Many trees in Calgary are infected by Black Knot Fungus or by Black Knot Disease, the most commonly used names for this infestation. Black Knot Fungus is easily diagnosed by a branch thickening, a texture change, and a darkening of the affected branches. This fungus spreads easily from neighboring trees through wind and rain.Black Knot is most commonly seen in Chokecherry, Schubert Chokecherry, and Mayday Trees
Which of my trees should be inspected for Black Knot Fungus?
More or less all of the Prunus Family can be affected by Black Knot – some are more prone to the disease than other varieties.
Is my tree infected with Black Knot Fungus?
These trees certainly are heavily infected
Can Black Knot Fungus be treated?
This infestation can not be cured. The only mitigation option is pruning (prune back at least one foot from the knot). Black Knot hastens the death of the tree but many trees can live for years with a small infection.
If you have a tree in a early stage of Black Knot infestation we would advise pruning the tree – but do your homework, if pruned incorrectly, you could damage the tree and make it more prone to disease. Another option is to call your Aborist for a professional pruning. If the tree is heavily infected like the picture above it is advised have the tree removed and have the infected branches properly disposed of. Since this disease spreads quite easily it is the neighborly thing to do.