Common Tree Pests in Calgary: How to Identify and Manage Them

Even the healthiest trees can fall victim to insect pests, especially when stressed by drought, chinooks, or improper pruning. Calgary’s climate supports a variety of insects that damage leaves, bark, roots, and branches. When left untreated, these pests can weaken a tree, reduce growth, and contribute to long-term decline.

At Calgary Tree Care, our ISA Certified Arborists diagnose pest issues throughout the city. This guide outlines the pests most commonly affecting Calgary trees, the signs to watch for, and what homeowners should do when an infestation is suspected.

Why Pest Problems Are Common in Calgary

Calgary’s pest pressures increase due to several factors:
• Drought cycling weakens tree defences
• Chinook stress damages buds and bark
• Dry summers favour certain insects
• Urban environments limit natural predators
• Overcrowded plantings encourage pest spread

Understanding these pressures helps explain why even well-maintained trees can be affected.

1. Aphids

Aphids are one of the most widespread pests in Calgary, feeding on leaf sap and causing distorted growth.

Signs of aphids include:
• Sticky residue (honeydew) on leaves or surfaces below
• Curling or disfigured leaves
• Sooty mould on foliage
• Small clusters of insects on stems or leaf undersides

Aphids commonly affect maples, ashes, lindens, and fruit trees.

2. Birch Leafminers

These pests are highly common in Calgary’s birch trees. Leafminers burrow within leaves, causing brown blotches and early leaf drop.

Symptoms include:
• Brown, papery patches inside leaves
• Early defoliation
• Thinning canopy
• Reduced vigour year after year

Untreated leafminer infestations often worsen annually.

3. Cottony Psyllid (on Swedish Columnar Aspen)

Swedish columnar aspens are extremely popular in Calgary—and extremely vulnerable to this pest.

Indicators include:
• Leaf curling
• Sticky residue
• Cotton-like clusters
• Defoliation on upper branches
• Stunted growth

Repeated infestations weaken aspens over time.

4. Spider Mites

Common during hot, dry Calgary summers, spider mites feed on leaf tissue.

Signs include:
• Fine webbing on leaves
• Speckled or stippled foliage
• Brown or bronze discolouration
• Premature leaf drop

Mites often affect spruce, pine, and ornamental species.

5. Scale Insects

Scale insects latch onto branches and suck nutrients from the tree.

Symptoms include:
• Raised bumps on bark or twigs
• Honeydew and sooty mould
• Branch dieback
• Declining vigour

Scale insects can be difficult to detect until damage is advanced.

6. Poplar Borers

These insects attack poplars, aspens, and cottonwoods—common species throughout Calgary.

Warning signs:
• Sawdust-like frass at the base
• Holes in bark
• Dieback in affected branches
• Weak or brittle limbs

Borers often target stressed or water-compromised trees.

7. Mountain Pine Beetle (Occasionally)

While less common in Calgary than in the foothills, pine beetles can still impact urban pines.

Indicators include:
• Boring holes
• Pitch tubes (sap blobs)
• Needle discolouration
• Rapid decline

Early detection is crucial for containment.

How to Tell if a Pest Problem Is Serious

Pest damage becomes concerning when you notice:
• Repeated yearly infestations
• Canopy thinning
• Early leaf drop
• Branch dieback
• Multiple pest species on the same tree
• Signs of decay or structural stress
• Slow or stunted new growth

Trees already stressed by drought, pruning errors, or soil issues are especially vulnerable.

Why Pest Identification Matters

Different pests require different approaches. Misdiagnosis often leads to ineffective treatments or unnecessary removals. Professional arborists consider:
• Pest species
• Infestation severity
• Time of year
• Tree species
• Long-term health and structure
• Environmental conditions

Correct identification ensures the tree gets the right care at the right time.

What Homeowners Should Do if They Suspect Pests

• Avoid spraying chemicals without proper diagnosis
• Document symptoms and progression
• Check multiple sides of the tree
• Look for patterns (upper canopy vs. lower branches)
• Contact an arborist for an assessment

Many pest issues are manageable if caught early.

Why Choose Calgary Tree Care

Our ISA Certified and TRAQ Qualified Arborists have more than 15 years of experience diagnosing Calgary’s most common pest problems. We provide:
• Pest and disease identification
• Tree health assessments
• Evidence-based treatment recommendations
• Structural pruning to reduce stress
• Risk assessments for compromised trees
• Honest guidance focused on long-term recovery

We help homeowners take proactive steps to protect their trees.

Schedule a Pest Assessment

If you suspect your tree may have a pest problem, contact Calgary Tree Care for a professional evaluation. Early detection is the key to preserving tree health and preventing decline.