Hemlock woolly adelgid

Rouge National Urban Park

Parks Canada has confirmed the presence of hemlock woolly adelgid in Rouge National Urban Park. Hemlock woolly adelgid is an invasive, aphid-like insect that attacks and kills hemlock trees by feeding on sap at the base of needles. This feeding causes needle loss, branch dieback and eventually tree death.

The detection of hemlock woolly adelgid near the Mast Trail area marks the first known occurrence of hemlock woolly adelgid within the park, confirmed by the Canadian Food Inspection Agency (CFIA).

About hemlock woolly adelgid

Hemlock woolly adelgid
Photo : David Gillis

Hemlock woolly adelgid (Adelges tsugae) is a tiny insect — less than 1.5 millimetres long — with a distinctive white, woolly covering that can be seen on the undersides of twigs at the base of needles. It spreads naturally through wind, birds and other animals, but human activity (such as transporting infested nursery stock, firewood, or other wood products) can greatly accelerate its spread. Once established, hemlock woolly adelgid feeds on the tree’s stored nutrients, slowly starving the tree. Infested hemlocks can die within 4 to 15 years, depending on the severity of the infestation and environmental conditions.
 

The importance of hemlocks

Hemlock trees are a vital part of forest ecosystems at the Rouge. They provide shade that regulates stream temperatures for fish and other aquatic life, offer important habitat for birds, mammals, and insects and help prevent soil erosion along slopes and waterways. The loss of hemlocks can cause major changes to forest structure, wildlife habitat and water quality.

Hemlock trees near Little Rouge Creek, Rouge National Urban Park 

Next steps

Parks Canada is working closely with the CFIA, the Ontario Ministry of Natural Resources and Forestry and the City of Toronto to monitor and respond to the detection of hemlock woolly adelgid. Field staff are conducting surveillance to determine the extent of the infestation in and around the park, mapping affected areas and evaluating options to slow the spread. Where possible, healthy hemlocks may be protected through targeted treatments or other management techniques as part of a long-term strategy to preserve this important tree species.

How the public can help

To limit the spread, visitors should:

  • stay on designated trails
  • respect closures and follow all posted restrictions and biosecurity guidelines
  • avoid brushing against or touching hemlock trees, or moving downed woody debris from hemlock trees
  • keep pets on a leash and out of infested areas
  • clean boots, clothing, and gear after visiting hemlock forests, or when moving from one forest to another
  • refrain from moving wood and plant materials in the park
  • add observations to the iNaturalist invasive species project 
  • report infected plants or suspected pests to the CFIA at: Stop the spread and help keep invasive species out of Canada

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    Related links

    Canadian Food Inspection Agency – Hemlock Woolly Adelgid

    Invasive Species Centre – Hemlock Woolly Adelgid

    CleanPlayGo

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