Black Knot

Black Knot is a fungal disease caused by Apiosporina morbosa, it can affect a variety of different trees. It appears as rough, black, tar-like swellings on branches and twigs. If left untreated, it can eventually kill the tree and spread to others nearby.

This fungus is highly contagious and spreads through wind and rain. Early removal and proper disposal are essential to protect surrounding trees.

Important: Black Knot will continue to infect other trees in the area if not addressed.

For a list of affected plants, visit the Government of Alberta’s Black Knot page.

 You should remove Black Knot during the tree’s dormant season—late fall through early spring—when the fungus is inactive and easier to identify without foliage in the way. Pruning during this time also reduces the risk of spreading spores to healthy parts of the tree or nearby trees. 

Timing
– Prune during the dormant season—late fall to early spring—when the fungus is not actively spreading and the knots are easier to see.

Pruning

– Cut 6 to 8 inches below each knot to ensure all infected wood is removed.

– If the knot is on the trunk or a major branch and cannot be removed entirely, consult a professional—partial pruning can make it worse if done incorrectly.

Tool Sanitation
– Disinfect pruning tools between every cut using a bleach solution (1 part bleach to 9 parts water) or rubbing alcohol to prevent spreading the fungus.

Disposal
– Never compost infected wood.
– Burn it or dispose of it in sealed bags through municipal yard waste programs.

Ongoing Monitoring
– Check the tree annually and remove any new growths promptly.

Removing Black Knot might seem simple, but it's much easier—and more effective—for us to handle it professionally.

– We know what to look for: Some growths are hard to spot, especially early infections. We’re trained to identify all affected areas, not just the obvious ones.
– Proper cuts: We cut well below the infected areas (6–8 inches) to stop the fungus from returning—most homeowners cut too close and the knot grows back.
– Tool disinfection: Every cut needs sanitized tools to avoid spreading the fungus. We follow strict protocols that are easy to miss during DIY jobs.
– Safe disposal: Black Knot must be properly destroyed (not composted). We handle cleanup and disposal, so you don’t risk re-infecting nearby trees.
– We work faster and safer: With ladders, saws, and proper pruning gear, we can access hard-to-reach branches safely and efficiently.

Let us take care of it properly—so it doesn’t come back or spread to your neighbors' trees.