Save MI Hemlocks


West Michigan Conservation Network partners are teaming up to launch efforts to control and eradicate Hemlock Woolly Adelgid. Funding for the work in West Michigan has been obtained by a grant distributed through the EPA’s Great Lakes Restoration. Grant funds will be used to conduct surveys, track infestations, provide outreach and education for public and private landowners, manage data, and provide rapid response and treatment of infested sites throughout Lake Michigan’s coastal zone.

What is Hemlock Wooly Adelgid?   

Hemlock Wooly Adelgid (HWA) is one of Michigan’s newer invasive pests.  HWA – tiny insects that feed on sap from hemlock shoots and branches – can kill needles, shoots and branches. Over the course of four to ten years, growth slows as trees become less vigorous and eventually the tree dies. Other stress factors, such as drought, can cause a hemlock to reach mortality more quickly.

Measuring a mere 1.5mm in length, HWA is difficult to see but can be identified by the presence of white, woolly masses, called “ovisacs.” These protective masses, which cover the insects and their eggs, are more easily detected in late fall through spring. All HWA reproduce asexually and complete two life cycles per year.

What is at Risk? 

More than 170 million hemlock trees growing in forests, along stream and riverbanks, and in landscapes throughout the northern lower peninsula and the upper peninsula. Hemlocks are among the oldest living trees in Michigan and provide critical habitat and winter cover for many species.

Hemlocks are also imperative for Michigan cold-water streams because they provide the shade necessary to keep water cool for species such as trout and salmon.

How does HWA Spread? 

HWA can move from tree to tree in multiple ways, including:

  • Birds and wildlife
  • Recreational vehicles
  • Equipment and field gear
  • Infested nursery stock
  • Infected brush piles

Signs of an HWA Infection: 

The presence of HWA is indicated by:

  • White, cottony masses about ¼ the size of a cotton swab attached to twigs at the base of the needles, on the underside of the branch
  • Needle loss and branch die back with no new growth
  • Gray-tinted foliage

The West Michigan HWA Taskforce has created a resource to help spread the word about the importance of identifying, reporting and taking action to stop the spread of HWA. A printable version of this is available on Downloadable Resources.

Additional Resources:

Save MI Hemlocks

State of Michigan Invasives