Beech bark disease (Neonectria spp.)

Synonyms: Neonectria faginata, Neonectria ditissima, Nectria coccinea var. faginata, Nectria galligena

Common Names: BBD, beech bark disease complex

Description:

Beech bark disease (caused by Neonectria fungi) is a deadly disease of beech trees that works as a team of two pests [1]. First, a tiny non-native insect ? the woolly beech scale ? feeds on the bark and makes small wounds; then Neonectria fungi enter through those wounds and kill the inner bark, forming cankers that can girdle and kill the tree [1][3]. MISIN tracks it because it kills American beech across whole forests, and people spread it by moving infested firewood, logs, and nursery trees [1][2].

Identification:

Beech bark disease shows itself on the trunk and branches of beech trees, so you identify it by the marks on the bark rather than by a plant or animal you can pick up. The first sign is usually a white, woolly or felt-like wax on the bark ? these are colonies of the beech scale insect, and heavy infestations can make the trunk look whitewashed [1][3]. Where the fungus has taken hold, the smooth gray beech bark becomes blistered, cracked, pocked, and sunken with cankers, and you may see clusters of tiny bright red dots, smaller than a pinhead, which are the fungus's fruiting bodies [1][3]. As the disease advances, the crown thins and dies back, and weakened trunks can break off in wind ? a hazard known as "beech snap" [1].

The white woolly scale is easiest to see in fall and winter on the trunk and the undersides of branches [3]. The tiny red fungal bodies are most visible in fall on infected bark [3]. Trees in an area usually begin to die about three to six years after the scale first arrives [2].

At-a-glance cues:

1. White, woolly or felt-like wax patches on beech bark (the scale insect) [1][3]
2. Blistered, cracked, pocked, or cankered bark on a normally smooth gray beech trunk [1][3]
3. Clusters of tiny, bright red, pinhead-sized fungal fruiting bodies on the bark [1][3]
4. Crown dieback, and weakened trunks that snap off ("beech snap") [1]

Habitat:

Beech bark disease lives on beech trees, so its "habitat" is its host ? American beech (Fagus grandifolia), the smooth, gray-barked tree of eastern forests, as well as the European beech often planted in yards and parks [1]. Wherever beech grows ? in forests, woodlots, parks, and home landscapes ? the disease can take hold once the beech scale insect arrives and the Neonectria fungi follow [1][3].

The disease is a two-part complex of introduced and native organisms. The woolly beech scale came from Europe, reaching Nova Scotia around the 1890s on imported beech saplings and the United States by about the 1930s, and it has spread south and west ever since [1]. It is now established across the northeastern United States and the Great Lakes region [1].

Reproduction:

Beech bark disease spreads in two linked ways, and people play a big role. The beech scale insect moves on its own as tiny crawlers that are blown by the wind and carried on birds and animals, while the Neonectria fungi spread by spores carried on wind and rain [1][3]. But the fastest long-distance jumps happen when people move the disease ? on infested firewood, logs, and nursery beech trees [1]. That is why a beech far ahead of the main infestation often turns out to have arrived on moved wood [1].

There is no "seed-set" timing to target here as with a weed. The practical timing is about prevention and watching: do not move beech wood, and do not wound beech bark, since fresh wounds give the fungus another way in [1][3]. Once the scale arrives in an area, trees typically begin dying within about three to six years [2].

Impact and Damage:

Beech bark disease is not a danger to people or pets ? it harms beech trees [1]. For a homeowner with beech in the yard, it can disfigure and slowly kill a prized shade tree, and a badly weakened beech can drop limbs or snap off in a storm, creating a hazard near homes and walkways [1]. There is no cure once a tree is heavily infected [1].

In forests, the disease kills large numbers of mature beech, opening the canopy and changing the makeup of the woods [1]. Dying beech often send up dense thickets of root sprouts, but these young stems are also susceptible, so the disease tends to replace big, healthy beech with struggling thickets rather than restoring the forest [1]. Losing mature beech also means losing beechnuts, an important fall food for black bears, deer, turkeys, and many other animals [1]. A small fraction of beech trees appear naturally resistant and stay free of the scale, and protecting these trees is a key to the forest's long-term recovery [3].

Similar species:

Beech leaf disease (caused by the nematode Litylenchus crenatae mccannii) is a newer, separate disease of the same beech trees, so the two are easily mixed up by name and host. You can tell them apart by where the damage is: beech leaf disease shows as dark, thick bands between the veins of the leaves, while beech bark disease attacks the bark and trunk.

Woolly aphids and other cottony scale insects can also leave white, woolly or cottony wax on tree bark and twigs, which may be mistaken for the beech scale. These are told apart by the host tree and by the felted, crusty colonies of beech scale packed into bark cracks on beech specifically, rather than the fluffier tufts of woolly aphids on other trees.

Monitoring and rapid response:

Signs to watch for:

1. White, woolly wax patches on beech bark, most visible in fall and winter [1][3]
2. Blistered, cracked, or cankered bark and clusters of tiny red fungal dots on a normally smooth beech trunk [1][3]
3. Crown dieback, or beech trunks that have snapped off ("beech snap") [1]

What you can do:

1. Do not move beech firewood or logs ? buy and burn firewood locally, since moving infested wood is the main way the disease makes long jumps to new areas [1].
2. Avoid wounding beech bark (from string trimmers, nails, or careless pruning), because fresh wounds give the fungus another way in [1][3].
3. If you have a heavily diseased beech that threatens a house, walkway, or play area, have it removed before it snaps or drops limbs [1].
4. Watch for and protect any healthy, smooth-barked beech that stay free of the white scale ? a small share of trees are naturally resistant and are worth keeping [3].
5. Land managers and crews should monitor the leading edge of the infestation, retain and favor resistant scale-free beech, and manage hazard trees along trails and roads, rather than clearing all beech [3].

When to call a professional:

1. Large, valued, or hazardous beech trees, or trees near buildings ? have a certified arborist or forester assess and, if needed, remove them [1].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA National Invasive Species Information Center. Beech Bark Disease. invasivespeciesinfo.gov
2. University of Maryland Extension. Beech Bark Disease. extension.umd.edu
3. Maine Forest Service, Department of Agriculture, Conservation & Forestry. Beech Bark Disease (Cryptococcus fagisuga and Neonectria spp.). maine.gov

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