About this Tree Concern
In Ontario, it is very common for cherry, plum and other fruit trees to get black knot. This can cause significant damage to the tree if not managed properly.
The disease is characterized by greenish-brown to black swellings on the stems of trees. These swellings, or knots, can become quite large, sometimes encircling the entire limb of the tree. The spores of the fungus are released following periods of warm, wet weather and can be spread by rain, wind, birds, and insects.
Remediation
If you see black knot, infected branches should be pruned out during the winter, at least 15-20 cm below the knot, to prevent the spread of the disease to other limbs and trees.
All pruned material should be destroyed by burning or removing it from the site, as the knots can produce spores even after removal. As a last resort, fungicides can help manage black knot, but they are not a substitute for proper pruning and sanitation practices.
If you have trees affected by black knot, it’s crucial to take action to manage the disease and prevent its spread to other trees in the area.