Invasive Plants and Insects

Emerald Ash Borer (EAB)

Emerald Ash Borer is an invasive insect from Asia that attacks and kills untreated Ash trees. The town has a strategy to detect and manage EAB in Oakville. For more information about EAB, what the town is doing and how you can help, visit the Emerald Ash Borer page.


The town is experiencing a higher than normal volume of aphids this year, particularly on linden trees. Aphids are native, small, soft-bodied insects that feed on plants and trees by sucking sap from leaves and stems. Populations are at their peak during the late summer, and are expected to decline with cooler weather in the fall. Most trees are able to tolerate high populations of aphids and residents should not be concerned about the risk to their trees. Using a hard jet of water from a hose or an insecticidal soap spray (which is exempt from the town’s pesticide ban) can reduce their populations. Avoid using broad-spectrum insecticides as they also kill ladybugs and other beneficial insects that feed on aphids. Additional information is available from Health Canada.


The town is experiencing a population increase of Cankerworm this spring 2017. Cankerworm is a native insect found through the majority of Canada. There are two types of Cankerworm: Spring and Fall. Cankerworm undergoes natural population increases every 10-15 years that last for one or two years. They feed on tree leaves from May through mid-June and then go underground to reemerge in the fall as moths.

After the initial feeding by cankerworm, trees will often have a second flush of new leaves. Although cankerworm can be an additional stress for trees to undergo, it is generally not the primary cause of mortality. Healthy trees will usually survive a moderate single year defoliation. Population increases in native pests such as cankerworm play a crucial role as a food supply for many of the native species of birds that live in Oakville’s urban forest.

The Town of Oakville is currently tracking areas where there is a population outbreak of cankerworm to include in a management program for 2018. However, it is expected there will be a natural decline of cankerworm after this outbreak from natural prey and disease.

Visit EOMF - Cankerworm to learn more.

Lyme disease and ticks

Based on the Region’s surveillance of tick submissions and human cases, the risk of acquiring Lyme disease in Halton is very low. Learn more about Lyme Disease.

Asian Long-Horned Beetle (ALHB)

ALHB has not been detected in Oakville.

On September 20, 2013, the Canadian Food Inspection Agency (CFIA) confirmed the presence of (ALHB) in an industrial area near Pearson International Airport in Mississauga, Ontario. Review the full news release.

ALHB is not native to Canada and was first detected in the cities of Vaughan and Toronto in 2003. The CFIA announced on April 5, 2013, that ALHB has successfully been eradicated from that area.

The damage it can cause extends to many broadleaf trees, such as maple, birch, elm, poplar and willow. For more information on ALHB, please visit YouTube.

ALHB may be confused with some native insects. Please compare the photos on the CFIA website when trying to identify ALHB. If you think you have seen the beetle or signs of its damage within Oakville, please take a picture if you can and report your findings to the CFIA at 1-800-442-2342.

Gypsy Moth

The Gypsy Moth, an invasive pest from Europe and Asia, is a concern because the caterpillar (larvae) feed voraciously; mostly on the leaves of oak and other deciduous trees. Visit the Health Canada website to learn more about effective control of Gypsy Moth.


Buckthorn thrives in a variety of habitats and forms dense thickets that crowd and shade out native plants. It produces large numbers of seeds that germinate quickly and can alter nitrogen levels in the soil, creating better conditions for its own growth and discouraging the growth of native wildflowers, shrubs and trees.

Garlic Mustard

One of the greatest threats to woodlands in Oakville and across Ontario is Garlic Mustard (Alliaria petiolata), an invasive plant that displaces native wild flowers and plants, including White Trilliums. The Town of Oakville partners with local community groups to organize Garlic Mustard pulls.

Giant Hogweed and Wild Parsnip

Giant Hogweed is a large, invasive plant whose sap contains chemicals that can cause skin to become hypersensitive to sunlight and erupt in painful blisters. Similar to Giant Hogweed, the sap of Wild Parsnip plants can also cause skin irritations, burns, or blisters. For more information on how to identify Giant Hogweed and Wild Parsnip, visit the Giant Hogweed and Wild Parsnip page.