Hemlock Woolly Adelgid

What is Hemlock Woolly Adelgid?

Hemlock Woolly Adelgid (HWA) is an invasive insect native to eastern Asia that sucks sap from eastern hemlock tree branches and can kill a tree in 4 to 10 years if not treated.

HWA can be identified by its white, cottony ovisacs on the undersides of hemlock branches, near the base of the needles. The ovisacs may appear alone or in clusters. Late fall through early spring is the best time to check hemlock trees for the presence of HWA.

Eastern hemlocks are a unique keystone species of Michigan’s forests. They often occur on steep dunes or along rivers. They prevent soil erosion, provide critical shelter for animals like whitetail deer, porcupines, and songbirds, and shade and cool coldwater trout streams. Losing hemlocks to HWA would drastically alter the environment that wildlife depend on. By treating hemlocks for HWA, we slow the spread of this insect in our community and ensure we don't lose the valuable benefits of hemlock.

Mason-Lake Conservation District's HWA crew is grant-funded to look for and treat HWA on private property in Mason and Manistee counties and provide guidance to landowners on how to best manage HWA on their properties. See below to sign up or contact us for more information at the number at the bottom of the page.

Why is it important?

Trees on the right are healthy and lush after an HWA infestation was treated 4 years prior with systemic pesticides.

Photo: Effects of HWA in Muskegon County, MI

Where is HWA Currently Located?

HWA was first detected in Ottawa County, MI in 2015 and has moved north since then. It was first detected in Mason County in 2020. It is known to spread within 10 miles of the lakeshore. A tiny insect, it can be spread by wind, birds, or human, vehicle, or animal movement, especially from April - July when crawlers are mobile.

Taking Action Against Hemlock Wooly Adelgid (HWA)

Concerned about your hemlocks and want to protect them from HWA?
The process is simple—sign up, opt in, and we’ll handle the treatment.

Sign Up for our Free Detection Survey

A free detection survey is the first step to protecting your hemlock trees from the devastating impacts of HWA. During this site visit, our experienced team will examine your hemlock trees for signs of infestation. These surveys are conducted from late fall through early spring. If HWA is found on your property, our team can provide guidance on next steps, including treatment options, which may be available at no cost through grant funding.

To schedule a free survey, simply fill out and return our permission form and we will add you to our work list. Your presence is not required but you are always welcome to walk along with us.

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I have HWA on my property - What now?

If HWA is found on your property our team can provide guidance on next steps. Opt-in treatment may be available to you at no cost through our grant funding. If grant funding is not an option, we also provide further guidance to landowners interested in treating their own trees or hiring a private arborist.

Our team treats hemlocks with a systemic pesticide, imidacloprid, that is either injected into large trees or sprayed onto the trunk of smaller trees. These methods limit the pesticide to the direct vicinity of the tree and minimize impacts on the environment. It is the same chemical used in dog flea and tick medications. This treatment eliminates current infestations and protects the tree from reinfestation for 4-7 years.

What Can You Do As A Landowner?

Look at undersides of branches in December through March for small, white ovisacs. If found, note the location of the tree and, if possible, take photos of the infested branch. Report the finding to your local conservation district or at one of the reporting websites below. To avoid spreading HWA, do not collect sample branches or twigs.
from areas where hemlock trees are present, or move them at least 100 feet from hemlocks. Birds may carry these insects to a birdfeeder where they can be picked up and transported by other birds.
If you are in areas with hemlock trees, just brushing against an infested tree could bring these insects along for the ride! Run clothing through a dryer and wash or brush off gear and vehicles before moving to a new area. This is especially important from April-July when HWA crawlers are mobile.
Consider pruning low-hanging hemlock branches especially along roadways or driveways. Anecdotal evidence suggests this could help prevent infestation spread along high traffic areas.
Don't move hemlock brush or downed material off your property. The best option is to burn on-site. Transport to a disposal site with no hemlocks within 100 yards is allowed, if tightly covered when transported from March-October. Michigan currently is under a quarantine through the Michigan Department of Ag and Rural Development that restricts the movement of hemlock material in counties with HWA. See below links for more information.