Check Your Trees for Black Knot Disease
A proliferation outbreak of Black Knot Disease on trees has been observed in Olds. This dreaded fungal disease affects Apricots, Plums and Cherries in the Prunus genus. This is most prevalent in Schubert Chokecherry and Mayday trees here in Alberta although other cherry trees and plums can certainly be affected.
How to Identify Black Knot?
It starts as olive green gall or swelling and over two to three years will grow into a bulky, black, tar like growth on the affected branch. If it is not dealt with it will spread to other parts of the tree internally and externally. When the gall is mature it releases huge amounts of spores in the spring that are airborne infecting other trees in your neighbourhood. Eventually the branch above the infection will die back. The tree will not die immediately but suffer a long slow death when not controlled and if the infection becomes extreme.
How to Control Black Knot?
It is best to prune in late autumn after the leaves have fallen and right through the winter into early spring before you see any new buds starting to swell. It must be cut out of the tree at least 12 inches below the infected area. Make a proper pruning cut, do not leave a stub. Make sure that the infected branch is disposed of properly, best to burn immediately, do not put it into the compost bin.
Please ensure all pruning equipment is sterilized following each cut, as the disease transfers easily.
If you must remove your tree, do not plant another Prunus species in the same spot. Make sure your trees are healthy so they are less likely to be infected by the spores floating through the air in spring. Consider hiring a certified arborist if you are not sure your tree is infected or not sure what to do.