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Invasive Species: Hemlock Woolly Adelgid

Hemlock Woolly Adelgid

(Adelges tsugae)
*Detected in Michigan*


What to look for:

  • Small, round, white, cottony masses, 1/16" to 1/4". 
  • Found on the twig at the base of the needles on the underside of hemlock tree branches.
  • Present year-round but most visible November through July.
  • Note that hemlock woolly adelgid infests eastern hemlock trees, not pines or spruces.

Eastern hemlock branch infested with hemlock woolly adelgid

Hemlock woolly adelgid forms round, white ovisacs on the undersides of eastern hemlock twigs.

Hemlock woolly adelgid ovisac close-up

Close-up of a hemlock woolly adelgid ovisac. Photo courtesy of Lorraine Graney,

How to identify eastern hemlock trees:

  • Eastern hemlocks have short, flat green needles with two white stripes on the underside.

Hemlock needles with white stripes on the underside

  • Eastern hemlock needles grow singly (not in clusters) from the sides of twigs, giving the branch a flat appearance.

Hemlock branches appear flat

Report hemlock woolly adelgid

NOTE: Many other things may look like hemlock woolly adelgid. Please review hemlock woolly adelgid look alikes (printable PDF) before reporting

If you notice white, waxy material at the base of the needles on hemlock trees, to prevent spread, do not remove potentially infested material from the site. Take photos, note the location of the affected trees and report it to:

About this species

Habitat: Hemlock woolly adelgid infests eastern hemlock trees and has been found in Michigan in both forest and landscape settings. Eastern hemlock is found naturally in moist forest environments and along streams and water bodies. Hemlocks also are used in home, urban and park landscapes in many areas.

Native Range: East Asia.

U.S. Distribution: Hemlock woolly adelgid has been identified in at least 20 states in the Eastern U.S., including portions of Michigan.

Michigan Distribution: Active populations of hemlock woolly adelgid are present in areas of Allegan, Antrim, Benzie, Mason, Muskegon, Oceana and Ottawa counties in West Michigan and Washtenaw County in southeast Michigan. The maps below represent all known hemlock woolly adelgid infestation zones as of the date specified on each map. Areas lacking data either have been surveyed with no hemlock woolly adelgid present or have yet to be surveyed. Survey efforts are ongoing.

Local Concern: Michigan is home to an estimated 170 million eastern hemlock trees which provide important habitat and protect against erosion along rivers and streams. The hemlock woolly adelgid sucks sap from hemlock needles, killing needles, shoots and branches. Infested hemlocks become less vigorous and may turn grayish-green. Left untreated, hemlock woolly adelgid can cause tree death in 4-10 years.

Means of Introduction or Spread: Hemlock woolly adelgid can be moved from tree to tree by birds, other wildlife, the wind, and on gear, equipment, clothing, infested nursery stock or other hemlock materials. Hemlock woolly adelgid can be moved when infested branches are trimmed and disposed of, and also by vehicles or equipment brushing against infested branches.

Quarantine Information: Michigan's hemlock woolly adelgid interior and exterior quarantines regulate the movement of certain nursery stock and forest products within and from infested counties in Michigan (interior), and into the state from infested counties in other states (exterior).

Treatment: Certain insecticides are successful in treating hemlock woolly adelgid if used correctly. A qualified arborist, such as one certified by the International Society of Arboriculture, can diagnose and treat infested trees. If you are able to undertake treatment on your own, follow the guidance provided below.

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