Emerald Ash Borer

Emerald ash borer (EAB) is a wood-boring beetle that kills ash trees. It was introduced to North America from Asia. The beetle is already having a devastating impact on Ontario, Quebec, and a number of states in the U.S. including Minnesota. Manitoba has been on high-alert for EAB for some time, however on November 30, 2017 EAB was officially confirmed in Winnipeg.

All ash species are susceptible in varying degrees. Trees as small as 1-inch in diameter can be attacked, meaning that trees can succumb to the pest even before they produce seed. The City of Winnipeg has completed its private ash inventory and it is estimated that ash trees make up about 40% of Winnipeg’s urban forest. EAB will have a significant negative impact on Manitoba’s native ash forests and on those planted in our towns and cities.

What to Look For

The immature form of EAB beetles (the cream-coloured, worm-like larvae) is responsible for most of the damage. The larvae feed just under the bark and create S-shaped tracks as they move throughout the trunk. These tracks disrupt the flow of water and nutrients up the tree, causing the tree to die. These S-tracks are only visible once the bark has been scraped away.

The larvae grow into adult beetles which chew their way to the bark surface and leave behind D-shaped exit holes. The adult beetle is shiny emerald or copper-green in colour. Its torpedo-shaped body is about 5-15 mm (1/2 inch) long.

Trees infested with EAB will show signs of general decline:

  • Dying branches near the top of the tree
  • Epicormic shoots (suckers) emerging from the trunk or from the base of the tree
  • Unusually heavy seed-crops
  • Trunk deformities such as cracks and splits.

These symptoms may not be obvious until the tree is heavily infested – but if you notice any of these signs, please contact 311 or Trees Winnipeg right away. 

Slow the Spread of Emerald Ash Borer

Don’t move firewood – burn it where you buy it!

EAB is largely spread through firewood and other wood products from EAB-infested areas. Now that EAB is in Winnipeg, we are urging Winnipeg residents to keep your firewood at home – if you’re going to the campground or cabin, buy firewood when you get there.


Report Suspicious Trees & Symptoms

If you see an ash tree displaying any of the symptoms above, please report it! Your vigilance can help prevent EAB from spreading. Contact 311 or Trees Winnipeg right away.

Join the Winnipeg Forest Watch Program

Become a Volunteer for our Winnipeg Forest Watch Program. The Forest Watch will be a volunteer based neighbourhood surveillance program that will help locate EAB in Ash select neighbourhoods across Winnipeg. To learn more about the  Winnipeg Forest Watch Program, click here.

Preventative Chemical Treatments

Injectable insecticides are available for those who want to try to protect high-value ash trees on their property. These treatments are most effective when applied to healthy trees and must be repeated every couple of years. These treatments should be done by a professional arborist. For tips on how to find an arborist, click here.

Caring for City-Owned Trees

If you wish to have boulevard or other city-owned ash trees treated or pruned at your own expense, you can apply for permission by filling out a property owner’s agreement and you can hire from a list of arborists recommended by the City of Winnipeg. For the agreement form and more information, click here. You can also volunteer for the our neighbourhood surveillance program. To learn more about the  Winnipeg Forest Watch Program, click here.

How to Identify an Ash

Green and black ash are native species to Manitoba, naturally found in riparian forests. Both species are also commonly planted in urban areas and ash currently accounts for over 30% of Winnipeg’s urban forest. Mancana ash (or Manchurian ash) is an ornamental ash from Asia, and has also become very common in our communities.

Leaf: Compound leaf – meaning there will be 5 to 9 leaflets on a single petiole arising out of a single bud. Each leaflet is serrated, oblong, and pointed.

Bud: Opposite bud arrangement – meaning that two buds will arise side by side on a twig (apart from the bud on the end of the twig). The terminal (end) bud will be flanked on either side by another bud.

Bark: Green Ash is distinguished by its thatched diamond shaped bark grooves. The grooves deepen as the tree matures. Black ash will have very smooth grey bark when young and then develop warty bark which feels corky when manipulated. Manchurian ash is a non-native species planted in Winnipeg and has smooth beige bark which develops very shallow linear grooves as the tree matures.

Form: Green ash and black ash usually have a  strong single leading stem can be seen stretching almost to the top of the tree. Green ash may also have codominant stems (two competing leading stems). Manchurian (also called Mancana) ash typically has a trunk that splits into many stems after a short way up and has a very round canopy (sometimes resembling a lollipop).

Compound leaf of green ash; and mature forms green ash (middle) and Mancana ash (right).