They say that trees are the lungs of the Earth. A source of inspiration and elegance, they beautify the landscape and enhance the appearance of our neighborhoods. They provide us with coolness and shade in the summer, retain moisture, help stabilize the soil and contribute to our urban ecosystems.

But beyond that, trees are also living organisms. And as such, they aren’t immune to diseases. Even so, trees are robust, demonstrating strong resistance to the numerous maladies that can attack them. The good news is that, in this day and age, botanists and arboriculturists can easily identify the different diseases that affect trees and propose the appropriate care and preventive measures.

What are the main diseases affecting trees in Quebec?

The most common tree diseases are caused by fungi, insects, bacteria and wounds of various origins.

While there are many different types of diseases that can attack trees, here’s a list of the ones that are most common in Quebec.

Powdery mildew – This is a fungal disease that attacks the outer layer of the leaves, covering them partially or completely with white spots. The fungus only affects the growth of the tree and disappears once the leaves fall. The best treatment is to avoid watering in the evenings and to increase the branches’ exposure to the air through strategic pruning.

Beech bark disease – This is an exotic disease. An insect called a cochineal bores holes in the bark. This allows two pathogenic fungi (Neonectria faginata and Neonectria galligena) to infect the wounds. As a result, cankers in the form of oozing blisters can appear, as well as a dark liquid discharge, in the case of a severe infestation. This disease can be treated by spraying or brushing the bark with dormant oil.

Dutch elm disease – This incurable disease afflicts the elm trees of Eastern Canada. The disease progresses very quickly, causing the leaves to wilt and turn brown in the summer, forcing them to fall prematurely. It’s essential to prune the tree and apply pesticides.

White pine blister rust – This fungal disease is characterized by the appearance of orangish patches that form on the trunk. Cankers are also visible. The result is strangulation of the trunk, accompanied by a resinous discharge. The damage can be mitigated by removing the affected bark.

Arborvitae leafminer – Commonly called cedars in Canada, arborvitae trees or thujas are coniferous trees that are frequently assaulted by caterpillars. These larvae ravage the tips of the new shoots, turning them yellow and causing them to wither. The current year’s shoots must be cut off right away, and the tree must be sprayed with dormant oil.

Maple tar spot and rust mites – Toward the end of summer, you will often see maple leaves speckled with black spots. This is caused by a fungal disease for which there’s really no known cure. As for rust mites, these are tiny arachnids that feed on sap. However, they won’t harm the tree.

There are numerous other diseases that can affect our trees here in Quebec, but it would be tedious to name them all. The emerald ash borer is one of the most well-known, but other common ailments include the birch borer, Fletcher scale, witches’ broom disease, and blossom blight, not to mention the wide range of damage caused by animals. At Emondage SBP, we can give you expert advice to help you maintain your trees in good health. Contact us for more information!

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