Tree Squad can help trees with Armillaria Root Rot

Armillaria Root Rot

Many tree species

What you will see:

  • White fungal mats can usually be found under the bark
  • Black shoestring structures
  • Rhizomorphs (mass of mycelia)


Life cycle:

  • Mushrooms present in late August through October
  • Spores are distributed by the wind to exposed wood or injured bark
  • Spores germinate and produce mycelia that infect the bark and sapwood killing the cambium
  • Fungus can persist from several months to many years
  • Honey-colored mushrooms may appear at the base of the plant (Honey fungus)
  • Mushrooms are edible
  • Foliage thins and discolors, turning yellow, then brown
  • Branches may die-back, shoot and foliar growth are reduced

Cultural practices:

  • No labeled fungicides are effective against Armillaria
  • Preventative
  • Reduce moisture problems
  • Reduce soil compaction
  • Don’t damage bark tissue or roots
  • Root Enhancement System (RES)
  • Increases population of competitive soil organisms
  • Increases growth rate of callus tissue
  • Increases root growth and tissue resistance
  • Increases soil porosity, decreases soil moisture


Cultural practices:


  • Remove soil from the base to a depth of 9-12 inches
  • Leave the trunk exposed to air
  • Keep the upper roots and crown area as dry as possible
  • Dry conditions will kill the fungus

Additional Armillaria Root Rot Information:

Armillaria root rot is in virtually all tropical and temperate regions in the world. You will find it in the continental United States in nearly every state. Host tree species are in the hundreds, shrubs, vines, and forms in forests are victims of this disease.

Armillaria root rot fungi live as parasites on the host's tissue or as saprophytes on dead woody material. The fungi that causes this disease is mellea Kummer. Research indicates there are several different types of fungi that are related and often involved in this disease. A generic term Armillaria is often used to represent the entire group of fungi.

All of these fungi are natural components of any forest. In most cases they live on the coarse roots and lower stems of conifers and broad-leaved trees.
In its parasite form, this disease causes mortality, growth reduction, and wood decay. It can kill trees that are already weak from pests, climate, or competition. This happens throughout the United States, but is particularly common in the forests of the East. This fungi infects healthy trees. It makes them susceptible to other attacks from insects.

The disease has multiple names. Shoestring root rot refers to the rootlike fungal structures, known as rhizomorphs, that spread it. Honey mushroom, mushroom root rot, toadstool disease, and honey agaric, are different names for the same disease. Conifers are another target. They respond to infection by creating a copious flow of resin, which is the reason for the name resin gut or resin flow. When the infection afflicts oak trees, it is called oak fungus.

Symptoms of trees infected with Armillaria are limited and difficult to detect. The mushrooms produced at the base of the tree are more obvious and tend to crown near the lower stem.