Department of Natural Resources
March 23, 2021
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 (pronounced -ə-ˈdel-jəd ), native to Asia, has been detected in Allegan, Ottawa, Muskegon Oceana, Mason and Benzie counties in Michigan. These small insects suck sap from hemlock twigs and ultimately can cause tree death.
|Insecticides are available to control the insect, and in many cases, landowners easily can apply them by carefully following label instructions and application rate guidance. Due to certain restrictions on the use of these insecticides, you may need the services of a licensed pesticide application business.
Products containing either imidacloprid or dinotefuran as the active ingredient and labeled for use on adelgids are effective in combatting the insect.
No matter which treatment you select, be sure your treatment plan will include 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. This includes trees on your property as well as neighboring properties. It's a good idea to discuss treatment plans with neighbors and coordinate efforts when possible.
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. 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 pesticide to enter or runoff into storm drains, drainage ditches, gutters or surface waters.
More information on do-it-yourself treatment can be found in the MSU Extension bulletin: Guidelines for homeowner treatments of hemlock trees infested with hemlock woolly adelgid, available at Michigan.gov/HWA.
|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. Look for one that is licensed in the "ornamental" category (3B).
Hemlock woolly adelgid's cottony, white ovisacs will linger for a time following treatment. If trees are treated in the spring, check new growth in late fall or winter for any fresh signs of infestation.
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 five years.
|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.
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 suspect signs of the insect.
You also can take pictures, note the tree's location and email the information to the Michigan Department of Agriculture and Rural Development at MDA-Info@Michigan.gov 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. A state interior quarantine makes it illegal to move hemlock anywhere within or out of Allegan, Ottawa, Muskegon, Oceana, or Mason counties. Currently there is no known hemlock woolly adelgid in Benzie County, as the single-tree detection was destroyed. Waste hemlock material in the quarantined counties may be moved to approved disposal sites within the quarantine zone.
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. Suggested captions follow.
Infested branch: Round, white hemlock woolly adelgid ovisacs are found on the undersides of branches near the base of the needles.
Hemlock tree: Hemlock trees are generally cone-shaped with lacy or feathery branches.
Tree injection: A certified pesticide applicator prepares to inject an infested hemlock tree with pesticide.
Magnification: Hemlock woolly adelgids are small and difficult to see. It is easier to identify their white, cottony ovisacs . Photo courtesy of Lorraine Graney, Bartlett Tree Experts, Bugwood.org./