Black Knot Treatment & Prevention


Black Knot Treatment & Prevention
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Black Knot Treatment & Prevention

You may have noticed black clumpy growths on the trees in your yard and around Sturgeon County. It looks like masses of burnt rope wrapped around the branches and it affects a wide range of trees, including plum, cherry, chokecherry, and mayday trees.

This is called Black Knot Disease.

Black Knot is a very common fungal disease and spread when spores are released following periods of warm, wet weather and can be spread by heavy rainfalls, wind, birds and insects. As the infection spreads throughout the tree, it can cause disfigurement and reduce the growth of the branches. If it becomes heavily infected, the tree can become stunted and may eventually die from the disease.

How To Control Black Knot
Prune out all knot-bearing branches during late fall, winter or very early spring when plants are dormant, and when the knots are easy to see. Diseased branches can release spores for up to four months after being cut off the tree, so it’s important to destroy the diseased wood immediately (burn or bury it). Also ensure you clean your pruners with bleach or hydrogen peroxide to prevent further spread of the fungus.


  • When planting new trees, consider selecting varieties with known resistance to the disease.
  • Avoid planting new trees near areas with known problems.
  • Consider hiring a trained professional for pruning activities.

For more information, please contact Agriculture Services at 780-939-8349. You can also read more on our Black Knot Disease brochure.

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