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Black Knot Fungal Disease is the common name for the fungal tree organism Apiosporina morbosa, which causes a devastating tree disease in many places in Canada, including Alberta. It is often found on commercial and private trees, as well as trees in the native, natural environment. In Edmonton, several species of Cherry, and Plum trees are affected. Most commonly, Mayday trees, Chokecherry Trees and Pin Cherry Trees.
Initially, a small swelling or green, olive-coloured gall will develop along branches of the tree. These green swellings can grow up to 2-3 years before maturing into unsightly black growths. Once infected, the fungus grows internally, and will “girdle or choke -off” the tissue, causing the branch to decline , and potentially over time, resulting in branch death of complete tree loss.
The most obvious way to recognize Black Knot Fungal Disease are the visible black growths also known as “Knots”. These black “growths”, are usually spotted by an untrained eye, when the tree has lost all of it’s leaves. These growths release fungal spores into the air. Spores spread more rapidly and further with the aid of wind, rain splash and insects or birds landing from branch to branch.
There are several ways to help control and/or slow the spread of Black Knot Fungal Disease. The most direct way, when possible, is to prune for removal of the swellings well below this area during late Fall or Winter. This will allow the knots to be clearly visible, as there will be no leaves on the tree. As well, at this time the fungus will be less likely to spread, as the trees are dormant. Secondly, cleaning or disinfecting of the pruning tools, followed by correct disposal of the removed, diseased branches, are crucial in control. “Correct Disposal” consists of burning, burying or removal of infected tissue from location. Note that even after pruning, these fungal spores can continue to disperse for several months.
A Certified Arborist is able to identify, and correctly put into place, a plan of action for your tree’s monitoring, health and maintenance. Edmonton’s Best Arborist can aid you in keeping your trees disease- free and beautiful!