MDARD updates state's two hemlock woolly adelgid quarantines

Contact: Program contact: Robin Rosenbaum, 517-490-1301 Media contact: Jennifer Holton, 517-284-5724
Agency: Natural Resources

Sept. 18, 2020

Revisions aim to help better protect Michigan’s hemlock trees

LANSING, MI – The Michigan Department of Agriculture and Rural Development (MDARD) revised both the state of Michigan’s interior and exterior hemlock woolly adelgid (HWA) quarantines. The new quarantines are effective on September 24, 2020.

“These quarantines are designed to protect the 170 million hemlock trees that live in Michigan’s forests,” said MDARD Director Gary McDowell. “According to the USDA Forest Service, hemlock trees have a strong impact on streamside habitat conditions and stream health. Loss of hemlock could result in a rise in water temperatures in streams and an increase in soil erosion, something Michiganders certainly don’t need to further experience."

Hemlock branch infested with hemlock woolly adelgid“If left unchecked, hemlock woolly adelgid could spread throughout Michigan’s hemlock trees, causing significant loses and affecting the timber and lumber industries, nursery and landscaping industries, the Christmas tree industry, and the tourist industry,” added Mike Philip, MDARD’s Pesticide and Plant Pest Management Division director. “Hopefully, these revisions will keep the pest from moving to new areas in the state and slow the spread within the five currently affected counties.”

The previous interior hemlock woolly adelgid quarantine only regulated movement of hemlock in Allegan, Muskegon, Oceana, and Ottawa counties. The quarantine was updated to include Mason County after the pest was identified there in February 2020. It was also revised to allow movement of hemlock yard waste within the regulated counties without requiring a compliance agreement, provided the material is safeguarded during transport and is taken to disposal sites located at least 100 yards from any hemlock trees.

Hemlock woolly adelgid ovisac with crawler on a hemlock twigAlso, MDARD updated the state’s exterior HWA quarantine, adding clarification to the responsibilities for notifying the department on incoming shipments. Out-of-state firms shipping hemlock nursery stock into Michigan must provide information to MDARD in advance of the shipment including a plant health certificate from the state of origin and details on the destination in Michigan.

The updated HWA quarantines are available on the department’s website. Suspected quarantine violations can be reported by emailing Additional information about hemlock woolly adelgid is available at

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 & Rural Development.

Branch: An eastern hemlock tree branch infested with hemlock woolly adelgid. Photo courtesy of Steven Katovich, USDA,

Ovisac: Tiny hemlock woolly adelgids build round, white ovisacs to protect their eggs.  Ovisacs are most visible from fall to spring on the underside of hemlock branches. Photo courtesy of Lorraine Graney, Bartlett Tree Experts,