Black Knot

black knot

Black knot is a fungal disease that has become an increasing problem in Alberta. Affecting primarily Mayday and Schubert Chokecherry trees, it can spread to Plum, Apricot and Cherry trees. Once spotted, Black knot should be removed to help control the fungus from spreading within the canopy and to healthy trees around.

What does Black knot look like?

At first, it may be very difficult to spot Black knot. Greenish brown areas will swell and are hard to spot with the un-trained eye. Eventually, the areas darken and harden to form a black, tar like deformation. It is easier to spot when the tree is in it’s dormant state, as the leaves are off the tree. Black knot can be obvious, present in many affected branches of the tree, or present as a single affected swelling.

How does it spread?

Like all fungus, Black knot spores thrive with periods of warm, humid weather. Wind, insects and wildlife can also help with transport. Black knot will spread within the canopy of the tree as well as to other trees around. Black knot will even spread into the main stem of a tree.

I think my tree has Black knot. What should I do?

Consider hiring a professional to properly prune your tree. It is usually best to remove Black knot when the disease is in its dormant state, leaves are off the tree, and it’s much easier to see. If you do plan on removing Black knot yourself, plan to sterilize your equipment during use, and prune back to at least 6-8 inches from the visible knot. Sadly, sometimes trees are so badly ridden with Black knot they have to be removed. An ISA trained Arborist will be able to give you guidance on whether the fungus is maintainable or if the tree needs to go.

Why Tree Topping Hurts

tree silhouette

Tree topping may seem like a good idea to control the height of your trees. Some trees are planted in areas with no room to grow or have become much larger than expected. No properly trained Arborist will tree top, and no Arborist will recommend it. Tree topping can be detrimental to the health and aesthetic of the tree, and harder on your wallet!


There’s a few key point of why tree topping is not a common, proper practice.

Tree topping will send the tree into shock.

  • Foliage from the canopy of the tree shields the suns hot rays and provides shade. When a large amount of foliage and canopy growth is removed, scalding may occur.

Tree topping causes rapid, weak new growth.

  • Removing so much of the tree at once causes the tree to stress. Rapid water sprout growth will occur, which overtime, is far weaker than the original tree canopy and has higher potential to fail.

Tree topping is unappealing.

  • A healthy, properly pruned tree will add value to your landscape for years to come. A topped tree is unattractive and can do just the opposite.

Tree topping adds up!

  • Sure, it is usually cheaper….in the beginning. Proper pruning may cost more at first, but it will save in the long run. A topped tree may not recover and die – adding additional removal costs and weak branches may fail, causing more expenses.

What can you do?

Prevention is key! Do research or talk to a professional before planting and choosing your tree. Get an idea of mature height and canopy spread. Plant the tree in an area where is has room to grow and thrive. Trees need space to live and your landscape will appreciate it in the long run!

Integrated Pest Management


If you seem to be overrun by a plague of insect pests on your trees or shrubbery, you might want to consider Integrated Pest Management. In the long term, this strategy aims to rid your property of insects that can seriously harm – or even kill – your plants.

The Lakeland College Pesticide Applicator Course, 2016 edition states that IPM is systematic decision-making process that aims to prevent pests from becoming problems, and to determine what actions to take if pest problems occur.

There are 6 key elements to IPM.


Choose landscape plants that are less insect and disease prone that others. Create growing conditions that aid with healthy growth. For example-add organic matter through soil and/or nutrients to the ground.


If you observe an insect problem, try to find out which pest is causing the damage through research or speaking with a professional. It is important to find the correct source of the damage. If an insect is improperly identified, control measures may not work.


This includes checking for damage and presence of the insect. Monitoring is key to find the life stage of the pest. For example-some control measures will work better while the pest is in its larvae stage, while others will work best when the insect is abundantly active at the leaf’s surface. Beneficial insects may also be present and enough of them may be active to keep the pest population in check.


In IPM, threshold levels are placed into 2 categories. The injury threshold is when the pest is causing unacceptable damage and is detrimental to the plant. The action threshold is when treatment should begin to prevent injury from occurring.


There are 5 different aspects of treatment in IPM.

  • Cultural
  • Mechanical/Physical
  • Biological
  • Behavioural
  • Chemical

We will just touch on 2 of these.


In the event of an aphid infestation, pruning would be considered a way to reduce pest population. Thinning a canopy of water sprouts, deadwood and crossing/rubbing branches would increase airflow circulation throughout the tree. This would become a less favourable environment for the pest.


In a bad infestation of Yellow Headed Sawfly, chemical control may be used when other control measures will not work. As Sawfly is an extremely damaging insect (especially to young plantings), and highly damaging when it large numbers, it is best to control them at first sight. Control measures that do not include chemicals would include picking off the insect and destroying them, or spraying them off the tree with high pressure water. When this does not work, insecticidal soap or Trounce should control their population.

As always, discuss your options with a professional!