Invasive hemlock woolly adelgid infestation identified in Leelanau County

Hemlock Woolly Adelgid | State of Michigan photo

Leelanau County has been added to Michigan’s hemlock wooly adelgid quarantine, after the insect was found on trees on a private property in Leelanau Township, becoming the ninth county in the state with an active infestation.

Hemlock woolly adelgids are small insects that extract sap from hemlock trees. This can cause needles and buds to die, thinning canopies, slowing tree growth as they take on a grayish-green appearance. Without treatment, these trees die within four to 10 years.

Allegan, Antrim, Benzie, Mason, Muskegon, Oceana, Ottawa, and Washtenaw counties are also facing infestations.

“Hemlock woolly adelgid likely arrived in Michigan on infested nursery stock from northeastern or mid-Atlantic states. Although the tiny insects don’t move far on their own, they can be blown by wind or hitchhike on birds or animals. In a similar way, cars, boats, or RVs parked under infested trees may be able to transport the insects to new locations,” Molly Mott, Michigan Department of Agriculture and Rural Development (MDARD) plant health section manager said in a statement.

Mott advised those headed outdoors to park in designated areas, clean their gear and vehicles before traveling and to leave firewood at home to avoid spreading an infestation.

Infested trees can be identified by looking at the underside of hemlock shoot branches for evidence of cotton ball-like ovisacs at the base of needles. These ovisacs can appear alone or in clusters.

MDARD advises residents to review photos and descriptions of hemlock woolly adelgid lookalikes at Michigan.gov/HWA before reporting a suspected infestation. The website also includes information for identifying hemlock trees, as well as the invasive species.

Suspected infestations can be reported by emailing MDA-Info@michigan.gov or by by calling 800-292-3939. Reports can also be made with the Midwest Invasive Species Information Network (MISIN) online reporting tool , or with the MISIN app.

While making a report, MDARD advises people to be prepared to share the location of the infested tree, and share one or two photos of the infested branches to help confirm the identification. It advises against collecting simple branches or twigs to avoid spreading the infestation.

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