Beech Bark Disease
Encyclopedia
Beech bark disease is a disease
that causes mortality and defects in beech
trees in the eastern United States
and Europe
. In North America
, the disease results when the beech scale insect
, Cryptococcus fagisuga
, attacks the bark, creating a wound. Later, two different fungi (Nectria
coccinea var. faginata and Nectria galligena) common to North America can invade the tree through the wound, causing a canker
to form. In subsequent years, new cankers will continue to form, ultimately leading to the death of the tree. In Europe, N. coccinea is the primary fungus causing the infection. 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.
Beech bark disease was first documented in Europe in 1849. At first, it was believed that the insect was the main cause of the disease. It wasn’t until 1914 that the fungus was associated with the disease. The first outbreak of beech bark disease in North America appeared in American Beech
(Fagus grandifolia) in Nova Scotia
around 1920. The disease then started to spread to the south and west. In 1929, the first case of beech bark disease was found in the United States in Massachusetts
. By 2004, the disease had spread as far west as Michigan and as far south as western North Carolina
.
The beech scale insect can be observed on the trunk and limbs of the tree as woolly, white tufts that will later develop into broad strips. The woolly, white tufts and broad strips are the colonies of the beech scale insect that are formed in the tiny crevices along the bark. An adult beech scale insect has a soft body, is yellow in color, ranges from 0.5 to 1.0 millimeter long, and has an elliptical shape. The beech scale insect also has a stylet
that it uses to penetrate the bark of the tree for feeding purposes. There are no male beech scale insects and the female insects reproduce parthenogenetically. In mid to late summer, the beech scale insect lays its eggs and dies. The eggs are pale yellow and are laid on the bark in strings of four to eight eggs. The first-stage nymphs (also known as crawlers) begin to hatch in late summer and continue until early winter. They have short antennae
and legs, and move around until they find a suitable and safe place to settle down and force their stylet into the bark and begin feeding. At this point, they begin to secrete the woolly wax cover that they use for protection. This is the second stage of their life cycle and when the spring season comes around they molt again and become adult females.
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.
Symptoms of beech bark disease can be observed in the foliage and on the bole
of the tree. Symptoms affecting the foliage are yellowing, becoming small and sparse, and remaining on the tree during the summer time. Trees that display a thin, weak crown
may persist for several years but may also die without displaying any symptoms. Symptoms that are noticeable on the bole are the cracking of the bark, the formation of cankers, and beech snap. Beech snap is a result of the fungi and insect weakening the wood, which makes it susceptible to being blown over by wind.
conditions, are primarily used on high-value ornamental trees. The use of other organisms as controls is also a possibility. The ladybird beetle is a beetle that preys on the beech scale insect. A fungus that 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 is the best way to reduce the losses of beech in a forest.
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
that causes mortality and defects in beech
Beech
Beech is a genus of ten species of deciduous trees in the family Fagaceae, native to temperate Europe, Asia and North America.-Habit:...
trees in the eastern United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. In North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, the disease results when the beech scale insect
Scale insect
The scale insects are small insects of the order Hemiptera, generally classified as the superfamily Coccoidea. There are about 8,000 species of scale insects.-Ecology:...
, Cryptococcus fagisuga
Cryptococcus fagisuga
Cryptococcus fagisuga, commonly known as the beech scale or woolly beech scale, is a felted scale insect in the superfamily Coccoidea that infests beech trees of the genus Fagus...
, attacks the bark, creating a wound. Later, two different fungi (Nectria
Nectria
This article is about a genus of fungi. For the echinoderm genus, see Nectria .Nectria is a genus of Ascomycete fungi. They are most often encountered as saprophytes on decaying wood but some species can also occur as parasites of trees, especially fruit trees and a number of other hardwood trees...
coccinea var. faginata and Nectria galligena) common to North America can invade the tree through the wound, causing a canker
Canker
Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately...
to form. In subsequent years, new cankers will continue to form, ultimately leading to the death of the tree. In Europe, N. coccinea is the primary fungus causing the infection. 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.
History and Distribution
American Beech
Fagus grandifolia, also known as American Beech or North american beech, is a species of beech native to eastern North America, from Nova Scotia west to southern Ontario in southeastern Canada, west to Wisconsin and south to eastern Texas and northern Florida in the United States. Trees in the...
(Fagus grandifolia) in Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
around 1920. The disease then started to spread to the south and west. In 1929, the first case of beech bark disease was found in the United States in Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
. By 2004, the disease had spread as far west as Michigan and as far south as western North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
.
The Destructive Duo
In order for beech bark disease to occur, two components are required, an insect and a fungus.The Insect
Stylet
A stylet is a hard, sharp, anatomical structure found in some invertebrates.For example, the word stylet or stomatostyle, is used for the primitive piercing mouthparts of some nematodes and some nemerteans...
that it uses to penetrate the bark of the tree for feeding purposes. There are no male beech scale insects and the female insects reproduce parthenogenetically. In mid to late summer, the beech scale insect lays its eggs and dies. The eggs are pale yellow and are laid on the bark in strings of four to eight eggs. The first-stage nymphs (also known as crawlers) begin to hatch in late summer and continue until early winter. They have short antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
and legs, and move around until they find a suitable and safe place to settle down and force their stylet into the bark and begin feeding. At this point, they begin to secrete the woolly wax cover that they use for protection. This is the second stage of their life cycle and when the spring season comes around they molt again and become adult females.
The Fungus
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. These fungi infect the tree through the wounds caused by the beech scale insect and then begin to produce spores. One type of spore that is produced is perithecia. Perithecia 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. Even though the perithecia occur on dead bark, they still have the ability to produce viable spores the next year.Signs and Symptoms
The first sign that is visible is a woolly, white, waxy covering that the beech scale insect secretes. This sign can be observed covering small areas or most of the tree. The amount of waxy material observed depends on the populationPopulation
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
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.
Symptoms of beech bark disease can be observed in the foliage and on the bole
Bole
-Geographical locations:* Bole District, Ghana* Bole, Ghana, town* Bole, Nottinghamshire, England* Bole International Airport * Bole, Xinjiang, China-Other:* Bole2Harlem, an Ethiopian hip hop fusion band* Bole , a unit of momentum...
of the tree. Symptoms affecting the foliage are yellowing, becoming small and sparse, and remaining on the tree during the summer time. Trees that display a thin, weak crown
Crown (botany)
The crown of a plant refers to the totality of the plant's aboveground parts, including stems, leaves, and reproductive structures. A plant canopy consists of one or more plant crowns growing in a given area....
may persist for several years but may also die without displaying any symptoms. Symptoms that are noticeable on the bole are the cracking of the bark, the formation of cankers, and beech snap. Beech snap is a result of the fungi and insect weakening the wood, which makes it susceptible to being blown over by wind.
Controls
There are a few controls for beech bark disease. One important control is the prohibition of movement of nursery stock or other materials that may harbor the beech scale insect.Insecticides, generally not applied under forestForest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
conditions, are primarily used on high-value ornamental trees. The use of other organisms as controls is also a possibility. The ladybird beetle is a beetle that preys on the beech scale insect. A fungus that 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 is the best way to reduce the losses of beech in a forest.