Tree diseases are common and effect any part of the tree. Tree diseases causing organisms are difficult to identify and are not visible to the human eye. Only an experienced and expert ISA certified arborist can easily identify tree diseases. A correct diagnosis is a first and most important step in developing and applying a correct treatment. 

Black Knot

Black knot is a very common tree disease, which is caused by the fungus Apiosporina morbosa. It affects chokecherry trees (Schubert chokecherry and Mayday), apricot trees and other trees in the genus Prunus. Besides having a negative impact on the tree’s appearance, these tree diseases can also lead to the eventual death of the tree.

A common way to identify black knot is to see whether your tree has black, tar-like swelling points on its branches.

To control this disease, you can prune all infected branches, preferably to a healthy collar. This can be done during the colder months when the tree is dormant. If there are infected areas on the trunk of the tree, try to cut out all of the infected wood. Diseased wood should be destroyed, as it could release spores, causing a spread of the disease.

Please reach Arbor Man’s Certified ISA Arborist to handle any serious cases. Call now! 780-485-9663 (WOOD).

Fire Blight

Fire blight is a bacterial disease that affects certain species of the rose family. It is very harmful for crab-apple, apple and pear trees.

Common signs of this disease include leaves turning brown or black, twigs on the tree curling and a sticky ooze seeping from affected areas of the plant. If the disease spreads further, it can infect larger branches, causing destructive cankers to form.

If the bacterial disease survives through the winter, it will resume its spread in the spring. The disease can be carried to other plants by wind, rain, and insects.

To control the disease, remove and burn all infected areas of the tree during the winter season. Also be sure to disinfect any pruning shears that are used. In the spring, remove all new sprouts that appear at the base of the tree. You can also apply certain bactericides.

This highly destructive disease is best controlled through immediate action and constant maintenance. Our professionals at Arbor Man Tree Care would be glad to assist you with the disease control process.

Dutch Elm Disease

Because of the nature of this disease, if you have an elm that has been infected, it most likely cannot be saved. There are some circumstances where the infection can be cut out from the tree, but this is uncommon.

To prevent this disease, proactive measures must be taken. This includes the removal of any infected elms that could spread the disease to other trees. You can also have a fungicide infused into the root flares of each elm tree. One common and highly studied fungicide is Arbotect.

To understand more about Dutch elm disease, it is caused by an aggressive fungus that produces toxins within the tree that eventually cause the inability for water to travel to the crown. Without water, the tree wilts and eventually dies.

The disease is spread by elm bark beetles. These beetles can lay their eggs within infected elms, and then once the eggs hatch, those beetles can distribute the disease to healthy elms. The disease may also be spread by the grafting of root systems, so if elm trees are too close together, they can all quickly become infected.

Cytospora Canker

Although this disease can infect multiple tree species, it is most known for infecting the Colorado blue spruce. This disease becomes destructive in humid conditions, with the ability to kill even mature trees.

A diagnosis of this disease can include seeing cankers form at the base of branches. These cankers can look bluish-white. Often lower branches are affected first.

The disease can be spread by rain and wind, and it infects wounds or weak areas of a tree. A good way to protect from cytospora canker is to avoid injuring trees and to make sure that the surrounding areas around the trees are not too moist. Ongoing tree fertilization can also be helpful.



Cankers are dead areas of bark that can be caused by various fungal infections. Sometimes these cankers can change colors and secrete sap. To avoid the spread of many types of canker-causing fungi, make sure to sterilize all pruning equipment after each use and do not prune in humid conditions. Also, wounds to trees can become infected much more easily than healthy tissue.

Some of the common types of canker-causing fungi include:

  • Botryosphaeria
  • Cytospora
  • Eutypella
  • Hypoxylon
  • Nectria
  • Sphaeropsis

Many of these diseases can be terminal if left untreated. For professional identification and treatment, contact us at Arbor Man Tree Care.

Ash Anthracnose

This fungal disease not only affects ash trees but also maple, oak, and sycamore. To spot this disease, you will notice discoloured or dead spots on the leaves, and the tree may start to lose its leaves in spring.

The spores of this fungus are transmitted by wind and rain. To manage the disease, fungicides are available. You can also fertilize the tree and reduce the use of sprinklers.

Apple Scab

This fungal disease causes lesions to form on the leaves and fruit of apple trees. This disease is not typically lethal but it does affect the tree’s appearance and its fruit. The fungus spreads its spores by surviving on fallen leaves through the winter.

Often with apple scab, you will notice velvety brown spots on both the leaves and fruit. This disease can be treated by disposing of the tree’s leaves once they have fallen and by avoiding watering of the leaves, which can cause the fungus spores to spread.