Beech bark disease: what the agencies record

This page reports what the official source says. It is not legal advice: ask the office named here. It does not identify what is wrong with any tree and does not say what should be done about one. None of the three pages read lists beech bark disease as regulated. The Wisconsin Department of Natural Resources asks that suspect trees be reported. Each section names its source, all read on October 9, 2026. The full list of diseases is on the tree diseases page.

Two organisms, one disease

All three sources say the disease needs both an insect and a fungus. The University of Maryland Extension describes a very small, non-native armored scale called beech scale, Cryptococcus fagisuga, whose feeding makes tiny wounds in the bark, and a canker-causing fungus of the genus Neonectria, including Neonectria faginata and Neonectria ditissima. The Wisconsin Department of Natural Resources, called Wisconsin DNR, says the disease only happens when both are present: the tree is infested by the scale and then colonized by one of several Neonectria fungi. Natural Resources Canada, called NRCan, names the fungus as Nectria coccinea and says the combined action of the scale and the fungus leaves most affected beech to die, directly or through attack by other pathogens.

On the fungi, Wisconsin DNR says Neonectria ditissima is a native North American fungus causing a target canker on weakened hardwoods, and that N. faginata is also believed to be native to North America. Maryland says by itself the scale usually does not kill the tree, though heavy feeding may weaken it, and that the fungus can ultimately stunt and kill beech.

Hosts

NRCan lists American beech as the main host. Wisconsin DNR names the species affected as American beech, European beech, Chinese beech and Oriental beech. Maryland says the disease affects beeches of the genus Fagus, and threatens ornamental beeches in managed landscapes as well as forest trees.

The scale stage

Maryland says the first detectable sign of risk is the scale's white body covering against the gray bark, in scattered groups on the trunk and branches that spread as the population builds, with yellow newly hatched crawlers carried from tree to tree mainly by wind. The young molt twice and become adult females in the spring, and in midsummer the all-female population lays eggs without mating and dies. Eggs hatch from late summer to early winter. Wisconsin DNR gives the scales as 0.5 to 1 mm long and related to aphids, with eggs laid in summer and hatching in the fall, and says the young lose their legs, become covered in woolly wax and stay on the bark for life. NRCan says the woolly covering makes the tree look as if covered with snow. Wisconsin DNR says scale populations can rise to high levels in two or three years, that natural movement is estimated at six miles per year, and that the scale typically appears several years before disease symptoms.

The fungus stage and signs

NRCan says fungal spores spread by rain splash or wind and enter through the wounds the scale makes. The bark first shows a depression, then cankerous blisters, and on severely affected trees the cankers merge. Maryland says the fungus kills the inner bark and can rot the outer wood, girdling the tree. It lists tarry spots on the bark as a sign of wounds or infection. Wisconsin DNR says the fungus kills living tissue under the outer bark, with an orange color at the front edge of the fungal growth, that some trees produce a brown sap at dead spots, and that the canker makes the bark look rough.

Harm to beech stands

Wisconsin DNR says that as the disease first moves into a forest, large beech usually die within a few years of scale buildup, a first wave it calls the killing front. After it passes, the forest usually holds some surviving large beech and many small beech sprouted from the roots of dead trees, often disfigured. It adds that decay fungi and wood-boring insects can invade diseased trees. NRCan also says tree mortality is often caused by other pathogens such as Hypoxylon fungi, or by other insects. Maryland says that in some forest areas beech mortality has approached 50 percent.

History and where it is recorded

Point	What is recorded	Source
Europe	The disease occurred in Europe before 1849. The scale was thought the sole cause of tree death until 1914, when the fungus was found to be involved	Maryland
Nova Scotia	The scale was accidentally introduced from Europe around 1890; by the 1930s the scale and a Neonectria fungus were killing trees in eastern Canada and Maine	Wisconsin DNR; Maryland gives the early 1930s
Eastern United States	Pennsylvania northward to Nova Scotia, plus separate infestations in six other states: Michigan, Tennessee, North Carolina, Virginia, West Virginia and Maryland	Maryland
Michigan and Wisconsin	Found in northern Michigan in 2000 and in Door County, Wisconsin, in 2009; beech scale confirmed in 13 Wisconsin counties; tree mortality from the fungus observed in Door County and confirmed in Menominee County in 2025	Wisconsin DNR

Regulated status and reporting

None of the three pages names a quarantine for beech bark disease. Wisconsin DNR asks readers to report suspect trees, covered with white woolly spots, to the local DNR office or to DNR forest health staff, and its page lists the department's general line, 1-888-936-7463. For other places, see the guides on reporting a pest in Canada and the United States. For the host tree, see American beech.

Management as the sources list it

Maryland and Wisconsin DNR agree that there is no practical control in a forest setting except salvage cutting, that insecticide products can be used against the scale on ornamental beeches, and that a small share of trees appear resistant to the scale. This page gives no product names, rates or timings. For who may apply pesticides, see pesticide licences.