How you can help protect your hemlock trees from invasive hemlock woolly adelgid

Invasive pest confirmed in 5 southwest Michigan counties

Round, white hemlock woolly adelgid ovisacs are found on the undersides of branches near the base of the needles. (Michigan Department of Natural Resources)

The Michigan Department of Natural Resources is asking people with eastern hemlock trees on their property to take time this winter and check them for signs of hemlock woolly adelgid.

Winter is the best time to look for evidence of an infestation. As the tiny, soft-bodied insects feed, they consume a hemlock’s stored nutrients and slowly suck the life from the tree.

“Cooler temperatures trigger feeding activity,” Robert Miller, MDARD’s invasive species prevention and response specialist 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.”

The insects are not native to Michigan and can cause significant harm to Michigan’s hemlock trees. There are an estimated 170 million hemlock trees in the state. Infestations of hemlock woolly adelgid have been confirmed in Allegan, Ottawa, Muskegon, Oceana and Mason counties.

Read: Meet Michigan’s 8 invasive insects: What they are, the damage they cause and what to do about them

What you can do to help

During the winter, survey crews from several invasive species management areas will look for signs of infestation. They will be conducting surveys within a 5-mile border along the Lake Michigan shoreline.

Hemlock trees can be protected with insecticide treatments. During the survey, infested trees and any other hemlocks within the area will be mapped and tagged for summer treatment.

If you have hemlocks on your property, you should take some time to check for signs of infestation. 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.

How to identify a hemlock tree

Hemlock trees have small, papery cones and short needles that are dark green on top. (Michigan Department of Natural Resources)

The adelgids feed and form ovisacs only on eastern hemlock trees in Michigan, which is why it’s important to distinguish them from other conifers like pines or spruces.

The DNR suggests looking for the following:

  • Cone- or egg-shaped trees up to 75 feet tall.
  • Drooping or feathery branches.
  • Flat needles growing individually from the sides of twigs.
  • Needles that are dark green on top with two parallel, white stripes underneath.
  • Papery cones about three-quarters of an inch long that hang downward from branches.

You should look on the undersides of branches for evidence of round, white ovisacs near the base of the needles. Up close, ovisacs look like tiny cotton balls and may appear alone or in clusters.

How to report infested hemlock trees

If you find an infested hemlock tree, you can report it by using the Midwest Invasive Species Information Network online by clicking here.

Reports also can be made by email to or by phone to MDARD’s Customer Service Center at 800-292-3939.

Share the location of the infested trees and try to take one or two pictures of infested branches to help confirm identification. To not collect sample branches or twigs.

How hemlock trees can be treated

There are certain insecticides that can successfully treat the infestation if used correctly.

Without treatment, infested trees can die within four to 10 years. A qualified arborist can diagnose and assist with treating infested trees.

If you are able to handle treatment on your own, the DNR recommends following guidance from the MSU Extension bulletin here.

Even if you plan to handle treatment on your own, you should still report the infestation so officials can track where hemlock woolly adelgid has spread.

A certified pesticide applicator prepares to inject an infested hemlock tree with pesticide. (Michigan Department of Natural Resources)

About the Author:

Kayla is a Web Producer for ClickOnDetroit. Before she joined the team in 2018 she worked at WILX in Lansing as a digital producer.