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Common name
felted beech coccus (English), woolly beech scale insect (English), felted beech scale (English), beech scale insect (English), beech scale (English), woolly beech scale (English)
Synonym
Cryptococcus fagi , Baer.
Similar species
Summary
The beech scale insect (Cryptococcus fagisuga), along with Neonectria ascomycete fungi form the disease-complex responsible for beech bark disease (BBD) of American and European beech. Beech scale infests mainly larger sized beech trees, feeding on host tissues and causing small fissures on the bark. This initial damage to the tree allows Neonectria to enter the tree, which kills host tissue and eventually girdles the tree causing it to die. In North America the main fungi involved are N. faginata and N. ditissima, whereas in Europe N. ditissima and N. coccinea are responsible for the disease. BBD can dramatically alter forest stand composition and structure, through loss of large trees and proliferation of smaller trees that originate from root sprouting. Reduction of beech nut production and loss of large trees in infected stands may affect mammals and birds that use beech nuts as important food source and old trees as habitat. Around 1% of American beech is estimated to be resistant to BBD. Research is currently focused on modes of inheritance and propagation methods.
Species Description
Beech scales (Cryptococcus fagisuga) are yellow, soft bodied scale insects measuring 0.5 to 1.0 mm long as adults. Female adults (no males of this species are known) are legless, wingless and have only rudimentary antennae. They attach to trees only by their 2 mm long stylets. Nymphs possess glands that secrete a white, woolly wax that covers their bodies (McCullough et al., 2003), and causes heavily infested trees to heavily appear as though they are covered by white wool (McCullough et al., 2003). Unlike some scale insects C. fagisuga has no filament (Kosztarab, 1996 in Wiggins et al., 2004).
Lifecycle Stages
Cryptococcus fagisuga has one generation per year. Adults lay pale yellow eggs on the bark of beech trees in midsummer (June to September) before they die. Eggs are attached end to end in strings of four to seven eggs. First instar, mobile crawlers hatch from eggs 25 days later in late summer to early winter. These immature scales are unlike adults in having legs and functional antennae. They are able to move about in order to find a suitable location. Once located they force their long, tube-like stylet into the bark to suck the sap. Once a nymph has begun to feed it moults to the second instar which have no legs and are immobile. They produce the white wax that eventually covers their bodies. Second instars overwinter and moult to the adult stage the following spring (McCullough et al., 2003; Houston, 1994a).
Habitat Description
Cryptococcus fagisuga infects American beech (Fagus gradifolia Ehrh) and European beech (F. sylvatica) trees. Trees around 25 years old appear to be particularly susceptible to attack (Wainhouse, 1980), whereas smaller, younger trees (3-10 and 11-17 cm classes) may be a less suitable habitat (Fernandez & Boyer, 1988; Houston, 1988). Larger trees may be more susceptible to scale infestation due to more suitable spatial habitat and more nutritious bark. Larger trees have high nitrogen concentration, which is known to influence scale insect growth and development. Greater scale fecundity on larger trees yields higher infestation and, greater fungal infection and more severe disease development (Latty et al., 2003).

Nymphs prefer to colonise areas of the tree where the bark is rough. Infestations often start near old branch stubs, under large branches or sometimes beneath moss or lichens (Houston, 1979; McCullough et al., 2003). The ability of the beech scale to establish itself of individual trees varies widely and is influenced by host resistance, bark epiphytes and possibly by predators and pathogens (Houston, 1994a). The beech scale prefers moist and shaded habitats (Gavin & Peart, 1993), although high rainfall is thought to be detrimental to scale populations and BBD as it may wash crawlers from trees and affect Neonectria spore production and dissemination (Houston, 1988).
Cold temperatures reduce the overwintering second-instar scale populations in the winter. Thus heavy rainfall and cold temperatures reduce scale infestation, and hence infection levels of Neonectria and subsequent cankering of trees (Houston, 1988).There appears to be a direct connection between climate and beech scale insect populations. In northern latitudes beech scale is limited by low winter temperature; minimum daily temperatures of -34 °C or below correlate with scale population dieback (Houston & Valentine, 1988 in Dukes et al., 2009).

Neonectria appear to only be limited geographically by the current distribution of beech scale, suggesting that they are not constrained by climate. In fact, perithecium production may be highest in winter as host dormancy reduces the capacity of trees to resist infection (Gove & Houston, 1996 in Dukes et al., 2009). The effect of future climate change scenarios of disease dynamics is unknown, but increased CO2 may enhance tree growth and thus increase susceptibility. Alternatively, increases in CO2 tend to decrease tissue nitrogen concentration, possibly decreasing bark nitrogen and thus susceptibility to scale attack. Increases in the frequency and severity of storms may influence the longevity of infected trees which are highly vulnerable to windthrow (Dukes et al., 2009).

