Invasive hemlock woolly adelgid found in Manistee and Van Buren counties

Invasive hemlock woolly adelgid found in Manistee and Van Buren counties

The Michigan Department of Agriculture and Rural Development (MDARD) has confirmed new detections of invasive hemlock woolly adelgid (HWA) in Manistee and Van Buren counties.

With these new detections,11 Michigan counties have active hemlock woolly adelgid infestations:

• Allegan
• Antrim
• Benzie
• Manistee
• Mason
• Muskegon
• Oceana
• Ottawa
• Van Buren
• Washtenaw 

Manistee County Detection

Hemlock woolly adelgid was detected by the Mason Lake Conservation District on February 3, 2025, during a routine HWA survey. The U.S Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed the detection on February 6, 2025. Working closely with MDARD and other partners, the conservation district conducted surveys near the northern edge of infestation. The HWA detection is about 0.5 miles north of the Mason and Manistee County line near Lake Michigan.

Van Buren County Detection

On March 3, 2025, the Michigan Department of Natural Resources (DNR) Parks and Recreation Division’s Forest Health Technicians detected two hemlock trees infested with HWA in Van Buren State Park (see attached photos). Samples collected from the infested trees were positively confirmed by USDA APHIS on March 4, 2025. Forest health technicians are in the process of determining the full extent of the infestation and plan to treat the infested trees this summer. Park visitors are advised to stay on designated trails to limit the risk of accidently spreading HWA. The trees were previously surveyed in late November of 2024, with no ovisacs detected at that time.

Hemlock Woolly Adelgid Identification

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.

Hemlock woolly adelgid can be identified by looking on the undersides of hemlock branches for evidence of round, white ovisacs near the base of the needles. Up close, ovisacs resemble cotton balls and may appear alone or in clusters. For assistance in identification, see MDARD’s short video Hemlock Woolly Adelgid: Invasive Species in Michigan.

It's important to note that 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.

Report Suspected Infestations

Report any suspected HWA infestations by:

• Emailing MDARD at MDA-Info@michigan.gov or calling the Customer Service Center at 800-292-3939.
• Using the Midwest Invasive Species Information Network (MISIN) online reporting tool or downloading the MISIN smartphone app and reporting from your phone.

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.

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.