Plan Spring Treatment for Hemlock Woolly Adelgid Now

If the hemlocks on your property are showing signs of hemlock woolly adelgid infestation, now is a good time to plan spring treatment for this invasive species.

The hemlock woolly aphid, native to Asia, is found in areas of Allegan, Mason, Muskegon, Oceana, and Ottawa counties in Michigan. These small insects suck sap from hemlock needles and can ultimately kill trees.

“Insecticides are available to control the insect, and in many cases landowners can easily apply them by carefully following label directions and application rate guidelines,” a statement read. press release from the Michigan Department of Natural Resources. “In Michigan, the label is law. Due to certain restrictions on the use of these insecticides, you may require the services of a licensed pesticide applicator.”

If one or more trees are infested, plan to take action this year. Without treatment, trees infected with the hemlock woolly adelgid may die within four to ten years. Weakened trees in a residential landscape could spell disaster during high winds or storms, and they will eventually need to be removed. Loss of hemlocks in forested areas can reduce shade, winter cover, food, and habitat for birds, fish, and mammals.

Products containing imidacloprid or dinotefuran as the active ingredient and labeled for the treatment of hemlock woolly aphid are effective in controlling 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 five years.

Dinotefuran moves faster through hemlocks, making it ideal for heavily infested trees. Dinotefuran protects trees for one to two years.

Treatment plans should include all hemlocks on his property over the next few years. If the hemlock woolly adelgid is present, symptomless hemlocks are very likely to become infested over time. It’s a good idea to discuss treatment plans with neighbors and coordinate efforts when possible.

Can I treat the trees myself?

Applying imidacloprid or dinotefuran is simple enough that many landowners can do it themselves. Products containing these chemicals are available at garden supply stores, packaged under various trade names in either liquid or granular form.

Imidacloprid and dinotefuran products available from garden stores are usually applied to the soil near the trunk of the tree, where they are taken up by the root system. Schedule application between early April and late October, when the ground has thawed and soil moisture is moderate, not too dry or saturated. The treatment is more effective the earlier it is applied.

MNR recommends that those treating their trees follow all label directions, wear proper safety equipment, and determine the correct rate of application to ensure positive results. To protect the environment, do not allow pesticide to enter or enter storm sewers, drainage ditches, gutters or surface waters.

More information about do-it-yourself treatment can be found in the MSU Extension Bulletin: Guidelines for Owner Treatment of Hemlocks Infested with Hemlock Woolly Adelgidavailable at michigan.gov/HWA.

When should I call a professional?

Licensed pesticide applicators have a wider range of options for applying treatments than consumers, and their professional skills are recommended in some situations.

One county by county list of companies holding a pesticide application licenses can be found on the Michigan Department of Agriculture and Rural Development website, michigan.gov/MDARD. For lawn or landscaping trees, look for a licensed professional under the “ornamental” category; for forest trees, choose the “forestry” category.

If the hemlocks are within 75 feet of a body of water or in areas with high water tables, or if flowering plants or shrubs grow around the hemlocks that need protection, trunk injection or a 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 the treatment?

The cottony, white eggs of the hemlock woolly adelgid will persist for some time after treatment. If trees are treated in the spring with dinotefuran, check new growth in late fall or winter for any new signs of infestation. With imidacloprid, wait one year after treatment to assess effectiveness.

After treatment, the trees should be checked annually. If the insect has returned after using dinotefuran, reapplication may be required after one to two years. For imidacloprid, consider retreatment every five to seven years.

Do my trees have the hemlock woolly aphid?

It is important for those who have hemlocks on their property to check them for signs of hemlock woolly adelgid, which only infests hemlocks. Those unable to identify if their trees are hemlocks are encouraged to use the Michigan Invasive Species Program’s eastern hemlock identification guide.

The round, white, cottony ovisacs of the aphid are most noticeable in winter and are located on the undersides of hemlock branches at the base of the needles. The publication Hemlock woolly adelgid lookalikesavailable at michigan.gov/HWAprovides pictures and information on identifying this pest and other pests commonly confused with it.

How do I report an infestation?

Those who believe that trees on their property have the hemlock woolly adelgid are asked to report it using the Midwest Invasive Species Information Network at MISIN.MSU.edu. Reports can also be made in the field using the MISIN smartphone app, which will log the location and allow you to upload photos of suspicious signs of the insect.

People can also take photos, note the location of the tree, and email the information to the Michigan Department of Agriculture and Rural Development at [email protected] or report by calling 800- 292-3939.

The DNR asks people not to cut samples of infested branches and transport or mail them. This could accidentally spread the insect to new areas. A inland quarantine of the state makes it illegal to move hemlock anywhere inside or outside of Allegan, Ottawa, Muskegon, Oceana or Mason counties. Currently, there are no known hemlock woolly adelgids in Benzie County, as a detection of a single tree has been destroyed. Hemlock waste in quarantined counties may be moved to approved disposal sites within the quarantine area.

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

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