Black Knot Disease Maintenance

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Residents are responsible for trimming and maintenance of infected trees located on their own property.  The Town of Three Hills has a maintenance program in place for trimming and maintenance of trees located on public property.

Black knot is a tree and shrub disease that affects members of the Prunus family-like chokecherry and pin cherry and is a common problem for residents of Three Hills. You may have seen it in your yard or neighbourhood.

You can easily identify the disease. It develops on twigs and branches and looks like lumps of thick, black, tar-like swelling that may vary in size from 1/2 inch to more than 12 inches in length.

Black knot has been reported on 24 species of Prunusin North America but is most commonly found on wild and cultivated plum and cherry trees.

The Problem with Black Knot Disease:

Black knot disease damages and kills trees by affecting their branches. The spores of this fungus are spread by wind and rain to the young twigs in the spring. Black Knot will dwarf and misshapen trees, making them stressed and unhealthy, and can infect other healthy trees in your yard, your neighbour’s yard, and throughout your neighbourhood.

If not controlled, the disease destroys garden aesthetics, disfigures branches, and eventually kills trees. Young, infected twigs may die during the first year of infection. Larger branches may take several years to show signs of damage. The infected trees decline and become more symptomatic with each growing season. The infection stresses the entire tree, causing it to weaken, decline and eventually die.

How to eliminate Black Knot Disease:

Fortunately, this fungus is easy to remove by cutting off diseased branches and disposing of them immediately. Do not compost or leave them in your yard. Diseased branches and trees can be taken to the landfill, however, notify the attendant as to ensure they are appropriately separated.

It’s easier to identify infected branches and twigs in the winter. It’s also the best time to remove any suspicious branches and twigs as the spores will not spread as readily, protecting your trees and other trees in the area.

Pruning Tips and Techniques:

  • All shoots and branches bearing knots should be pruned during the winter. This pruning should be completed before the time that the buds first break in the spring.
  • When pruning, cuts should be made at least 15-20 cm (6-8 in.) below the knot.
  • Use sharp pruning tools like clippers, shears or saws to make clean cuts.
  • Sterilize your tools between cuts by soaking them in a 1:3 bleach and water solution, or by using a dish soap solution.
  • Dispose of diseased branches by putting them in the trash, burying or burning them. Do not put them in the compost in your yard or in the general landfill compost area as they can spread spores for months after removal.

Replacing Your Trees:

Sometimes the disease will have progressed enough that the tree cannot be saved and removal is necessary. You can always plant another tree once the diseased tree has been properly removed. When selecting trees for new planting, consider varieties that will do well in our climate, like the Amur chokecherry (Prunus maackii).

Find Tree Maintenance Companies in Three Hills on the Towns  Business Directory listed under Contractors, Landscape & Maintenance.