Hemlock Woolly Adelgid: Near, But Not Yet Here

Hemlock woolly adelgid

Manage this Invasive Species

This is part one of a three-part serieson invasive species — updates in the ever-changing world of invasive species management.

Landowners with hemlock trees should be on alert as a new invasive insect is killing trees in Ontario.

For such a tiny insect, the hemlock wooly adelgid (HWA) can cause quite large problems. These aphid-like insects are native to Asia but were introduced to North America on infected nursery stock in the early 1900s. Since then, they’ve spread across the eastern United States and into some parts of Canada.

Like their name suggests, HWA feeds on eastern hemlock (Tsuga canadensis) trees. Look out for white, wool-like masses gathered along the underside of eastern hemlocks branches near the base of the needles. These are the signs of an infestation which will cause a tree to die within 4 to 15 years.

Eastern hemlock trees are a keystone species in our watershed. They provide valuable habitat and food for wildlife, their dense canopies help keep the ground and waters cool below, and their roots add stability to streambanks.

CVC’s Invasive Species Management Program has been monitoring for HWA on high priority CVC properties since 2016. This effort has been expanded in 2023 to include more properties with hemlock stands. To date, no HWA has been found in our watershed, but there have been two recent discoveries in Ontario, in Grafton (2022) and Hamilton (2023).

Landowners can check lower hemlock branches and those that have fallen to the forest floor for signs of the woolly masses or the very small HWA nymphs/adults.

Early detection of this species is critical. If you suspect HWA, report it immediately to the CFIACVC or EDDMapS.

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