Common Tree Pests in Calgary
Calgary’s trees provide shade, beauty, and value to homes and neighborhoods—but they also face threats from pests that can weaken or even kill them if left unchecked. Some infestations cause visible damage right away, while others work quietly beneath the surface until the problem becomes severe. The sooner you can spot the signs of pests, the more likely it is you can save your tree and prevent the issue from spreading.
Why Tree Pests Are a Serious Problem
Tree pests don’t just damage leaves or bark. By feeding on essential tissues, sucking sap, or tunneling through leaves, pests weaken trees from the inside out. This stress reduces a tree’s ability to photosynthesize, makes it more susceptible to disease, and increases the likelihood of structural failure.
Unchecked infestations can turn otherwise healthy trees into hazards, creating risks for your property and neighborhood. For Calgary homeowners, regular monitoring and professional care are the best defenses.
Common Tree Pests in Calgary
While Calgary doesn’t face as many pest problems as warmer climates, there are several common offenders that every homeowner should know about:
Aphids – These small, soft-bodied insects cluster on leaves and stems, sucking sap from trees. Symptoms include curled or distorted leaves, yellowing, and a sticky substance known as honeydew, which often leads to black sooty mold.
Spider Mites – Almost invisible without close inspection, spider mites thrive in Calgary’s hot, dry summers. They leave fine webbing on leaves and cause speckled or stippled foliage. Heavy infestations can cause significant canopy thinning.
Leaf Miners – These pests tunnel inside leaves, creating distinctive winding trails. While often cosmetic at first, severe infestations weaken trees by reducing their ability to produce energy.
Black Knot Fungus – Though technically a fungal disease, black knot spreads much like a pest. It causes black, tar-like swellings on branches, especially in Mayday and Schubert chokecherries. If left untreated, it spreads rapidly and kills affected limbs.
Emerald Ash Borer (EAB) – The most concerning pest threat across Canada. While not yet confirmed in Alberta, EAB has devastated ash trees in many provinces, killing tens of millions. EAB larvae feed beneath the bark, cutting off nutrient flow. By the time visible symptoms like canopy thinning or D-shaped exit holes appear, it’s often too late.
Knowing these pests and their signs gives you a head start in protecting your trees.
Why DIY Treatments Often Fail
When pests appear, many homeowners reach for chemical sprays or treatments from the hardware store. Unfortunately, DIY approaches are often ineffective—or worse, harmful.
Non-Target Damage: Many sprays kill beneficial insects like ladybugs and pollinators along with the pests.
Short-Term Relief: Over-the-counter treatments rarely address the root of the problem, leading to recurring infestations.
Environmental Risks: Excess chemicals can leach into soil, harm waterways, and disrupt nearby plants.
Misdiagnosis: Without training, it’s easy to mistake one pest for another and apply the wrong treatment.
What looks like a quick fix often ends up stressing trees further while leaving the real problem unsolved.
The Role of ISA Certified Arborists
An ISA Certified Arborist brings the expertise needed to accurately diagnose and treat tree pest problems. Unlike general contractors, arborists specialize in tree biology and care, ensuring that treatments strengthen your tree rather than harm it.
Certified arborists can:
Accurately Identify Pests – Distinguishing between similar-looking problems to target the real issue.
Recommend Safe, Effective Treatments – Using targeted products only when necessary.
Implement Integrated Pest Management (IPM) – A holistic approach that minimizes chemical use by combining pruning, biological controls, and soil care.
Monitor Long-Term Health – Regular inspections to catch problems before they become severe.
Balance Treatment with Ecology – Protecting beneficial insects and the broader urban ecosystem.
With professional guidance, you don’t just eliminate pests—you restore balance and resilience to your trees.
Integrated Pest Management: A Smarter Solution
Instead of relying solely on chemicals, arborists often recommend Integrated Pest Management (IPM). This science-based approach focuses on prevention, monitoring, and minimal intervention.
Common IPM strategies include:
Pruning – Removing infested or infected branches to stop spread.
Encouraging Beneficial Insects – Supporting natural predators like ladybugs that feed on aphids.
Targeted Treatments – Applying environmentally friendly products only when necessary and in precise locations.
Soil and Nutrient Care – Strengthening trees so they are naturally more resistant to pests.
IPM protects your trees long-term while minimizing harm to the environment.
Protecting Your Trees Before It’s Too Late
Pests are easiest to manage when caught early. A small cluster of aphids or a few black knot swellings are manageable; a full-scale infestation may require major pruning or even removal. That’s why regular monitoring and professional inspections are so important.
For Calgary homeowners, scheduling annual or bi-annual inspections with a Certified Arborist ensures pests are caught before they become serious threats.
A Healthy Tree Is a Strong Tree
Strong, well-cared-for trees are naturally more resistant to pests. By combining regular inspections, proper watering, mulching, and fertilization, you create conditions that make your trees less appealing to insects and fungi. Think of pest management as part of a bigger picture of holistic tree care.
Healthy trees add shade, beauty, and value to your property. Monitoring them regularly and acting quickly when pests appear is the key to protecting that investment.
