Black Knot

Black Knot fungus (Apiosporina morbosa) is a common disease of the Prunus species (i.e. Schubert, Mayday and Plum trees). The fungus forms swollen black cankers or "knots" on the stems and twigs of infected trees. The disease can be spread to other trees of the Prunus species by rain, insects, birds and unsterilized pruning equipment. Because it is known to spread rapidly, it has the potential to seriously deform the trees and spread to other trees in the area.

To control black knot on infected trees, the City of St. Albert prunes trees for this disease every winter when the fungus is dormant. The infected areas are pruned out, and cuts are made at an optimum 12 inches below the infected area. To ensure pruning equipment is properly sterilized after removal, all equipment is washed down with a mixture of water and bleach (10%). The multi-purpose cleaner, Spray Nine, is also effective. Residents are asked if they are removing infected branches from their trees to bring them to the Compost Depot and place them in the diseased wood pile for proper disposal.

For more information on how to manage black knot disease, please visit Alberta Agriculture and Forestry. 

Reporting Damaged, Broken or Diseased Trees

If you would like to report a tree that needs to be trimmed or if it is damaged, broken, or diseased, please report the issue online or contact Public Operations (formerly Public Works) at 780-459-1557. These requests are recorded and sent to the appropriate section. They will then be inspected and scheduled for repair based on their level of severity.

Related Pages

Last edited: November 25, 2021