Time To Check Trees For Hemlock Woolly Adelgids

Press release from Michigan DNR:

Dec. 13, 2021

Contact: Rob Miller, 517-614-0454 Media contact: Joanne Foreman, 517-284-5814 Agency: Natural Resources

Dec. 13, 2021

Invasive pest already confirmed in five southwest Michigan counties

Hemlock woolly adelgids, tiny invasive insects that suck nutrients from hemlock trees, are known to be present in Allegan, Ottawa, Muskegon, Oceana and Mason counties.

State agency staff, university researchers and regional cooperative invasive species management areas have been working to identify and contain infestations that span across public and private lands.

Can't see the table below? Click here to view the original story.

Winter is the optimum time to look for evidence of an infestation, according to Robert Miller, MDARD's invasive species prevention and response specialist.

"Cooler temperatures trigger feeding activity," Miller said. "As hemlock woolly adelgids feed, they secrete a white, waxy material that creates ovisacs. The presence of these small, round, white masses makes it possible to identify infested trees."

These insects are considered invasive because they are not native to the state and cause significant harm to Michigan's hemlock resource. With no pressure from native predators or diseases, HWA populations continue to grow, threatening an estimated 170 million hemlocks across the state.

Winter surveys underway

Can't see the table below? Click here to view the original story.

Your help is needed

Though crew members will cover a lot of ground, they won't be able to check all trees. If you have eastern hemlocks on your property, take some time to look for signs of hemlock woolly adelgid. Anyone spending time outdoors is encouraged to do the same.

In Michigan's northern forests, hemlock trees are found in moist soils along streams and riverbanks and along coastal dunes. Hemlock also is popular as a landscape tree in parks and residential areas.

Identify hemlock trees

Can't see the table below? Click here to view the original story.

Look for signs

Late fall through early spring is the best time to check hemlock trees. Look on the undersides of branches for evidence of round, white ovisacs near the base of the needles.

Up close, ovisacs look like balls of spun cotton and may appear alone or in clusters. The short video "Hemlock woolly adelgid: Invasive species in Michigan" provides helpful identification tips.

Report your findings

Can't see the table below? Click here to view the original story.

Manage your trees

If you find hemlock woolly adelgids on your property, it is important to know that certain insecticides are successful in treating the infestation if used correctly. A qualified arborist, such as one certified by the International Society of Arboriculture, can diagnose and assist with treating infested trees. Additional help is available through local cooperative invasive species management areas.

If you are able to handle treatment on your own, follow the guidance provided in the MSU Extension Bulletin: "How to treat hemlock trees for hemlock woolly adelgid."

Reporting infested trees, even if you will be managing them on your own, is important to help determine how far hemlock woolly adelgid has spread. This information also indicates where additional surveys may be needed.

For more information on identification, reporting or treatment, visit the Michigan Invasive Species Program's hemlock woolly adelgid page at Michigan.gov/HWA or contact Drew Rayner, DNR West Michigan hemlock woolly adelgid coordinator, at RaynerD1@Michigan.gov or 517-231-8763.

Michigan's Invasive Species Program is cooperatively implemented by the Department of Environment, Great Lakes, and Energy, the Department of Natural Resources, and the Department of Agriculture and Rural Development.

/Note to editors: Accompanying photos are available below for download. Suggested captions and photo credit information follow:

Ovisac: In the winter, hemlock woolly adelgids secrete white, waxy material to protect their eggs. Photo courtesy of Lorraine Graney, Bartlett Tree Experts, Bugwood.org

Snow: A CISMA survey crew checks for hemlock woolly adelgid in a snowy forest. Photo courtesy of West Michigan CISMA.

Hemlock twig: Hemlock trees have small, papery cones and short needles that are dark green on top.

Infested branch: Round, white hemlock woolly adelgid ovisacs are found on the undersides of branches near the base of the needles./

This press release was produced by the Michigan DNR. The views expressed here are the author’s own.