A mysterious disease is spreading quickly among Maine’s beech trees.
Called beech leaf disease, it can kill all types of beech trees, or weaken them so that they’re susceptible to other pests. After first being found in the state just four years ago, it is now known to be in every county except Franklin.
Maine’s forest service found the disease in 119 new towns last year and 12 more so far in 2025. So far, the confirmed sites are along the coast up to the border of Washington County and extending north. The service expects to locate cases in many more Maine towns this year, it said in a newsletter last week.
Many unknowns remain about the disease, including how it spreads and how to stop it, but scientists believe it’s associated with nematodes that travel in the fall when it’s raining or windy.
Maine trees are facing a number of spreading invasive threats, including emerald ash borer, spruce budworm and hemlock woolly adelgid. Beech trees are a dominant feature of the state’s hardwood forests, a timber product and a source of habitat and food for wildlife, from bears to butterflies; some have already been at risk for decades from another condition called beech bark disease.
The most common type of forest in Maine is dominated by beech, birch and maple – covering 7.2 million acres in 2018 – and in New England. Beech trees have also become more dominant in the region in recent decades, University of Maine researchers found in 2018.
American beeches are vulnerable to an insect called the beech scale, which in turn makes the trees susceptible to fungi that cause beech bark disease.
Some beech trees with smooth bark are resistant to the bark disease and are targets for preservation, according to the Maine Forest Service.
The leaf disease appears as dark bands between the veins of leaves, which might also look shriveled or deformed.
Research for prevention is underway. For now, it’s recommended to avoid moving any materials from affected trees or the soil around them. Some organizations suggest cleaning shoes after leaving an area that has the disease, to reduce the risk of transporting nematodes.
But scientists don’t necessarily recommend cutting down trees with beech leaf disease that are still alive, because some of them might be resistant, and keeping more genetic diversity can mean more resilience to the threats.