Emerald Ash Borer in Hamilton: Identification, Risk, and Removal

Published March 2026  |  Hamilton Tree Pros  |  8 min read

The emerald ash borer (EAB) has been the most destructive invasive forest pest in North American history. Since its detection in Ontario in 2002, it has killed hundreds of millions of ash trees across the continent. In Hamilton specifically, the losses have been severe: the City has removed thousands of ash trees from public property alone, and ash trees on private land throughout the city continue to die every year.

If you have an ash tree on your Hamilton property — or suspect you do — understanding EAB, recognizing the signs of infestation, and knowing when treatment is still viable vs when removal is the only option is information you need now, not after the tree falls on your fence.

What Is the Emerald Ash Borer?

The emerald ash borer (Agrilus planipennis) is a small, iridescent green beetle, about 8–14 mm long, native to northeastern Asia. In its native range, ash trees and the beetle co-evolved — trees have natural defences, and the beetle population is kept in check by local predators and parasitoids.

In North America, ash trees had no such co-evolved defences. EAB arrived — likely in solid wood packing material from Asia — and found an entire continent of completely vulnerable host trees. It attacks all true ash species (Fraxinus spp.), including the white ash, black ash, green ash, and blue ash that are common throughout southern Ontario's urban forest.

EAB kills by disrupting the tree's vascular system. Adult beetles lay eggs in bark crevices; larvae hatch and bore into the cambium layer just beneath the bark, feeding in winding S-shaped galleries that girdle the tree. Once the galleries disrupt water and nutrient flow around the trunk's full circumference, the tree dies — typically within 3–5 years of initial infestation in untreated trees.

Hamilton's EAB Situation

EAB was first confirmed in the Hamilton area in the early 2010s. By the mid-2010s, Hamilton had lost a substantial portion of its urban ash canopy. The City of Hamilton's urban forestry program has been removing and replacing EAB-killed street ash trees on a rolling basis for over a decade — a process that continues today because ash mortality is ongoing and the replacement trees are a fraction of the size of what was lost.

Private property ash trees have had less systematic attention. Many were treated by homeowners; many more were not. The result is that Hamilton still has a significant population of dying or dead ash trees on private land — some still standing, some already structurally compromised, many with owners who don't know what they have.

How to Identify an EAB-Infested Ash Tree

The challenge with EAB is that visible symptoms appear late — often 2–4 years after initial infestation. By the time you can clearly see the signs from the ground, the infestation is well-established. Here's what to look for:

When to Treat vs When to Remove

This is the most important and most misunderstood decision for Hamilton homeowners with EAB-affected ash trees. Treatment is effective — but only within a specific window.

Treatment is viable when:

• The tree has less than 30–40% canopy dieback — still has substantial healthy crown remaining
• The infestation is early to moderate — D-shaped exit holes present but tree not yet severely girdled
• The tree is otherwise structurally sound and in good health (not weakened by other disease, rot, or mechanical damage)
• The tree has genuine value — aesthetic, shade, heritage, or property value — that justifies ongoing treatment cost

Two main treatment options

TreeAzin (azadirachtin): A systemic insecticide derived from neem oil, injected directly into the trunk. TreeAzin is the primary certified-organic option and has been widely used across Ontario. It's injected every 2 years, typically in spring or early summer when the tree is actively moving fluids. Cost: approximately $150–$400 per treatment depending on tree diameter, applied by a licensed applicator.

Emamectin benzoate (TREE-äge): A synthetic insecticide also administered by trunk injection. Emamectin is considered the most effective EAB treatment option currently available, providing 2–3 years of protection per injection. It's approved for use by licensed applicators in Canada. Cost: comparable to TreeAzin, sometimes slightly higher per treatment but with longer protection intervals.

Treatment is NOT viable when:

• The tree has more than 50% canopy dieback — the damage is too extensive for the tree to recover meaningful function
• The tree is dead or nearly dead — systemic treatments cannot be translocated through a tree that has lost its vascular function
• Significant structural wood decay is already present — the tree is a hazard regardless of EAB treatment success
• The cost of ongoing treatment exceeds the value the tree provides

The Structural Risk of Dead Ash Trees: Why Urgency Matters

This is the aspect of EAB that most urgently affects Hamilton homeowners with a dead or dying ash on their property: ash trees killed by EAB become structurally dangerous very quickly compared to other species.

Unlike oak, maple, or most other hardwoods that remain structurally sound for years after death, ash wood degrades rapidly once the tree dies. The wood dries and becomes extremely brittle. Branch attachment points — already weakened by the loss of living cambium tissue — fail with relatively minor loads. A wind event that would cause no damage to an equivalent living tree can bring down large branches or the entire crown of a dead ash.

This creates two practical problems for Hamilton homeowners:

1. Liability. A dead ash tree on your property that drops a limb onto a neighbour's car, fence, or — critically — a person, is a foreseeable hazard event. Insurance adjusters are aware of EAB and its structural implications. A dead ash that has been standing for years is difficult to characterize as an unexpected or unforeseeable event.
2. Removal cost. Removing a structurally compromised, brittle dead ash is significantly more expensive than removing a living tree of the same size. The wood cannot be safely pulled and lowered in sections; branches detach unpredictably; climbing is dangerous or impossible. Contractors must use cranes or complex rigging, adding substantially to the cost.

What Ash Tree Removal Costs in Hamilton

The EAB Permit Question

EAB creates a specific complication around Hamilton's tree removal permit requirements. Hamilton's by-law requires a permit to remove trees above the size threshold — but also includes an exemption for dead trees. Dead ash trees killed by EAB fall into a grey area that arborists and by-law officers navigate regularly.

The practical guidance: if your ash tree is confirmed dead by EAB and meets the by-law's definition of a dead tree, the permit exemption may apply. However, "confirmed dead" is a legal determination under the by-law, not just a homeowner's observation. Get written arborist confirmation of the tree's condition before removal. This documentation protects you if the exemption is ever questioned, and it's the same documentation you'd need to defend against a fine.

For ash trees with significant but incomplete dieback — dying but not yet dead — the permit requirement applies. Don't assume that because EAB is the cause, the city's permit requirement doesn't apply.