Maine Battles Invasive Forest Pests and Diseases

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Maine is facing a range of forest pests and diseases, including the hemlock woolly adelgid, browntail moth, red pine scale, emerald ash borer, beech leaf disease, and spruce budworm. While some pests have seen declines due to cold weather and control measures, officials warn that climate change and warming winters could allow these invasive species to spread further inland, posing ongoing threats to Maine's forests.

Why it matters

Maine's forests are crucial to the state's ecology, economy, and culture. Invasive pests and diseases that damage or kill off key tree species like hemlocks, ash, and beech can have far-reaching impacts, from disrupting wildlife habitats to threatening the state's timber industry and traditional practices like Wabanaki basket-making. Monitoring and managing these threats is essential to protecting Maine's forest ecosystems.

The details

The hemlock woolly adelgid, an insect that feeds on hemlocks, has been concentrated in Maine's midcoast region for over two decades. Cold winters have helped slow its spread, but officials warn that warming temperatures could allow the adelgid to move further inland. The invasive browntail moth, whose caterpillars can cause rashes and respiratory issues, has seen a steep decline in recent years due to control efforts, but other pests like the red pine scale and emerald ash borer continue to spread, quickly killing off host trees. Beech leaf disease has also engulfed many of Maine's beech trees in just five years, compounding issues with the existing beech bark disease. Meanwhile, the spruce budworm has been cropping up in Aroostook County, prompting the state's 'early intervention strategy' of detection and targeted pesticide treatments.

• Over the past couple of years, deep freezes and control measures have slowed the spread of some prominent Maine forest pests and diseases.
• In 2025, emerald ash borer populations migrated north to three new counties: Somerset, Waldo and Hancock.
• Beech leaf disease has engulfed and defoliated a vast number of Maine's beech trees in just five years.
• A less prevalent outbreak of the endemic spruce budworm has been cropping up in Aroostook County.

What they’re saying

What’s next

The Maine Forest Service will continue its efforts to monitor and manage these forest pests and diseases, including releasing predator insects to control the hemlock woolly adelgid and using targeted pesticide applications to curtail spruce budworm outbreaks.