Reproduction
Scale insects reproduce asexually by parthenogenesis. Thus all beech scales are females and no mating occurs. This form of reproduction allows the insects to rapidly build populations when suitable hosts are present (McCullough et al., 2003).
Nutrition
Cryptococcus fagisuga feeds on American (Fagus grandifolia) and European beech (F. sylvatica). This insect initiates feeding by inserting its long stylet through the bark tissue and into the cortex and phloem to feed on the vascular fluid of trees (Ehrlich, 1934 in Wiggins et al., 2004).

Acquisition of nitrogen is important for scale insects, and affects their growth and development. Larger trees are more susceptible to scale infestation in part because they have higher nitrogen levels, and thus more nutritious bark. Similarly, old growth forests generally have higher than secondary growth forests, and are thus more susceptible to beech scale infestation and BBD (Latty et al., 2003).

Pathway
Beech scale has may be transported on beech specimens shipped by plant collectors (Gwiazdowski et al., 2006). Beech scale is thought to have been introduced to Canada from Europe in an infested beech shipment (McCullough et al., 2003). Beech scale infestations in Michigan, West Virginia and Ohio are all centered on campgrounds or scenic areas, suggesting that humans likely play a role in moving scales long distances, e.g. by moving firewood.

Principal source:

Compiler: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)

Review:

Publication date: 2011-03-23

Recommended citation: Global Invasive Species Database (2017) Species profile: Cryptococcus fagisuga. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=1695 on 18-11-2017.

General Impacts
Beech bark disease (BBD) is caused by the combined impacts of beech scale insect (Cryptococcus fagisuga) and several species of ascomycete fungi in the genus Neonectria. BBD affects American (Fagus grandifolia) and European beech (F. sylvatica). Two principal species of Neonectria fungi are associated with BBD in North America. The probably introduced Neonectria faginata only infects F. grandifolia and is the main species involved with the disease. Native N. ditissima (N. galligena) affects a range of tree species, including beech (Houston, 1994a). In many cases N. faginata spreads to stands infected with N. ditissima and replaces this species as the dominant pathogen (Houston, 1994b; Kasson et al., 2009). A third species N. ochroleuca (now named Bionectria ochroleuca) has been found in association with BBD in some regions of the United States (Houston, 2005). In Europe the fungi associated with BBD are N. ditissima and N. coccinea (Twery & Patterson, 1984; Castlebury et al., 2006).

The beech scale insect feeds on host parenchyma cells which collapse and die, resulting in small fissures on the bark that allow Neonectria to enter the tree. Heavy infestations of scale allow Neonectria to spread rapidly within the bark (Houston, 1994a). As the fungal mycelia grow, large areas of tissues become weakened and die, sometimes causing cankers on the trunk and branches. Sometimes red-brown liquid oozes from the bark tissues killed by the fungi, and the foliage of severely affected trees may become sparse and turn yellow (LeGuerrier et al., 2003). If enough tissue is killed the tree will be girdled and die (Koch et al., 2010). The course of the disease may take as little as two years, but other trees may linger for several years.

Much research has suggested that BBD mainly affects large, older trees, and may cause up to 80% mortality of beech within a stand (Houston, 1994a). Death of older trees leads to gradual gaps in the canopy. This gives the opportunity for other tree species to take over, sometimes leading to drastic changes in the composition and structure of stands (Twery & Patterson, 1984; Runkle, 1990; Wiggins et al., 2004). Particularly in stands dominated by BBD-tolerant species such as eastern hemlock (Tsuga canadensis) and sugar maple (Acer saccharum); these species dominate and American beech may become a minor component of the stand (Twery & Patterson, 1984).

However in most forest stands BBD favours the development of dense beech thickets that interfere with the regeneration of other trees (Houston, 1994a; Garnas et al., 2011), due to beech’s propensity to reproduce vegetatively via adventitious root sprouts, especially from damaged root sprouts (Garnas et al., 2011). Thus in many forests there is actually an increase in beech volume accumulation, particularly 10-20 years after BBD invasion (Morin et al., 2007).

Beech is a highly important tree for many birds and mammals due to the habitat large old trees provide and for the beechnuts produced during mast years. Loss of larger trees may reduce food and habitat and have negative impacts for animals, which may ramify through the ecosystem (Lovett et al., 2006; Wiggins et al., 2004).

Diseased trees are more prone to “beech snap” during high wind events. This poses a threat to people and personal property where trees occur in campgrounds, recreation areas or near homes (McCullough et al., 2003; Heyd, 2005). Alteration to beech composition may also have economic impacts, both negative and positive (Garnas et al., 2011).

For a detailed account of the impacts of beech bark disease please read Impacts of Beech Bark Disease

Management Info
Most control methods focus on reducing populations of the beech scale, as Neonectria are unable to colonise trees that have not been previously infested with the scale. Thus control of Cryptococcus fagisuga is likely to slow the spread of BBD (Wiggins et al., 2004).

