What is it?
Black Knot Fungus is a very common disease in Prunus family (common cherry trees, mayday tree, schubert choke cherry tree, plum trees in calgary). It is a fugus called Apiosporina morbosa. It will affect the look and the health of your tree.
Symptoms
- A small, olive-green gall will start to develop on affected branches.
- A mature, black, hard gall will then develop over the summer.
Damages
- The black knot will slowly swallow and choke the branch to death.
- Mature galls will produce and release a vast amount of spores during the bloom period, resulting in a rapid increase in infections.
- Heavy infestation will severely affect the health and aesthetic of the tree.
What to do?
- Remove all visible black knot branches during early spring, late fall or winter when trees are dormant and knots are easy to see.
- Avoid pruning in spring time when the fungus is active.
- Remove diseased branches back to appropriate branch collar.
- Sterilize pruning tools with 25% bleach, 75% water solution to prevent further spreading.
- Destroy diseased wood immediately, dispose to black bin instead of green bin.
- Regular monitoring and keep the tree healthy and free from stress.
- Chemical control is not effective.
- Avoid planting the same or similar types of trees.
Other resources:
https://www.calgary.ca/parks/pests/black-knot-fungus.html
https://tidcf.nrcan.gc.ca/en/diseases-caused-by-pathogens/factsheet/4