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  • Writer's pictureNeighbours Tree Company


Updated: Feb 16

Black knot is a common disease that certain species of trees in Alberta are susceptible to.

Read below for more information!

Black Knot affects multiple tree species in Alberta

What is Black Knot?

Black knot is a serious and progressive fungal disease that initially infects twigs and branches. As the disease progresses these swellings form hard, rough coal-black knots (also known as abnormal black clumpy growths) that girdle and kill the affected parts. If not taken care of, it can become severe and eventually stunt and kill the tree. Its crucial that if you notice your tree might have black knot, to contact your local arborist immediately in order to prevent any further damage and have it removed as soon as possible.

What Trees are Mainly Affected by Black Knot?

Black Knot mainly affects Prunus trees including ornamental, edible, and native plum and cherry trees in Alberta. See some common tree types that are commonly affected below:

  • Flowering Almond

  • Mayday

  • Wild Plum

  • Apricot

  • Flowering Plum

  • Mongolian Cherry

  • Japanese Plum

  • Nanking Cherry

  • Korean Cherry

  • Choke Cherry

  • Sour Cherry

  • Pin Cherry

  • Prunus hybrids

How to Control Black Knot?

To control black knot we recommend pruning the infected parts during the winter while the tree is dormant and they are super easy to see (try to avoid pruning in the spring when the fungus is still active). The large knots on the limbs are cut away and removed, allowing the wound to be treated. It is important to keep an eye out & prioritize tree with black knot sooner than later to prevent any long term affects that may be unmanageable down the road.

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