Emerald Ash Borer

EAB infestation

The Emerald Ash Borer (EAB) is an invasive insect considered to be one of the worst forest pests to ever be introduced to North America. Since 2002, ash trees across large portions of the United States, Ontario and Quebec have been devastated by the EAB infestation. 

EAB lay their eggs in ash trees. The larvae eat the soft wood under the tree’s bark, preventing the tree from moving water and nutrients between its roots and leaves, and killing it within one to three years.

EAB only attacks true ash trees. In Oakville, green and white ash are the most common ash species, with blue and black ash being rare. Mountain ash and prickly ash have "ash" in their name but are not from the same species and are not susceptible to EAB.

Signs of EAB infestation to look out for:

• Leaves in the top third of the ash begin to die back
• New, thin branches begin to grow from the low trunk or roots
• White lines or canals under the bark
• Bark on the tree begins to split
• D-shaped exit holes in the bark formed by adult beetles exiting the tree
• Increased woodpecker activity on the tree

What you can do

If you have an ash tree, you have two options:

• Treat. If you have started a treatment program, great! Please continue treating. Continued treatment will help keep your tree healthy until after the infestation has died out. Treatment must take place between June and August. Due to the current infestation levels, if you have not yet begun a treatment program, it is likely too late to begin treatment to save your tree.
• Remove. Dead and dying trees can become structurally unsound. Remove and replace untreated ash trees with a different species. Doing nothing may put you and your property at risk. For information on removing private trees, visit our Private Tree Protection page.

What the town is doing

Oakville has one of the most aggressive management plans in Canada to combat EAB. Town Council approved a plan to treat a portion of the public ash canopy on streets and in parks with TreeAzin™, a biological insecticide.

Public ash trees receive treatment if they:

• Do not have cracks or holes in their trunk and if 60 per cent or more of their upper branches are healthy. TreeAzin™ is effective at protecting trees that meet these criteria. If a tree is unhealthy or has cracks or holes, treatment is unlikely to prevent it from dying from EAB infestation.
• Are at least 20 centimetres in diameter at the point on their trunk about 1.3 metres from the ground (diameter-at-breast-height or DBH). The town has determined that it is more cost-effective to remove and replace ash trees that are under 20 centimetres DBH than to treat them.

You may notice green dots and/or green ribbons on the trunks of public trees, indicating they are being treated.

Woodlands Hazard Abatement Program

The Woodlands Hazard Abatement Program is part of the town’s EAB management program to mitigate the impact of the invasive Emerald Ash Borer in woodlands. 

Starting in 2015 after a brief pilot program, and through 2019, the town removed hazardous dead and dying ash trees from the town’s trails and woodlands for public safety and to help the forest regrow. 

Due to the severity of the infestation most, if not all of the 43,000 ash trees in the town’s woodlands are now dead or dying. They are becoming brittle and structurally unsound due to the lack of nutrients caused by the EAB larva tunneling under the bark. Brittle trees can lose limbs or fall, causing serious injury to people using the trails, or serious damage to private property that borders the trails. 

Removing dead trees allows new trees and shrubs to grow, renewing the forest more quickly. 

While natural regeneration will account for most of the regrowth in the woodlands, the town will continue to establish concentrated planting sites to help the forest regrow more rapidly with desirable native species.

Canopy replacement

The town is replacing municipal street and park ash trees with trees of different species. Trees removed in the spring or summer will be replaced the following fall or spring. While natural regeneration will account for most of the regrowth in our woodlands, portions of select sites have been identified for enhanced and/or intensive regeneration and replanting.

Learn more about what the town is doing to replace ash trees on our Tree Planting page.