Diagnosis - Bashwood or Linden Problems on Trunk and Branches
Unusual Woody Growth on Trunk

Ganoderma Root

Ganoderma root and butt rot or Ganoderma spp.

  • Leaves are smaller in size and turn yellow earlier than normal
  • Canopy appears thin with few leaves and multiple dead branches
  • Fungal conks, a semicircle shelf fungi, can be found from the base of the tree up to 3 feet high on the trunk
  • Conks are reddish brown and shiny on top, white and porous underneath, a rim of white may be visible on the edge of growing conks
  • Infected wood at the base of the tree is white, soft, stringy or spongy
  • Infected trees frequently break or fall over in storms
Photo by M. Grabowski, University Of Minnesota
Photo by M. Grabowski, University Of Minnesota
Photo by M. Grabowski, University Of Minnesota

Varnish fungus rot, caused by the fungus Ganoderma lucidum and (unvarnished) fungus rot, caused by G. applanatum infect the roots and lower trunk (butt) of many deciduous trees and some conifers. They attack the lower heartwood, and at advanced stages damage the structural integrity of the host tree, often resulting in windthrow (the potential to be uprooted or broken by wind). Maples, oaks and honeylocusts are particularly susceptible, although ashes, elms and many other deciduous trees and some conifers can be attacked.

Trees affected by fungus rot may exhibit yellowing, wilting, or undersized leaves and dead branches. Tree vigor may decline as decay of the sapwood advances. The first visible sign of infection is often the formation of fruiting bodies (single or in clusters) on the lower trunk and exposed root areas. The fruiting bodies are conks:  shelf-like in appearance and up to 14 inches wide. The upper surface of varnished fungus rot is typically red-brown with a white edge, shiny, and with a lacquered appearance. Conks of the unvarnished fungus rot are brown with a white edge weathering to grey. Both have a white, porous surface (when fresh) on the underside. Young trees as well as older, larger ones can be killed by this disease. Unfortunately, by the time the conks are noticed, it is too late to reverse the infection. The rate of decay can lead to death in as little as 3 to 5 years from the time of infection, and appears to be determined by tree vigor, which is often influenced by environmental stresses.

New spores released from the conks are dispersed throughout the summer during humid periods, and infect open wounds on root flares and lower trunk areas of susceptible trees. The spores germinate, and the infection advances to attack the sapwood of major roots and the lower tree trunk. The amount of decayed wood increases year after year, resulting in dangerously soft, spongy wood in the part of the tree that serves as its anchor. The conks are annual; new conks may be produced each summer and fall, after which they die and deteriorate.

Information source: Missouri Botanical Garden

Heart Rot

Heart rot or Trametes versicolor, Climacodon septentrionalis,
Polyporus squamosus and others

  • Fungal fruiting bodies arise along the stem; often near a pruning wound, crack or other wound
  • Many colors, shapes and sizes of fungal fruiting bodies may be seen
  • The canopy may show no symptoms or may have small yellowing leaves or dead branches depending on the extent of the trunk decay
  • In cross section of the trunk, the wood at the center is discolored, soft, crumbling, stringy or spongy
Photo by R. L. Anderson, USDA Forest Service, Bugwood.org
Photo by H.J. Larsen, Bugwood.org
Photo by A. Kunca, National Forest Centre - Slovakia, Bugwood.org

Heart disease in trees is caused by fungi invasions. Although there are many species of fungi that cause decay in living trees, most important are those fungi that cause heart decay often called heart rot. These pathogens usually enter the tree as a result of injury Such points of entry may come from broken branches caused by wind, fire, lightning, and even from improper pruning by us humans. Once inside the tree, fungi cause decay. Interestingly, heart rot fungi do not invade the living wood of healthy trees.

Detecting heart rot can be difficult. Since this type of decay takes place internally, it can remain out of sight for many years. Usually, in the latter
stages of heart rot, mushrooms grow on the trunk or branch. This is one of the first visible signs that a fungal pathogen resides within the tree. Unfortunately, as decay progresses, the heartwood is destroyed; and the integrity of the tree’s strength becomes a serious issue.

These external mushrooms are the fruiting bodies of the fungi. They are generally called conks or bracket fungi. These visible conks produces spores. Spores become wind-borne, microscopic, seed-like structures. The wind carries spores to other susceptible trees thus perpetuating the life cycle of conks. These fungi appear bracket-like, attached to the tree and varying greatly in size, color and texture. Note: The visible presence of conks
calls for investigation.

Eliminating or minimizing heart rot is accomplished by keeping one’s tree healthy. When pruning branches, make cuts just outside the branch collar so proper mending can take place. Shape trees at an early age, so major branch removal creates small wounds.
Remove broken branch stubs immediately following storm damage. Have suspected heart rot trees checked by an arborist to determine if sufficient live wood is present for structural safety. Check trees every few years to be certain new growth is maintaining sound structure.

I am certainly not a doomsday advocate, but I do know that large tree trunks and main branches revealing numerous conks are certain indications that little sound wood remains to support the tree.

After all, one doesn’t want heart disease, more commonly called heart rot, in trees to cause the homeowner heartache when his or her tree comes tumbling down damaging, or possibly destroying, his or her home.

Information source: University of Nebraska

Sapwood Rot

Sapwood rot or Schizophyllum commune and Cerrena unicolor

  • Dead branches within the canopy
  • Groups or rows of small (<2 inches wide) semi-circle self fungi along killed branches or on the main trunk
  • Schizophyllum shelf fungi are white and appear fuzzy on top
  • Cerrena shelf fungi are white to greenish grey and have concentric rings on the surface
  • Common on trees with an open wound or crack
  • Wood below fungal shelves is yellowish to white, crumbly and decayed; bark around fungal shelves is killed and often falls off

Information source: University of Minnesota Extension

Photo by A. Kunca, National Forest Centre - Slovakia, Bugwood.org
Photo by A. Kunca, National Forest Centre - Slovakia, Bugwood.org
Photo by M. Grabowski, University Of Minnesota
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