Ash Borer – FACTS

If you’re reading this, your Ash Tree is probably already dead.

It’s not my fault- blame cheap imports. Emerald Ash Borer (Agrilus planipennis) is a green beetle native to Asia. Introduced to North America in the 1990’s via wooden pallets, it is estimated to have killed 50-to-100 million Ash trees so far, and threatens to kill most of the 7.5 billion Ash trees in North America.

The Emerald Ash Borer (EAB) is a destructive pest that threatens the survival of the Ash (Fraxinus) species in North America.  The effects are terrible – I’ve seen them.

Brown staining – telltale symptom of Emerald Ash Borer.

I was visiting a friend in Grand Ben, Jesse, a very capable arborist and owner of TriCountry Tree Service, and he showed me, from his property just outside of town, how the woodlots have changed since the coming of the Ash Borer.

It was remarkable.  In the middle of the Summer, not less than 20% of the tree line was brown.  As I drove back, I began to pay more attention to the trees- the severity of the devastation lessening as I got closer to Guelph.

EAB has been compared to the Chestnut Blight and Dutch Elm Disease in its potential to damage North American Forests.

I think it may be worse. What makes EAB particularly dangerous is its tendency to target all species within a genus- in other words, it will attack White Ash, Green Ash, Black Ash and even Blue Ash which, despite its resistance in the short-term by forming callous tissue against EAB, it eventually succumbs.  Unlike Elm, where the trees can live to be thirty years, spread their seeds, and carry on for thirty years prior to infestation, EAB kill old and young trees.  Destroys them before they can seed.  Destroys them quickly.

It is terrible.

Consider the following:

  • EAB has killed some 50-100 million trees in North American since the mid-1990’s.
  • In a typical town/small city, 60-70% of Ash trees will die with 8-11 years of infestation. Eventually, all Ash trees in an infested zone will die.
  • The prevalence of Ash in the urban forest, combined with the destructiveness of EAB, has resulted in considerable reduction in the tree canopy of many towns (20-25%). Some studies have shown a rise in pollution-related illnesses and deaths where urban areas have been severely deforested as a result of EAB.

I suspect my tree has Emerald Ash Borer Infestation. Now what?

Emerald Ash Borer infestation will show certain symptoms (in the tree itself) as well as signs, or physical evidence, of the presence of the Ash Borer.  Let’s start with symptoms- if you recognize any of the following in one of your Ash Trees, your tree may be at risk.

Dead White Ash at Guelph Arboretum. Another proud tree laid low by EAB.

Potential Indicators ( well, there’s a chance… )

  • Crown dieback. You may see dead branches or sparsely leaved branches in the upper canopy, or leaves that appear to lack vigour or demonstrate chlorosis (yellowing).
  • Weird patches of light-coloured, inner bark.
  • Epicormic sprouting, on an Ash, is demonstrative of a stressed tree. It’s often called <i>staghorning</i> due to the aggressive growth of shoots. Because of the disruption of nutrient flow as a result of EAB larvae, the tree will respond by producing shoots at its trunk, often in the vicinity of the larval feeding galleries.
  • Bark splitting, where a tree (esp. Blue Ash) attempts to compartmentalize the damage being done by the feeding larvae. One can inspect the wound, and often see larval galleries within the tree.
  • Woodpecker activity increases, as woodpeckers aggressively bore into the wood to get at the larvae. Extensive flecking is physical damage done to the tree as a result of woodpecker boring.

Positive Indicators ( yup, you got EAB )

  • D-shaped emergence holes, as larvae bore out through the bark of the tree.
  • S-shaped larval galleries, that wind inside the bark.  This is the larval feed bath, and is often packed with sawdust.
  • Presence of larvae. Larvae are cream-colored, slightly flattened  and have pincher-like appendages at the end of their abdomen. Mature larvae reach 1 1/2 inches in length and all larvae are found feeding beneath the bark.
  • Adult beetles are a very distinct metallic green and are approximately 3/8 inch in length.

