Ash Borer: Identifying an Infestation, Treating or Felling the Tree

An ash tree infested with the emerald ash borer will not recover on its own. The decision is made by examining the tree’s crown: as long as the dieback is mild, an injection can keep the ash tree alive; once it becomes more severe, cutting it down becomes the only safe option.

Key Points

• The emerald ash borer (Agrilus planipennis) typically destroys 99% of the ash trees in a region within 8 to 10 years after it becomes established there.
• The insect has been present in North America since 2002 and has been detected in parts of six Canadian provinces.
• The first signs appear at the top of the tree, often one to two years before the owner notices anything.
• Four insecticides are registered in Canada for use against this pest, including TreeAzin, the only one of natural origin.
• Once the dieback of the crown is well advanced, the process is irreversible: treatment is no longer effective.
• It is prohibited to remove ash products or heating materials from a regulated area without authorization from the CFIA, and municipal subsidies are available for tree removal.

Why Does This Tiny Insect Kill Such Large Trees?

The emerald ash borer is a beetle native to Asia that arrived near Detroit and Windsor in 2002. Natural Resources Canada notes that most North American ash trees have no natural defenses and that the beetle typically kills 99% of ash trees within 8 to 10 years in areas where it becomes established.

It is not the adult beetles that kill the ash trees, but their larvae. The larvae burrow winding tunnels just beneath the bark of the trunk, into the tissue that carries sap. When these tunnels eventually connect, sap flow is cut off and death becomes inevitable, as explained by the Quebec Council on Invasive Alien Species. This is why an ash tree may appear healthy one year and collapse within two growing seasons.

Wilting always begins at the top of the crown: this is the first visible sign from the ground.

Signs of infestation to watch for on your property

The emerald ash borer attacks ash trees , starting at the top. As a result, it’s often too late to detect the infestation from the ground. Here’s what a homeowner can actually see.

Please note: Drought, frost, and other pests can cause similar symptoms. The CQEEE emphasizes this point in its fact sheet on signs of infestation. A visual assessment of the soil is no substitute for a close inspection of the tree canopy by an arborist.

The winding tunnels burrowed beneath the bark block the flow of sap. This is the most reliable sign.

Treat or Cull: How the Decision Is Made

The rule of thumb is simple. An ash tree with a crown that is still full and vigorous is a candidate for treatment. An ash tree whose crown is mostly dead must be cut down, because its wood becomes brittle and dangerous to climb very quickly.

The calculation is not only biological; it is also economic. The CQEEE cites an estimate of $150 to $250 per large tree (DBH greater than 30 cm) for an injection, a cost that, according to Thompson’s research published by Natural Resources Canada, remains equivalent to or lower than cutting followed by replacement in urban areas. These are estimates drawn from the literature, not a fixed price: each case must be assessed on-site.

The condition of the tree crown determines the most realistic course of action: injection, monitoring, scheduled pruning, or emergency felling.

What an Ash Borer Treatment Actually Does

There are four registered products in Canada: Acecap, Confidor, Ima-Jet, and TreeAzin, as indicated on the CQEEE treatment page. TreeAzin is the only one of botanical origin: its active ingredient, azadirachtin, is extracted from neem seeds and is applied via microinjection into the active sapwood.

Its mode of action explains why early intervention is necessary. Azadirachtin prevents young larvae from molting and reduces the fertility of adult females. The solution therefore protects a tree that is still functional—one capable of circulating sap and distributing the insecticide. In an ash tree whose vascular channels are already destroyed, the active ingredient cannot reach any part of the tree. Treating several neighboring ash trees at the same time also helps slow the spread throughout a neighborhood—an approach that the Quebec Federation of Forest Producers also applies to private woodlots.

Injections must be administered by a trained applicator during the growing season and repeated as long as the outbreak is active in the area.

Regulations, permits, and grants: Don’t skip this step

Cutting down an ash tree is almost never permitted without authorization in Quebec. Each municipality regulates the process through bylaw, and many cities require a permit even before the first cut is made. The rules applicable in Granby and other cities we serve are detailed by municipality, as they vary from one place to another.

Some cities go a step further and offer a subsidy. Longueuil, for example, maintains a financial assistance program for the removal of ash trees on private properties. For its part, Quebec City is documenting the extent of the emerald ash borer’s impact on its urban forest. Always check the program in effect for the current year before planning any work, as funding allocations and eligibility criteria are subject to change.

The cut timber does not leave the restricted area

This is the most common mistake—and the one with the most serious consequences. The pest is primarily spread through logs and firewood transported by humans. The CFIA prohibits the movement of ash products and firewood out of a regulated area without prior authorization, including for private use such as taking them to a cabin or campground. Details of the requirements can be found in the official fact sheet on the emerald ash borer, and the Agency also provides a broader reminder of the dangers associated with transporting firewood.

The map of the zones is changing, too. In April 2026, the CFIA announced an expansion of the regulated zone, specifically targeting the Bonaventure and Charlevoix-Est RCMs as well as the city of La Tuque. A tree care contractor must manage tree trimmings in accordance with these rules: this is a part of the job that the property owner doesn’t see.

A Realistic Plan for a Homeowner

• Identify your ash trees. Many homeowners are unaware that they have one. A tree inventory can identify it in a single visit.
• Have the tree crown assessed before deciding between pruning and cutting it down, ideally once the leaves have emerged.
• Treat it early, or forget about it. Un frêne en dépérissement avancé ne se récupère pas.
• Schedule non-emergency surgery. Un frêne mort coûte plus cher à retirer et présente un risque réel de chute de ramure.
• Replace it with another tree species to avoid re-establishing a vulnerable monoculture.

This is exactly the type of work covered by our services for managing dead ash trees, tree care, and tree removal in the Montérégie and Estrie regions. For a free estimate tailored to the actual condition of your ash trees, please contact us through the contact page.