September 15, 2013
By Ruurd van de Ven
Arborvalley Urban Forestry

Ontario is in a war against the invasive emerald ash borer, which is laying waste to ash trees across the continent, and posing a health and safety hazard to the people who cut them down — including arborists, landscape contractors, farmers, golf course workers, and homeowners.

Discovered in 2002, having arrived from Asia on wood-packing materials in cargo ships and airplanes, the emerald ash borer continues to spread, assisted by people who move infested material like firewood without following regulatory measures imposed by government to contain the damage. The pest has killed millions of ash trees, has few predators, and can withstand Canadian winters.

The Ministry of Natural Resources says that the cost for Canadian municipalities to treat, remove and replace trees affected by the emerald ash borer may reach $2 billion over 30 years. It’s a big problem. But the size of the problem becomes incalculable when you consider the human costs associated with the beetle.

What many people don’t realize about trees infested by the emerald ash borer is that when it comes to removal of the trees, they behave differently than non-infested trees. The underlying science of these differences is not yet completely understood, however, we do know that the inconsistencies increase the risk of injury and death for those who hold the wood-cutting saw blade.

Deadly unpredictability

Diagnosing the structural strength or defects of a tree in preparation to cut it down in the safest way possible, is an inexact science. Professional arborists rely on knowledge and experience gained through formal training programs and related field experience. They know what to look for, and to identify potential hazards before making the cut.

That diagnosis process becomes inexact with infested ash trees. Arborists know how ash trees that have died from natural causes will respond; for example, limbs generally break about three feet away from where they join the trunk. However, the only thing they can count on with infested ash trees is unpredictability. One example is when infested limbs break close to the trunk. It is not possible to know exactly where the break will occur once mechanical forces are applied.

Another danger area is that a tree attacked by EAB will fail at the base much more quickly than if the tree had died from natural causes.

Also, ash trees that have died from beetle infestation can fail in two to four years, unlike dead oak or elm trees, which can remain standing for as many as 15 or 20 years.

This unpredictability can have deadly consequences for the safety of workers and the public, and can cause significant material damage.

Detailed inspection needed

Experienced arborists undertake a detailed inspection process before making a decision on the next steps. If you suspect you have an unhealthy ash tree on your client’s property, here’s a glimpse of what you need to know.  
Don’t automatically blame the beetle. Some of the signs and symptoms of emerald ash borer damage can be attributed to other causes, so residents are urged to call a professional arborist to confirm that the damage is actually caused by the beetle.

Know what the beetle looks like and understand its ways. The adult is dark metallic green in colour, a half-inch long and 1/8 inch wide. Ontario Ministry of Natural Resources has published, A Visual Guide to Detecting Emerald Ash Borer Damage at

Keep an eye on the canopy. The beetle works by destroying tissues under the bark that conduct water and nutrients, resulting in yellowing leaves, a thinning canopy, dead branches and cracks in the bark.

Adult beetles leave notches on the edges of an ash tree’s leaves and D-shaped holes in the trunk, about 1/8 inch in diameter when they exit the tree in June. Under the bark, you will see S-shaped tunnels, known as galleries, made by larva feeding on the wood. Professional assessments of the stem require special training and may include trunk sounding and the use of special tools of devices used by a trained arborist.

What if tree is infested?

  • Don’t cut until you know for sure. If the tree is lightly infested, it may be possible to treat and save it using pesticides. Heavily infested trees must come down and the wood disposed of according to federal regulations. Visit the Canadian Food Inspection Agency website for updates on regulated areas. In some cases, trees on private property are protected and regulated under the provisions of municipal by-laws, in which case you should contact your municipal office before treating or cutting the tree.
  • Help prevent further infestation by observing Canada’s regulations restricting the movement of infested material.