Tree Pests and Diseases

There are numerous tree pests and diseases in Wellington County. Information is provided a few of these that pose the biggest threat to tree/forest health and biodiversity. 

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Dying ash tree surrounded by healthy trees and reaching up towards a bright sky.

Don't Move Firewood - buy local, burn local.

The spread of invasive pests/diseases is commonly assisted by people unknowingly moving firewood with insects, insect eggs and/or fungal spores that are very difficult to see. Invasive tree pests and diseases pose a substantial risk to the environment and economy of Wellington County. A best practice is to burn firewood where you buy it. Be aware of the harms of moving firewood and movement restrictions that may be in place. 

Learn more about the Hazards of Moving Firewood


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An "Emerald Ash Borer" resting on a honeysuckle branch.

Emerald Ash Borer

A few years ago the Canadian Food Inspection Agency confirmed the presence of Emerald Ash Borer (EAB) in the Township of Puslinch. The infestation has continued to spread and intensify across our County. Experts have estimated that as many as 98% to 99% of the Ash trees will be killed over the next decade as a result. 

It is possible to protect trees with an inoculation. However, this is costly and must be repeated after a certain number of years. It is likely that this treatment will only be used on large specimens which have heritage values.

The most immediate problem is in our urban areas. Once dead, Ash trees become unstable quickly, creating a hazard. The trees will need to be removed, which will be costly over a number of years. Local municipalities will need to develop a plan to deal with the problem, and budget for this expense. Currently, there are no provincial or federal programmes to offset costs.

In our rural forests, up to 30% of the trees may be Ash in places. Their loss will have significant impact on our forest lands. Landowners are encouraged to manage the decline, marketing the trees while still of value. Replacement trees of the appropriate species should be replanted in the remaining forest. Wellington County's Green Legacy Programme will be able to assist replanting where needed with nursery stock in rural areas and larger potted stock in urban areas.


Spongy Moth (Lymantria dispar dispar)

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Adult gypsy moth on a leaf

The Lymantria dispar dispar (LDD) Moth, which is commonly referred to as the Spongy Moth or European Gypsy Moth, is a non-native insect that was introduced to Canada in 1969.

The impacts of defoliation from the LDD Moth can vary from minor to severe and it is generally understood that a healthy tree can withstand some defoliation. However, the defoliation of the trees can make them more vulnerable to disease, other insects, and environmental stressors. A single moth caterpillar can eat an average of one square meter of leaves.

The tree types most commonly impacted by the LDD Moth include oak, birch, poplar, willow, and maple trees. The Moth may also defoliate softwood trees such as white pine and blue spruce.

Frequently Asked Questions


Potential Tree Pests and Disease Threats

The following tree pests and diseases have not been found in Wellington County, but they have been confirmed in nearby municipalities or near the Ontario border. 

Asian longhorn beetle (Anoplophora glabripennis) sits on a green leaf.

Asian Long-Horned Beetle

Asian Long-horned Beetle (ALHB) is a large shiny black beetle with white dots on its back that can infest maple, birch, poplar, and willow trees. In 2013 an ALHB infestation was confirmed near Pearson International Airport.
Tree with bark falling off and an black dot of fungus in the centre of it.

Oak Wilt

An invasive vascular disease caused by the fungus Bretziella fagacearum threatening oak trees in Canada. The fungus grows on the outer sap wood of oak trees, restricting the flow of water and nutrients and can kill a tree within a single growing season.
Hemlock woolly adelgid (HWA) infestation on underside of eastern hemlock branch.

Hemlock Woolly Adelgid

A tiny, invasive aphid like insect that attaches to the branch and feeds at the base of needles extracting nutrients and sap. Once attacked by HWA hemlock trees do not recover and trees usually die within 4 to 15 years of infestation.

Not sure what type of trees you have?

Check out Forests Ontario to find out.