Invasive hemlock woolly adelgid found in northern Benzie County

Contact: Rob Miller, 517-614-0454 or Joanne Foreman, 517-284-5814
Agency: Natural Resources

Feb. 19, 2021

The Michigan Department of Agriculture and Rural Development recently verified a new detection of invasive hemlock woolly adelgid at the Sleeping Bear Dunes National Lakeshore in northern Benzie County. To date, a survey of the surrounding area has found just one infested tree in the Platte River Campground, a popular destination within the National Lakeshore.

Hemlock woolly adelgids are small insects that use their long, siphoning mouthparts to extract sap from hemlock trees. Their feeding weakens needles, shoots and branches. Over time, tree growth slows, and trees take on a grayish-green appearance. Without treatment, infested trees die within four to 10 years.

These insects are considered invasive because they are not native to Michigan and can cause significant harm to the state’s hemlock resource, estimated at 170 million trees.

Hemlock branch with hemlock woolly adelgid ovisacsWith support from the Great Lakes Restoration Initiative, National Lakeshore staff began surveying high-use areas throughout the park in January, looking for the invasive insect that, in October 2020, was detected in Ludington State Park, approximately 70 miles south of Sleeping Bear Dunes. The survey crew worked alongside a team from the Northwest Michigan Invasive Species Network (ISN), which has been surveying hemlock trees within 5 miles of Lake Michigan since 2018 as a part of a Michigan Invasive Species Grant Program early detection project.


On Feb. 4, surveyors found round, white ovisacs characteristic of the hemlock woolly adelgid on one tree in the Platte River Campground. A sample sent to the U.S. Department of Agriculture was verified the following day.

Michigan has been combating hemlock woolly adelgid since 2006 and has current infestations in Allegan, Ottawa, Muskegon, Oceana and Mason counties.

How does it spread?

Hemlock woolly adelgid likely arrived in Michigan on infested nursery stock from northeastern states. Though the tiny insects don’t move far on their own, they can be blown by wind or “hitchhike” on birds or mammals that come into contact with an infested branch. In a similar way, cars, boats or RVs parked under infested trees may be able to transport the insects to new locations.

A statewide effort

Workers survey for hemlock woolly adelgid in a snowy forestIn 2016, Michigan’s Hemlock Woolly Adelgid Coordinating Committee brought together researchers, technicians and field staff from universities and federal, state and local agencies to develop and carry out a statewide response effort to protect hemlock trees, an important component of Michigan’s northern forest ecosystem. The result has been a coordinated effort of research, outreach, surveying, data collection and targeted treatment on both public and private lands focused on slowing the spread of the invasive insect.


Rob Miller, an invasive species prevention and response specialist with MDARD, coordinates the statewide program. According to Miller, this new detection underscores the importance of the survey effort, which spans the Lake Michigan shoreline from the Indiana border to the Upper Peninsula.

“While we never want to find a new infestation, discovering it early on, as in this case, when we have a reasonable chance of containing it and saving trees, is really the purpose of this program,” said Miller.

Response is underway

Since the initial detection at the National Lakeshore Feb. 4, crews have completed a survey of all hemlocks within an 800-foot radius of the infested tree as well as a grid search of the broader vicinity, finding no additional infestations so far. Partners are making plans to treat the infested tree and other nearby hemlocks in spring 2021.

Since January, ISN has logged 388 survey acres across its service area, which includes Manistee, Benzie, Leelanau and Grand Traverse counties, and those efforts will continue through early spring. Hemlock surveys in other lakeshore counties are being conducted by local Cooperative Invasive Species Management Areas and state agency staff.

ISN is contacting private landowners within the vicinity of the Platte River Campground to request permission to survey for the invasive insect.

Free surveys available

All landowners and managers of properties within 5 miles of the Lake Michigan shoreline can take advantage of the no-cost hemlock survey program. Residents in the ISN’s service area can complete an online hemlock woolly adelgid survey request form or contact Audrey Menninga, invasive species specialist, at 231-941-0960 ext. 18 or AMenninga@GTCD.org. Those in other counties should contact their local CISMA by visiting MichiganInvasives.org.

Help the survey effort

Hemlock treeIf you are planning to spend time outdoors this winter, you can help look for and report hemlock woolly adelgids. Look on the undersides of hemlock branches for evidence of round, white ovisacs near the base of the needles.


Up close, ovisacs look like balls of spun cotton and may appear alone or in clusters. The short video Hemlock Woolly Adelgid: Invasive Species in Michigan provides helpful identification tips.

Other, less damaging pests easily can be mistaken for hemlock woolly adelgid. Be sure to review photos and descriptions of common hemlock woolly adelgid look-alikes at Michigan.gov/HWA. Help in identifying eastern hemlock trees is also available at the same site.

How to report

Trees infested with hemlock woolly adelgid should be reported by one of the following means:

Be prepared to report the location of infested trees and, whenever possible, take one or two pictures of infested branches to help confirm identification. To avoid spreading hemlock woolly adelgid, do not collect sample branches or twigs.

The MISIN smartphone app will take a GPS location point if a report is made at the site; it also will allow you to upload photos with a report.

Prevent further spread

As more and more people take to the outdoors, the potential for spreading hemlock woolly adelgid and other invasive species also grows.

“While human movement isn’t the only way invasive species spread, it is the most common,” said Julie Christian, Natural Resource Division manager at the National Lakeshore. “If you’re headed outdoors, it’s more important than ever to take simple measures to protect the places we all love. ‘Play, Clean, Go’ is a good motto to remind us to clean gear and vehicles before we hit the road. Parking in designated areas and staying on trails also helps to protect natural areas. Remember to leave firewood at home and buy it locally at your destination.”

For more information on hemlock woolly adelgid and other invasive species in Michigan, and to find out what you can do to help prevent them, visit Michigan.gov/Invasives.


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

/Note to editors: Accompanying photos are available below for download. Suggested captions and photo credit information follow:

Branch: Surveyors recognized the small, white dots at the base of the needles on the underside of this infested branch in the Platte River Campground as a sign of hemlock woolly adelgids. Photo courtesy of Sleeping Bear Dunes National Lakeshore.

Survey: Hemlock woolly adelgid survey crews work throughout the winter, often making their way through deep snow in remote and rugged areas. Photo courtesy of West Michigan CISMA.

Hemlock tree: Hemlock trees are generally cone-shaped with lacy or feathery branches./