Hemlock Woolly Adelgid Reaches Acadia National Park

Wool from the hemlock woolly adelgid on an eastern hemlock branch in the Sieur de Monts area of Acadia. NPS photo by Jesse Wheeler.

The pest

The hemlock woolly adelgid is an invasive forest pest that has killed great numbers of hemlock trees since it arrived in the eastern United States several decades ago. It spread naturally into southern Maine in the early 2000s, but took another 20 years to reach the edge of Acadia National Park.

Where it has been found

The good news: the infestations were caught early, so the trees at these sites are still healthy.

Known hemlock woolly adelgid sites in Acadia, as of January 31, 2023. NPS map by Emma Lanning.

What's being done

• In the park: ahead of the pest's arrival, Acadia's Invasive Plant Management Team began mapping hemlock stands and choosing priority areas to protect — work that continues. Crews are also trimming hemlock branches that could brush against cars, cyclists or walkers along roads and trails.
• Next door: the park hasn't yet released biological controls or used chemical treatments, but its neighbors have acted. In October 2022, the Land and Garden Preserve released Laricobius osakensis predator beetles along Jordan Stream beside the park. The Maine Forest Service has recommended the adjoining part of the park as a good candidate for another release.

The outlook

Knowledge of the adelgid — its life history, its risks and how to treat it — has grown a great deal. Today's tools give Acadia's hemlocks a more hopeful outlook, though forest managers still face a hard road. The park's species profile explains how to recognize and manage the pest.

Think you've found it in Acadia? Report it to the park's vegetation program.

Sources

Based on "Hemlock Woolly Adelgid Confirmed in Acadia National Park," National Park Service; a work of the United States government in the public domain.