On July 21, the emerald ash borer was detected on the Island of Montréal for the first time, in the Mercier-Hochelaga-Maisonneuve district near the port. This small Asian beetle is a threat to all species of ash; it can kill a healthy tree in three to four years.
The emerald ash borer (Agrilus planipennis) has a narrow, metallic emerald-green body. It is 8–13 mm long and its protruding eyes are black or bronze. This exotic insect poses no danger to humans, but it is a serious threat to the 45,000 ash trees in Montréal, representing 20% of the trees lining the city’s streets.Accidentally introduced to North America in the 1990s, the emerald ash borer was first detected in Ontario and Michigan in 2002. Because it has no predators on this continent, it has multiplied quickly. Its spread has been accelerated by the movement of firewood. Since its arrival, this pest has destroyed millions of ash trees across the US and Ontario. In North America, the emerald ash borer attacks all species of ash but does not damage other types of trees. Ash trees are easy to recognize; their compound leaves grow opposite each other along the branch, with each leaf composed of five to eleven leaflets. If you are unsure, check the tree identification key on the Trees Inside Out website.
The adult insect lays its eggs in cracks in the bark. Once hatched, the larvae burrow under the bark and bore into the cambium—the living part of the wood—as they eat. These long serpentine galleries eventually block the flow of sap, killing off the branches. The larvae of the emerald ash borer are identifiable by their bell-shaped abdominal segments. Between mid-May and late July, they emerge from D-shaped holes as adults.
Signs of infestation
- Notches nibbled in the leaves;
- D-shaped exit holes measuring 3.4–4 mm;
- S-shaped galleries under the bark.
The presence of the emerald ash borer can lead to the premature yellowing of the foliage and die-back in the crown of the tree. Stressed trees often produce shoots at their base, on their trunk or along their branches. Cracks measuring 5–15 cm may appear in the bark, over the galleries carved by the larvae. A healthy tree can quickly go into decline and die within three to four years. However, it is important to note that many other reasons may be causing sickness in an ash tree; other pests, cold and lack of water can lead to similar symptoms. Furthermore, many other species of insect can also make D-shaped holes. To formally identify a case of emerald ash borer infestation
What can you do?
- First of all, know how to distinguish ash from other deciduous trees.
- Learn to recognize the insect and the signs of its presence.
- If you detect signs of infestation, note the location of the tree and the symptoms observed.
- In Montréal, if it appears to be a municipal tree, contact your borough by calling 311.
- Contact the Canadian Food Inspection Agency at 1-888-463-6017 as soon as possible.
- If you catch an adult, keep it in a hermetically sealed container in the freezer.
- The Montréal Insectarium’s entomological information service can help you identify an insect specimen.
- Do not move firewood or wood residue.
- Cutting down infested trees is no longer systematically recommended, as transporting the felled wood risks spreading the problem. Instead, consult a Canadian Food Inspection Agency inspector, who will advise you on what measures to take.
Research is under way to develop biological control methods. Researchers have studied the impact of pathogenic fungus and parasitoid insects. So far, these studies have not produced conclusive results. Just one product has been approved by the Pest Management Regulatory Agency to combat the emerald ash borer: TreeAzin™, an insecticide derived from seed extracts of the neem tree, which is injected into the trunk. TreeAzin™ is expensive: $250–$1,000 per treatment, with each treatment lasting two years. Use of TreeAzin™ is restricted to arboriculture professionals. Before any treatment, it is essential to identify the pest responsible.
To learn more
- A Visual Guide to Detecting Guide Emerald Ash Borer Damage, Canadian Forest Service
- Emerald Ash Borer – Agrilus planipennis, Canadian Food Inspection Agency
Do you have questions about this blog?
Visit our Green Pages Or, go to the Horticultural information counter at the Botanical Garden for personalized service. One of our experts will be happy to give you more information.