Armillaria root disease

Armillaria Ostoyae

Armillaria root disease is the most important disease affecting timber production in southern B.C. It is a native pathogen that affects all native B.C. trees species and plays an important role as a source of biodiversity in unmanaged forests.

One this page:

• Description
• Host tree species
• Damage symptoms
• Management
• Identification images

Description

Armillaria ostoyae is one of five species of Armillaria found in BC. It spreads by root to root contacts and through soil by means of rhizomorphs. It can persist for years after harvest in infected stumps and roots.

Extensive growth reduction and mortality among infected trees occurs in interior forests. The time from initial infection to mortality increases as trees age. In coastal Douglas-fir managed stands, mortality typically occurs in trees between 10 to 20 years of age while in the interior mortality continues throughout the life of the stand.

Armillaria root disease is found in southern regions of British Columbia. View the distribution map.

Host tree species

All native conifer species are susceptible to Armillaria root disease. Some species are more susceptible than others with Douglas-fir, subalpine fir, and spruce being highly susceptible and hardwoods, western red cedar, and mature larch being less susceptible.

Damage symptoms

Symptoms of Armillaria root disease (and all other native root disease) include reduced height and diameter growth, yellowing and thinning of foliage, stress cones, and death. In addition, Armillaria infected trees may have basal resinosis (pitching at the base of the tree).

Mycelial fans under the bark are the most reliable way of identifying the disease. When spread occurs on dead trees these appear as sheets rather than fans. These sheets of mycelium also occur with Armillaria sinapina, another species of Armillaria that is commonly found on dead conifers and produces similar looking mushrooms. Other signs include rhizomorphs and clumps of honey mushrooms at the base of the tree. Honey mushrooms are most commonly produced in the fall prior to the first frost.

Read a detailed summary of Amillaria root rot symptoms (PDF, 205KB)

In severely infected stands Armillaria can produce large discrete infections centers that may be visible from the air. In stands with lower incidence, mortality may be scattered throughout the stand, especially on stressed or suppressed trees.

Management

There are several interventions to address Armillaria root disease to minimize future losses. Regenerating with less susceptible species that are ecologically appropriate or the removal of stumps post-harvest when appropriate are the recommended treatments for Armillaria root disease. Read a detailed guide on root disease management. https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/forestry/forest-health/forest-health-docs/root-disease-docs/rootdiseaseguidebookjune2018_4.pdf

Identification images

Further reading

For more information about amillaria root disease, read the field guide and view additional images in the Field Guide to Forest Damage in B.C. (PDF,6.5MB)