The hemlock wooly adelgid, or HWA, is a sesame seed-sized invasive insect from Asia that’s been threatening eastern hemlock in Ottawa County parks for almost 10 years. The trees grow along the shore of Lake Michigan, stabilizing dune systems.
Staff, volunteers and park visitors have continued detecting and reporting populations of HWA throughout the park system. If left untreated, HWA can kill a hemlock in about four to seven years.
Ottawa County Parks and Recreation staff have been treating affected trees with insecticide injections, which protects hemlocks for about four to six years.
Treatment areas have included Rosy Mound Natural Area, with 96% of nearly 2,000 hemlocks treated, Hemlock Crossing, with 89% of nearly 180 hemlocks treated, and Stearns Creek, with 51 trees treated, and more scheduled for tagging next season.
The infested area has been expanding yearly, now reaching as far north as Leelanau County.
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