Black Knot
Black knot fungus (Apiosporina morbosa) is a common disease of the Prunus family (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 family 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.
Pruning and Disposal
To control black knot on infected trees, the City of St. Albert prunes trees for this disease every winter when the fungus is dormant and recommends residents do the same. The infected areas should be pruned out, and cuts made at an optimum 15 to 20 centimetres back from the infected area. To ensure pruning equipment is properly sterilized after removal, all equipment should be washed down with a mixture of water and bleach (10 per cent). The multi-purpose cleaner, Spray Nine, is also effective.
To help keep St. Albert a Tree City, please bring any diseased branches to the Compost Depot and place in the Diseased Branches pile, or the Mike Mitchell Recycling Depot during the winter months while the Compost Depot undergoes its seasonal closure.
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: May 23, 2024