Invasive Species Watch: Hemlock Wooly Adelgid

by | Jan 18, 2024 | Invasive Species, News

Eastern hemlock trees are some of the largest and most common trees in Northern Michigan and the northeastern states. They play an ecologically vital role in our environment as well as providing habitat for many species. Unfortunately, these beautiful trees are under attack from a non-native insect called the hemlock woolly adelgid (Adelges tsugae). Without successful intervention, this invasive pest could kill many hemlocks here in Michigan and nationwide.

Since its arrival in the United States in the 1920s, the hemlock woolly adelgid has rapidly colonized parts of the Northeast and the Mid-Atlantic States, where it feeds on the eastern hemlock. Spread by birds, wildlife, wind, and human activity, it is recognizable by small, white, cottony masses on the underside of branches especially from November to July. It makes trees appear grayish-green and unhealthy. Eastern hemlocks are distinguished by flat green needles with white stripes underneath.

If you notice these signs on hemlock trees, report the infestation to Michigan’s Department of Agriculture, via the MISIN online tool or the smartphone app. Reporting infestations is essential for tracking the pest’s reach and informing necessary surveys.

Treatment generally requires specific insecticides. It is recommended to consult a qualified arborist. Michigan enforces quarantines to limit this pest’s spread. For those handling treatment themselves, follow the MSU Extension’s guidelines, available in the article, “How to treat hemlock trees for hemlock woolly adelgid.” 

For detailed information on identification, reporting, or treatment, visit Michigan’s Invasive Species Program’s hemlock woolly adelgid page at Michigan.gov/HWA.