Hemlock-killing insect found in 3 Michigan counties


LANSING, Mich. — The Michigan Department of Agriculture recently confirmed small infestations of the hemlock woolly adelgid at sites in Emmet, Macomb and Ottawa counties.

“Nursery operators, landscapers and homeowners should never accept hemlock from quarantined areas, and never accept hemlock without proper certification,” said Ken Rauscher, MDA Pesticide and Plant Pest Management Division director.

“Examine your hemlock for the presence white, cottony masses on the underside of the branches where the needles attach. If you suspect HWA, contact MDA immediately.”


The positive sites in Macomb and Ottawa counties were discovered by two alert arborists who reported their suspicions to MDA. The positive site in Petoskey was discovered by an MDA inspector upon re-inspection of a previously negative invoice tree from the 2006 detection.

The trees in Petoskey have been removed and replaced by the landscaper who inadvertently brought them into the state in 2006 and insecticides have been applied.

“These detections underscore the importance of citizen involvement in exotic pest detection,” said Rauscher. “Without these alert and conscientious individuals, these detections may have gone unnoticed for months, or even years, making eradication of this devastating pest much more unlikely.”

These infestations represent the first detections of HWA in Michigan since 2006, when it was found in hemlock nursery stock grown in West Virginia and planted for residential landscaping in the Harbor Springs area.


This population was eradicated, and the area was subjected to several years of intensive pesticide treatments and surveys. The new infestations are also believed to originate from hemlock nursery stock originating from HWA-infested areas of the U.S.

The infested trees at each site have been removed and destroyed. Nearby trees are being treated with pesticides and surveys are being performed to determine if HWA has spread.

“MDA is requiring removal of positive trees and treatment with an approved insecticide and will also conduct survey activities where HWA has been confirmed,” said Rauscher. “Homeowners should be on the lookout for white cottony masses at the base of the needles and report any suspects to MDA.”

HWA is a small, aphid-like insect that uses its long, siphoning mouthparts to extract sap from hemlock trees. Native to eastern Asia, HWA was discovered in Virginia in 1951, and has since spread over an area from Georgia to Maine, decimating hemlock stands across much of the eastern U.S.


More than 100 million hemlock trees are present in Michigan forests, providing valuable habitat for a diversity of animals, including birds, deer and fish. These trees are critical to the ecology and aesthetics of Michigan’s northern forests.

Michigan law restricts the movement of hemlock into the state, and includes a complete ban on the movement of hemlock from infested areas. Details on this quarantine and more information on HWA can be found at www.michigan.gov/mda.


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