Plan now for spring treatment of hemlock woolly adelgid

If hemlock trees on your property show signs of hemlock woolly adelgid infestation, now is a good time to plan for spring treatment of this invasive species. Hemlock woolly adelgid, native to Asia, is known to be present in areas of Allegan, Antrim, Benzie, Leelanau, Manistee, Mason, Muskegon, Oceana, Ottawa, Van Buren and Washtenaw counties in Michigan. These small insects suck sap from hemlock needles and ultimately can cause tree death.

Insecticides are available to control the insect, and in many cases, landowners can apply them easily by carefully following label instructions and application rate guidance. In Michigan, the label is the law. Due to certain restrictions on the use of these insecticides, you may need the services of a licensed pesticide application business. If one or more trees are infested, make plans to act this year. Without treatment, trees infested with hemlock woolly adelgid are likely to die within four to 10 years. Weakened trees on a home landscape could spell disaster during high winds or storms, and eventually they will have to be removed. Loss of hemlocks in forested areas can reduce shade, winter cover, and food and habitat for birds, fish and mammals.

Which treatments work?

Products containing either imidacloprid or dinotefuran as the active ingredient and labeled for treatment of hemlock woolly adelgid are effective in combatting the insect.

• Imidacloprid moves slowly through trees, taking at least a year to reach the top of a large tree. However, one application will protect the tree for at least four years.
• Dinotefuran moves through hemlock trees more quickly, making it ideal for heavily infested trees. Dinotefuran protects trees for one to two years.

No matter which treatment you select, be sure your treatment plan includes all hemlocks on your property over the next few years. If hemlock woolly adelgid is on your site, hemlocks without symptoms are very likely to be infested over time, including trees on neighboring properties. It’s a good idea to discuss treatment plans with neighbors and coordinate efforts when possible.

Can I treat trees myself?

Application of imidacloprid or dinotefuran is simple enough for many landowners to do themselves. Products containing these chemicals are available at garden supply stores, packaged under various trade names in liquid or granular form. Check the label or ask for assistance in selecting the right product.

Imidacloprid and dinotefuran products available at garden supply stores generally are applied to the soil close to the tree trunk, where they are absorbed through the root system. Plan your application for a time between early April and late October, when the ground has thawed and soil moisture is moderate – not too dry or saturated. The sooner you treat, the more successful your treatment will be.

Follow all label directions, wear appropriate safety gear and determine the right application rate to ensure positive results. To protect the environment, do not allow the product to enter or run off into storm drains, drainage ditches, gutters or surface waters.

Some products have restrictions on the amount that can be applied to an area per year. Be sure to read the label carefully to determine if the amount you need falls within these limits. If not, you may need to adopt a multiyear plan or hire a professional.

More information on do-it-yourself treatment can be found in the Michigan State University Extension bulletin Guidelines for homeowner treatments of hemlock trees infested with hemlock woolly adelgid.

When should I call a professional?

Licensed pesticide application businesses have a broader range of options for applying treatments than consumers, and their professional skills are recommended in certain situations. A county-by-county list of businesses holding pesticide application licenses can be found on the Michigan Department of Agriculture and Rural Development’s website, Michigan.gov/MDARD. For lawn or landscape trees, look for a professional licensed in the ornamental category (3B); for forest trees, choose the forestry category (2). If your hemlock trees are within 75 feet of a body of water or in areas with a high water table, or if flowering plants or shrubs are growing around the hemlocks you wish to protect, a trunk injection or bark treatment may be necessary to avoid affecting the environment, groundwater or other insects. Professional applicators can provide these types of treatments.

What should I expect after treatment?

Hemlock woolly adelgid’s cottony, white ovisacs will linger for a time following treatment. If trees are treated in the spring with dinotefuran, check new growth in late fall or winter for any fresh signs of infestation. With imidacloprid, wait until a year after treatment to gauge effectiveness.

After treatment, trees should be checked every year. If the insect has returned after dinotefuran was used, reapplication may be needed after one to two years. For imidacloprid, consider retreatment every four to seven years.

Do my trees have hemlock woolly adelgid?

If you have hemlock trees on your property, it is important to check them for signs of hemlock woolly adelgid, which infests only hemlock trees. If you are not sure whether your trees are hemlocks, use the Michigan Invasive Species Program’s eastern hemlock identification guide.

The adelgid’s round, white, cottony ovisacs are most visible in the winter and are located on the undersides of hemlock branches at the base of the needles. The publication Hemlock Woolly Adelgid Look-Alikes provides images and information on identifying this and other pests commonly mistaken for it.

How do I report an infestation?

If you suspect trees on your property have hemlock woolly adelgid, report it using the Midwest Invasive Species Information Network at MISIN.MSU.edu. You can report from the field using the MISIN smartphone app, which will log the location and allow you to upload photos of the suspected signs of the insect.

You also can take pictures, note the tree’s location and email the information to MDARD at [email protected] or report by calling 800-292-3939. Someone will respond to let you know if hemlock woolly adelgid is present or not.

Please do not clip infested branch samples and transport or mail them. This could accidentally spread the insect to new areas.

For more information on identifying and managing hemlock woolly adelgid, visit Michigan.gov/HWA.

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

Note to editors: Accompanying photos are available below for download. Caption information follows.

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

HWA treatment: Certified pesticide applicators inject an infested hemlock tree with pesticide.

Contact: Kerry Heckman, 517-643-1256

Ensure the future of your forest through the Forest Legacy Program; nominations due May 2

How do you protect your forest for future generations? Michigan’s Forest Legacy Program offers some options. It provides the state with funding to purchase or secure conservation easements on environmentally important forest lands to ensure that our next generations can enjoy them as well. The Forest Legacy Program is a partnership between the U.S. Department of Agriculture’s Forest Service and the Michigan Department of Natural Resources. “The Forest Legacy Program protects forest lands so they will provide the benefits of forests forever,” said Kerry Heckman, forest land administrator with the DNR’s Forest Resources Division. “Well-managed forests are a critical source of the forest products we use every day. Forests help provide us with clean air and water and are the places we love to hunt, hike, fish and connect with nature.” Do you have a parcel that could benefit from Forest Legacy Program protection? Nomination applications for the nationally competitive program are due May 2. Past examples of forest lands secured by the program are parcels along the Lake Superior shoreline and in the Pigeon River Country State Forest. More than 156,000 acres have been protected in Michigan. These forests were competitive for program funding because they: Are managed as working forests to keep them healthy and thriving. Contain prime fish and wildlife habitat. Offer outdoor places to enjoy. Benefit the forest products economy.

Protected forests will always be forests

The Forest Legacy Program provides an opportunity for landowners to keep forests as forests, encourages sustainable management and supports forest product markets.

All interests in land acquired by the Forest Legacy Program last forever. Agreements must contain language ensuring that rights are perpetual. Michigan’s program requires that Forest Legacy lands are open to the public, at a minimum, for nonmotorized access. Landowners who don’t have an existing forest management plan will need to develop one before a project can be completed.

The DNR will review and prioritize eligible projects and may submit up to three to compete nationally for funding. Projects nominated by May 2 will compete for funding in the fiscal year 2027 federal budget, which begins Oct. 1, 2026. The state can request up to $20 million for projects.

Nominate your forest land

Find details and download a nomination application on the Forest Legacy Program webpage. Email program lead Kerry Heckman at [email protected] for more information.

Note to editors: An accompanying photo is available below for download. Caption information follows.

Black River Ranch forest: Aerial view of the Black River Ranch forest, a Forest Legacy Program-enrolled property bordering the Pigeon River Country State Forest in Michigan’s northern Lower Peninsula.