Invasive Hemlock Pest Found at More Sites in West Michigan

Agency: Agriculture and Rural Development

MDARD asks public asked for continued help in looking for invasive pest

For immediate release: September 16, 2015

Program contact: John  Bedford, 517-284-5650
Media contact: Jennifer Holton, 517-284-5724

Lansing – Thanks to an alert citizen working in the area, the Michigan Department of Agriculture and Rural Development today confirmed hemlock woolly adelgid, an invasive tree-killing pest discovered in Ottawa County in June, has now been found at locations in southwestern Muskegon County. The finds in Ottawa and Muskegon counties are the first instances of HWA occurring in native forest hemlock. 

MDARD and its partners have been actively monitoring and controlling HWA since 2001, but until this year, all HWA infestations found in Michigan were restricted to nurseries and hemlock landscaping. Each infestation was treated, eradication activity took place and continual survey occurred after eradication activities were wrapped up. Central to this MDARD’s HWA response plan is continued surveillance and reporting of new infestations.  

“Once again, citizen involvement played a central role in early detection. Continued citizen involvement and citizen reporting is crucial for the management of this pest or any other exotic pest,” said Gina Alessandri, MDARD’s Pesticide and Plant Pest Management Division Director. “Examine your hemlock for HWA, and if you find something suspicious contact MDARD immediately.”

Hemlock can be distinguished from other Michigan conifers by its flattened rows of short, flat needles arising from the sides of the branches. The needles are rounded at the end and soft to the touch. Their undersides are whitish in color. Hemlock cones are small – an inch long or less. Hemlock trees are typically green in color, but in advanced HWA infestations, twig and branch mortality can occur, giving infested trees a grayish hue. The small cottony masses characteristic of HWA are found on the underside of the branch at the base of the needle; they are never found on the needles themselves.

HWA can be very difficult to detect at low population levels because the insect is so small. The movement of hemlock materials (trees, branches and twigs) could spread HWA; these should not be removed from properties within this area. Residents are also advised to keep birdfeeders away from hemlock trees because birds can spread the pest.  

Since its discovery in Virginia in 1951, HWA has spread rapidly across most of the native range of hemlock in the eastern U.S., decimating hemlock forests from Georgia to Maine. It remains a valuable landscape tree, grown extensively – and usually under strict pesticide treatment regimens to control HWA – in southern Appalachian states. From there hemlock trees are widely distributed in the nursery and landscape trade.

To protect Michigan’s hemlock forests and the wildlife – including birds, mammals, and even fish – they support, MDARD has maintained a strict quarantine against out-of-state hemlock since 2002. Current and past infestations in Michigan are likely the result of hemlock from these areas shipped into Michigan prior to, or in violation of, this quarantine.

Read MDARD’s “Hemlock Woolly Adelgid Quarantine”.

To report a possible HWA detection, contact MDARD at 800-292-3939 or

For information on how to tell hemlock from other common evergreen trees in Michigan, click here.

Additional information on HWA, including pictures, and other invasive and exotic species threatening Michigan can be found at

 hemlock woolly adelgid
Hemlock woolly adelgid
Adelges tsugae 
Photo by Connecticut Agricultural Experiment Station Archive



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