Among the variety of pests that can cause significant harm to trees, one species in particular is the primary culprit for damage to ash trees are emerald ash borers, scientifically known as agrilus planipennis. Knowing how to identify damage caused by these particular pests can help you address the issue, protect your trees, and prevent future infestations.

A Quick Look at Emerald Ash Borers

In a 2014 study, emerald ash borers were termed as “the most destructive and economically costly forest insect” since its discovery in North America. Known for its metallic green back and an emerald green underside, it is difficult to see with untrained eyes.

Emerald ash borers grow from 8.5 to 14.0 mm long and 3.1 to 3.5 mm wide which makes it invisible to the eye. Larvae are even more difficult to spot because they penetrate the bark, eventually starving the tree and killing it.

Immature emerald ash borers feed on the foliage, causing small slits on the surface of leaves. They lay their eggs on the branches where they stay until they grow into larvae. The larvae can grow until 2 to 5 cm long and its S-shaped gallery extends throughout its life span. It forms a 6 mm S-shaped path filled with a fine brownish coating.

Importance of Ash Trees

Causes and Treatments of Emerald Ash Borer Infestations

Emerald ash borers can infest any tree species, but they are commonly seen in ash trees. Ash trees account for the largest number of forest trees in Canada. Commonly lining streets and woodlots, ash trees play a vital role in the country’s landscape.

In addition to their aesthetic value, ash trees also serve as the main raw material for producing furniture, hardwood flooring, baseball bats, hockey sticks, and other materials that require high wood strength. This is why the presence of these pests in ash trees are a major concern in Canada.

How to Spot Emerald Ash Borers on Ash Trees

While it may be a challenge to detect the presence of emerald ash borers due to their size and behavioural patterns, it isn’t impossible. You can identify an infestation by looking for insect signs and/or tree symptoms.

Causes and Treatments of Emerald Ash Borer Infestations

  • Insect Signs
    • Cuts on the tips of the leaves – Adult emerald ash borers leave tiny cuts on the edges of foliage when they feed. These are the most noticeable signs of an ash borer infestation.
    • Gallery formation – When the larvae grows between the bark and sapwood, they move up and down the tree bole or branch, creating an S-shaped zig-zag formation called a “gallery”.
    • Unusual shape formation – As emerald ash borers continue to damage the tree, you may notice D-shaped holes in the bark and canopy. These are traces left by the insects as they move to other parts of the tree.
    • Ragged strips on the bark – Birds and other animals can create ragged strips on the bark when feeding on insects in or on the tree. Inspect stripped areas. If you see the S-shaped galleries produced by the emerald ash borer larvae, the tree is infested.

Causes and Treatments of Emerald Ash Borer Infestations

  • Tree symptoms
    • Discolouration – If the uppermost leaves have lost colour and the crown has lost density, the ash tree may be infested with emerald ash borers.
    • Development of sprouts – Ash trees develop sprouts or epicormic shoots from the roots, trunk, or branches as a defense mechanism to aid in transporting nutrients. As the infestation worsens, the tree gradually starves to death.
    • Heavy seed production – When a tree is in distress, it sometimes flowers and produces more seeds as a survival mechanism. This can also be a symptom of emerald ash borer infestation.
    • Bark deformities – Vertical splits or cracks on the surface of the trunks are common signs that a tree is infested. The bark cracks are usually 5 to 15 cm long and on young trees, the bark turns pinkish brown and dries.

Use these signs to uncover an infestation before it becomes unmanageable. You can check your ash trees yourself before calling a professional.

Causes and Treatments of Emerald Ash Borer Infestations

Causes and Treatments of Emerald Ash Borer Infestations

Over the years, scientists have been actively looking for solutions that can mitigate the damage emerald ash borers can cause. While there are various treatments available, the early detection of emerald ash borers is critical in saving ash trees. Preventing them from finding their way into trees, impeding further damage in infested areas, and controlling the population of these insects are the best solution.

To this end, tree owners should know the types of activities that increase the risk of an emerald ash borer infestation. Prevention, after all, is better than the cure. Keep these pests at bay and save your ash trees from damage by avoiding the following activities:

  • Transporting infested firewood in a tree populated area
  • Moving ash woods, logs, branches, and nursery stock from one place to another
  • Spraying insecticides, which causes insects to relocate and start infesting another tree
  • Importing firewood from a country with high infestation levels

Causes and Treatments of Emerald Ash Borer Infestations

There are multiple treatment options available to help save ash trees from emerald ash borer infestations including:

  • Soil-applied treatments, which can be applied annually to treat trees no more than 15 inches in diameter
  • Trunk-injection treatments, which are used to treat trees with a diameter greater than 15 inches and reapplied every two years to
  • Systemic basal trunk sprays, which are sprayed annually to treat the trees’ vascular system

While you can apply the soil-applied treatments yourself, the more effective solutions (e.g. trunk-injection and systemic basal trunk treatments) require a licensed professional. Although these treatments can be costly, treating your trees is cheaper compared to replacing them.

It’s time to check your ash trees for possible infestation. If you suspect an infestation or you notice the signs and symptoms emerald ash borer presence, consult the nearest expert as soon as possible. Get a head start and nip the infestation in the bud with help from a tree care professional. Contact Dave Lund Tree Service and Forestry Co Ltd. to assess your trees for possible risks. We have over 40 years of experience under our belt and have provided services in various areas in Ontario, especially in the York Region. Call us today at (905) 884-0511 or at (905) 775-1020 and let us help you solve your ash tree pest.