How Montréal protects its ash trees

Montréal’s EAB control strategy aims to limit and delay ash tree mortality as much as possible. Thanks to our actions, many ash trees are still in good health. We are also quickly replacing felled ash trees to restore canopy (tree cover) losses.

In streets and landscaped areas

In our streets and the landscaped portions of parks, we treat healthy ash trees and cut down dying or dead ones.

So far, the treatments have conserved nearly 50,000 ash trees. 

We use an azadirachtin-based insecticide, a product with low environmental toxicity offering no danger to human health. The treatment is repeated every two years, in June through August. Green and blue dots applied to ash trees identify trees treated in even and odd years, respectively.

On local streets and in parks, mortality of treated ash trees is relatively low. We are now focusing our efforts in wooded areas, including large parks and nature parks.

In the woods

We’re using a different strategy. It’s about protecting the forest, not individual trees. 

Ash trees are transitional trees: they naturally give way to other tree species as the forest ages. 

When ash trees die, the available space is quickly filled by neighbouring trees or by the growth of young shoots (saplings) on the ground. The result of this “regeneration” process is that the canopy is never lost in these environments. When a large space is devoid of regeneration, we plant native trees and shrubs to help the canopy close.

We cut down dead ash trees along the edges of woodlands and on trails that cross them to ensure the safety of hikers. Other dead ash trees, nearer the centre, are not being felled. They will give way to the growth of neighbouring trees.

Diversifying tree species

We are diversifying the species of trees we plant on streets and in parks to make the urban forest more resilient to disease and pest attacks such as the emerald ash borer. Our vegetation palette includes 178 different species and varieties adapted to urban growing conditions.

Biological control of the emerald ash borer

Since 2015, Montréal has been working with the U.S. and Canadian governments to establish woodland populations of parasitoids: tiny wasps that attack the borer at specific stages. These natural enemies are safe for humans and pose a very low risk to native animal species.

This method has been used in recent years at the Jardin Botanique, the parc-nature Bois-de-Liesse and on the Westmount summit of Mont-Royal. The results show that the parasitoids establish themselves well in the area and disperse naturally. They represent a hope for future generations of ash trees in woodlands.

Fungus being tested against the EAB

Several experimental trials have been conducted in recent years with another biological control mechanism. Physically, it’s a funnel-shaped trap. Captured borers escape covered with spores of a fungus that will kill them a few days later. Before dying, each infected insect will have time to transmit the fungus to many others, which will eliminate them in turn.

Although the results are promising, the product is not yet licensed in Canada, nor is it marketed for widespread use.