Signs of Black Knot Disease and What to Do: Calgary Landscaping by Mirage

Signs of Black Knot Disease and What to Do: Calgary Landscaping by Mirage

Signs of Black Knot Disease and What to Do: Calgary Landscaping by Mirage

Mirage Landscaping of Calgary provides premier residential and commercial full-service landscaping design and maintenance. 

We love our trees and work hard to protect them.  Black Knot disease has always been common in Calgary, but in the last few years has become more and more prevalent.  The fungus itself has been present in Alberta for decades now and is endemic to our environment. That is to say that dormant spores lay everywhere and vigilance is the only precaution to take.

For the first several years of its reproductive cycle, Black Knot appears green and like nothing unusual. However, as it grows the fungus not only saps the tree’s vigour, it weakens the affliction site, making the tree more susceptible to insect invasion and prone to sustaining winter injuries too.

Our damp springs of recent years have resulted in prime growth conditions for the spread of Black Knot. Just as toadstools appear after spring rains, the fungus thrives in times of abundant moisture. The fungal site swells as spores build within it, eventually bursting and tossing tens of millions of spores into the air. These spores then land upon downwind hosts and begin their reproduction cycle again.

If you have any of the following trees on your property, and particularly if they are younger trees in hardest hit southwest of Calgary, they may be at risk for black knot infestation if they are not already being subjected to it:

  • Amur Cherry
  • Mayday Tree
  • Apricot
  • Mongolian Cherry
  • Black Cherry
  • Nanking Cherry
  • Chokecherry
  • Pin Cherry
  • Dropmore Cherry
  • Cultivated Plum
  • Flowering Almond
  • Wild Plum
  • Flowering Plum
  • Prunus Hybrids
  • Japanese Plum
  • Sand Cherry
  • Korean Cherry
  • Sour Cherry

As you can see, the trees which are susceptible are actual or ornamental fruit trees for the most part. 

What Black Knot Does and What To Do About It

Foliage can often obscure all but the largest Black Knot growths from easy view. However, if left unchecked, black knot fungus will eventually kill its host tree.

The black knots which eventually develop appear mostly upon the small twigs and branches, but may also afflict main scaffold limbs and even the trunk. Knots most often form where leaves emerge from the branches. Fully developed knots can ultimately encircle the infected branch and grow to be in excess of a foot in length.

There is no real cure for Black Knot tree fungus. Controlling its spread is the only price effective option for most people to consider. Fortunately, if you spot Black Knot fungus in time, most of its spots upon most trees so afflicted can be “treated” via judicious pruning. 

Though summer is not ever recommended pruning season, Black Knot is a serious enough problem to ignore that rule of thumb. Be sure to prune at least 2-4 inches, (5-10cm), below the site of the knot to ensure its complete removal. Be careful not to rupture a mature knot and accidentally release its spores. The best methods of disposing of mature black knot is to either burn of bury the removed branch segment.

If the fungus is afflicting a scaffold branch or the trunk itself, you are going to need to consult with a certified arborist of even a tree surgeon, as careful removal of the site in question is the only long term strategy for saving the tree, if it is not already too lateOver 50 trees have been claimed by black knot in southwest Calgary alone this year.

Please take a moment and thoroughly check any deciduous trees growing on your property. If you see any sign of Black Knot, especially if it looks hazardous for you to reach and get rid of, contact us for a free quote on removing it.


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