellea, cause
major losses throughout the United States. Windthrow of infected trees
in urban and high-use areas contribute to the importance of root diseases.
Additional losses occur from loss of vigor.
Fungi (figure 59). -- In the fall, clumps of yellow mushrooms grow
on the ground near the tree and occasionally on the bole several feet
above the ground. Thin black strands of mycelia (rhizomorphs) are produced
on the root surface which resemble black shoe laces. The mushroom has
decurrent gills and produces white spores.
the Injury. -- Infected trees may have low vigor. Roots may show
various degrees of decay and have rhizomorphs on the surface. Frequently,
root rot is evident only on wind-thrown trees. The rate of spread in
the soil is about 1 foot (0.35 m) per year.
-- The fungus can live in dead roots and stumps for many years. Rhizomorphs
spread through the soil from infected roots to nearby healthy roots
which they then infect. Mushrooms produce abundant spores, but they
are not important in infection of living trees. The fungus is most successful
on slow-growing trees.
-- Spread can be controlled by removing the infected tree. Sterilize
the soil before replanting. Any cultural practices that reduce stress
and increase tree vigor will prolong tree life.