Hypoxylon canker of aspen (Hypoxylon mammatum)

Last Review/Updated: January 6, 2003

Hypoxylon canker of aspen (Hypoxylon mammatum (Wahl.) J.H. Miller) is one of the most common diseases on aspen in North America. However, this disease is considered to be less serious in western North America including Alberta than in eastern North America. This disease generally affects trees that are under stress.

Primary Hosts and Distribution

  • Trembling aspen (Populus tremuloides Michx.)

This disease is found throughout Alberta.

Disease Cycle

Airborne spores produced on cankers penetrate through wounds of the bark. In the first year of infection, yellowish-orange discoloration of the bark can be seen often surrounding a branch stub or dead branches. During the second year of infection, the first spore stage (asexual) is characterized by gray-black pillar structures that push up and rupture the bark. Continuing after two years, sexual fruiting structures (perithecia) replace the asexual fruiting structures. Spores (ascospores) produced in perithecia are airborne and cause infection likely through wounds on stems.

Detection and Damage

Look for the following signs and symptoms:

  • Yellow-orange sunken cankers (depression);
  • Split bark with brownish sap forming around the margins;
  • Gray pillar-like structures under the bark;
  • Additionally, white fans of fungal tissue around the infected area under the bark.

Trees structurally weaken behind cankers in the lower stem and become susceptible to breakage. Hypoxylon canker can eventually girdle and kill a tree in 3 to 4 years.

Management

Some management techniques include:

  • Avoiding damage to trees (e.g. while harvesting; ranching; or using equipment);
  • Surveying and periodically monitoring stands;
  • Harvesting an infected stand should more than 25 percent of the aspen be infected;
  • Removing severely cankered trees where breakage could be hazardous;
  • Maintaining fully stocked stands and a closed canopy.