Beech bark disease

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Beech bark disease
Perithecia (Fruiting bodies)
Causal agentsNeonectria faginata and Neonectria ditissima
Hostsbeech trees
VectorsCryptococcus fagisuga
EPPO CodeNNECSP
DistributionEastern United States and Europe

Beech bark disease is a disease that causes mortality and defects in beech trees in the eastern United States, Canada and Europe.[1][2][3] In North America, the disease occurs after extensive bark invasion by Xylococculus betulae and the beech scale insect, Cryptococcus fagisuga.[4] Through a presently unknown mechanism, excessive feeding by this insect causes two different fungi (Neonectria faginata (previously Nectria coccinea var. faginata) and Neonectria ditissima (previously Nectria galligena)) to produce annual cankers on the bark of the tree. The continuous formation of lesions around the tree eventually girdles it, resulting in canopy death. In Europe, N. coccinea is the primary fungus causing the infection.[3] Infection in European trees occurs in the same manner as it does in North American trees. Though the disease still appears in Europe, it is less serious today than it once was.[2]

History and distribution

Distribution map of American Beech and the beech scale insect.

In Europe, beech bark disease was first documented in 1849, while the first North American observation of Cryptococcus fagisuga occurred in 1890 and the first North American observation of Neonectria dates to approximately 1900.

American Beech (Fagus grandifolia) in Nova Scotia around 1920. The disease then started to spread to the south and west. The first case of beech bark disease in the United States was reported in 1929 in Massachusetts. By 2004, the disease had spread as far west as Michigan and as far south as western North Carolina.[2][3]

Mechanism of infection

For beech bark disease to occur, two components are required, an insect and a fungus.

Beech scale insect

Mature beech scale insects.
Beech scale nymph.

The beech scale insect, Cryptococcus fagisuga, is invasive to North America and is host-specific, feeding exclusively on beech trees.

molt again and become adult females.[1][3] A second type of scale insect, Xylococcus betulae, which is non-host-specific, is native to North America and causes beech bark disease to a lesser degree than Cryptococcus fagisuga.[5]

Fungi

There are two fungi common to North America that are important to the beech bark disease process. They are Neonectria faginata and Neonectria ditissima. The primary fungus is N. faginata, though N. ditissima is very important in some areas.

spores. Spores are contained in perithecia, which are red, lemon-shaped fruiting bodies that form in clusters on the bark. These perithecia mature in the fall, and once they have become sufficiently moist, they each release eight spores that are carried by the wind to other beech trees.[1][3] Even though the perithecia occur on dead bark, they still have the ability to produce viable spores the next year.[1]

Signs and symptoms

The first visible sign of a beech scale insect infestation is a woolly, white, waxy covering that the insect secretes. This sign can be observed covering small areas or most of the tree. The amount of waxy material observed depends on the population of the beech scale insect on that tree. The Neonectria fungi also show signs of its presence. An early sign is what looks like a bleeding spot on the tree. A reddish-brown fluid will ooze from the wound site, giving it this appearance. Later, perithecia will form around the dead spot, which is another sign of the disease.[1][2]

foliage and on the bole of the tree. Foliage may become small, sparse and yellowed. Trees that display a thin, weak crown may persist for several years but may also die without displaying any symptoms.[2]
Noticeable symptoms on the bole are the cracking of the bark, the formation of cankers, and beech snap, in which the trunk snaps above head height, under stress from wind as a result of the fungi weakening the wood.

Management strategies

There are a few controls for beech bark disease. One important management strategy is prohibiting the movement of

parasitizes the Neonectria fungus could also be employed. The problem with using these organisms to control beech bark disease is that their impact on the disease has not been evaluated extensively. In a forest setting, controlling the beech bark disease is too costly. Timely salvage cutting can reduce economic losses of beech in a forest, however it is preferable to avoid cutting disease-resistant trees.[1][3] In stands where beech bark disease is established, silvicultural best practice is to retain large overstory trees which show visual resistance (no scale, cankers or fungus), remove heavily infested/dying trees and then treat sprouts from infested trees with herbicides. The residual, resistant parent trees are future sources of resistant seed/sprouts.[8][9] If herbicides are not a viable option, cut all suckers within 1.5 m of a BBD-killed beech tree.[10] Resistance to beech bark disease in a stand may be 1–5% of trees or more, with significant regional variation. A study of 35 sites in three Canadian provinces found resistance rates ranging from 2.2 to 5.7%.[11]

  • Thin, weak crown with yellow foliage.
    Thin, weak crown with yellow foliage.
  • Beech snap.
    Beech snap.
  • White, waxy secretions.
    White, waxy secretions.
  • Bleeding Spot.
    Bleeding Spot.

See also

References

  1. ^ a b c d e f g h i Houston, David R., and James T. O'Brien. "Beech Bark Disease." Forest Insect and Disease Leaflet 75(1998) 1-7. 17 Mar 2008 <http://www.na.fs.fed.us/spfo/pubs/fidls/beechbark/fidl-beech.htm[permanent dead link]>.
  2. ^ a b c d e f g Tainter, Frank H., and Fred A. Baker . Principles of Forest Pathology. New York, NY: John Wiley & Sons, Inc., 1996.
  3. ^ a b c d e f g Sinclair, Wayne A., and Howard H. Lyon. Diseases of Trees and Shrubs. 2nd ed. Ithaca, NY: Cornell University Press, 2005.
  4. ^
    doi:10.1016/j.foreco.2017.03.031
    .
  5. ^
    doi:10.1016/j.foreco.2014.10.019
    .
  6. ^ a b c d "Beech Bark Disease - FIDL". www.na.fs.fed.us. Retrieved 2015-11-23.[permanent dead link]
  7. ^ Beech Bark Disease Best Management Practices for Reducing the Movement of the Beech Scale
  8. ^ Silvicultural Options for Restoration of American Beech Resistant to Beech Bark Disease
  9. ^ Beech Party: How to Promote Beech (yes, promote) on Your Woodlot
  10. ^ SURVIVAL OF THE FITTEST:BEECH BARK DISEASE-RESISTANT BEECH WILL LEAVE MORE OFFSPRING
  11. ^ Incidence of beech bark disease resistance in the eastern Acadian forest of North America

External links

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