Darn it- I’m pretty sure my tree has been infested with EAB. What are my next steps…

Phone an arborist. These are dangerous take downs.  We’ve found that the wood strength degrades quickly, and there have been reported weaknesses on stem tissue approximately 15 feet above the ground.  Tie-In Points are significantly compromised, requiring specialized, redundant climbing technique.  Straight felled trees are more prone to barber-chairing <i> (think tree-as-baseball-bat-hitting-under-chin…)</i>

It is important to remove the tree immediately- within the season. The EAB lifecycle will completely kill an Ash tree after four years, and if the tree is allowed to persist another year, the wood becomes brittle and failure-prone, and thus a hazard to property and people.  For the climbing arborist, especially where the tree is out of reach of a boom or skyjack, the tree may become very dangerous and problematic to remove. Oh, and very expensive.

Is there hope for our Ash trees?

A tentative yes.  The United States Forestry Service has introduced a form of Asian, parisitoid wasp into the wild. Tetrastichus planipennisi is the natural predator of EAB in China, and its release in certain areas of the United States has demonstrated its ability to keep EAB populations below a threshold level, at which Ash populations are not affected. This is a potential biological control of EAB on a grand scale, to prevent the complete extinction of the Fraxinus species from the Forests of North America.  Another hope is that there are ‘resistant’ Ash that possess a genetic mutation that will allow them to survive, and eventually to re-seed the Ash population.  In Europe, they’ve found that there is about a 5% resistance rate of some Ash to EAB- although that doesn’t help you if your tree is not one of the 5%, and is in your back yard.

If Ash Borer doesn’t scare you enough, here some others…

Black Knot ( Apiosporina morbosa )
Affects Prunus family such as Chokecherry, Mayday and Plum.


Black Knot (Apiosporina morbosa) is a fungus that affects Plum trees  (Rosacaea Prunus spp ). In the local area, these would commonly include Chokecherry ( Prunus virginiana ) and Mayday ( Prunus padus ). When you see that a branch has a large, black growth on it, black knot may have already infected your tree.  Black knot is a localized fungus, and will cause dieback in the infected branch.  Black knot will continue to spread along living tissue within the tree. On infecting the subtending branch, it will girdle that branch, thus contributing to further dieback. Black knot fungus matures in the Spring the year following infection.  At maturity, the spores are released into the air in response to rain.  These spores settle on new, or green, shoots, and a wet period of 6 hours is all that is required to infect the shoot.


Hypoxylon Canker ( Hypoxylon mammatum ) 

Affects Populus family including Balsam Poplar and Trembling Aspen.


Hypoxylon mammatum is one of the most destructive diseases of Trembling Aspen (P. tremuloides). In the Great Lakes Forest Region, for example, it is estimated that 12% of Aspen is infected at any given time, resulting in annual tree growth losses of 30% of net tree growth for this species.

Other affected Poplar species are Big Tooth Aspen (P. grandidentata) and rarely on Balsam Poplar (P.balsamifera) and White Poplar (P. alba ).

One first recognizes hypoxylon canker in the foliage.  Affected trees will show undersized yellow leaves, or dead branches with brown leaves still attached. The bark about the canker can appear yellow-orange to orange-brown. In the spring and summer of the second year, the dead bark will appear mottled, and the fungal infection will raise the bark, which will begin to slough off. Infection occurs when these fungus are active, in the second year, during the summer, and requires rainy, wet weather to activate the spores.


Dutch Elm Disease 

Affects Ulmus family including American and Manchurian Elms.


Dutch Elm Disease is a well known, insect-borne disease that could be devastating to the rare and beautiful American Elm (Ulmus americana ) that line the streets of Edmonton. While the disease has been contained outside of Alberta, any neglect of pruning bans and firewood imports could put our elms at risk.  Dutch Elm Disease is a fungal infection, whereby fungal spores of