Cultural: Thinning and removal of infected or susceptible trees, while retaining resistant trees is a commonly used management strategy. This is important for decreasing long-term susceptibility and vulnerability of forests to beech bark disease. Potentially resistant trees can be identified by smooth bark and vigour. In contrast, large overmature trees, trees with rough bark, and trees with wounds, broken tops or other obvious problems are most likely to be infested by beech scale and most vulnerable to Neonectria infection (McCullough et al., 2003). However such practices not feasible in large areas of natural forest due to labour, financial and practical constraints (Wiggins et al., 2004).

Physical: Physical removal of scale insects by scrubbing trees, high pressure water, or use of petroleum-based oils, which cover and suffocate scale insects may be used on individual high-value ornamental or yard trees (McCullough et al., 2003).

Chemical: There is no practical chemical control for beech scale (Pond, 2008), although insecticides may be used for individual high-value ornamental or yard trees (McCullough et al., 2003). Herbicides may be used in some cases to control beech regeneration, in order to minimise root sprouting and the creation of dense beech thickets (McCullough et al., 2003). Pesticides are not acceptable control options in large natural areas because of labour, financial, environmental and practical constraints (Wiggins et al., 2004).

Biological: The most desirable option for control of BBD is a biological control agent of C. fagisuga (Wiggins et al., 2004). A number of natural predators and pathogens of C. fagisuga have been identified including coccinellids, mites, gall gnats and a fungus (Shingo, 1964 in Houston, 1994a; Wiggins et al., 2004; Dukes et al., 2009). However none are effective in stopping its spread to date (Pond, 2008), and much further research is required (Wiggins et al., 2004).

Genetic: An estimated 1% of American beech trees are resistant to scale insect infestation, and thus BBD. The cause of resistance to BBD remains unidentified (Koch et al., 2007), although in European beech resistance appears to be due to anatomical features that act as barriers to infestation (Lonsdale, 1983a in Houston, 2005), whereas in American beech resistance may be associated with less total and amino nitrogen concentration (Wargo, 1988 in Houston, 2005). Recent findings suggest that resistance to BBD ranges from partial to total resistance (Ramirez et al., 2007).

Currently the only known method to identify resistant trees is the artificial infestation method developed by Houston (1982). Drawbacks to this method include the minimum 1-year wait for results and the reliance on live scale eggs which could result in spread of the insect. Thus much research is focused on identification of genetic markers for resistance, trials to clarify modes of inheritance via cross-breeding resistant and susceptible individuals, and methods of propagation via somatic embryogenesis (Koch & Carey, 2005; Loo et al. 2005; Pond, 2008).

For a detailed account of management options for beech bark disease please read Management of Beech Bark Disease

Countries (or multi-country features) with distribution records for Cryptococcus fagisuga
NATIVE RANGE
  • asia
  • eastern europe
  • southwestern asia
Informations on Cryptococcus fagisuga has been recorded for the following locations. Click on the name for additional informations.
Lorem Ipsum
Location Status Invasiveness Occurrence Source
Details of Cryptococcus fagisuga in information
Status
Invasiveness
Arrival date
Occurrence
Source
Introduction
Species notes for this location
Location note
Management notes for this location
Impact
Mechanism:
Outcome:
Ecosystem services:
Impact information
Beech bark disease (BBD) is caused by the combined impacts of beech scale insect (Cryptococcus fagisuga) and several species of ascomycete fungi in the genus Neonectria. BBD affects American (Fagus grandifolia) and European beech (F. sylvatica). Two principal species of Neonectria fungi are associated with BBD in North America. The probably introduced Neonectria faginata only infects F. grandifolia and is the main species involved with the disease. Native N. ditissima (N. galligena) affects a range of tree species, including beech (Houston, 1994a). In many cases N. faginata spreads to stands infected with N. ditissima and replaces this species as the dominant pathogen (Houston, 1994b; Kasson et al., 2009). A third species N. ochroleuca (now named Bionectria ochroleuca) has been found in association with BBD in some regions of the United States (Houston, 2005). In Europe the fungi associated with BBD are N. ditissima and N. coccinea (Twery & Patterson, 1984; Castlebury et al., 2006).

The beech scale insect feeds on host parenchyma cells which collapse and die, resulting in small fissures on the bark that allow Neonectria to enter the tree. Heavy infestations of scale allow Neonectria to spread rapidly within the bark (Houston, 1994a). As the fungal mycelia grow, large areas of tissues become weakened and die, sometimes causing cankers on the trunk and branches. Sometimes red-brown liquid oozes from the bark tissues killed by the fungi, and the foliage of severely affected trees may become sparse and turn yellow (LeGuerrier et al., 2003). If enough tissue is killed the tree will be girdled and die (Koch et al., 2010). The course of the disease may take as little as two years, but other trees may linger for several years.

Much research has suggested that BBD mainly affects large, older trees, and may cause up to 80% mortality of beech within a stand (Houston, 1994a). Death of older trees leads to gradual gaps in the canopy. This gives the opportunity for other tree species to take over, sometimes leading to drastic changes in the composition and structure of stands (Twery & Patterson, 1984; Runkle, 1990; Wiggins et al., 2004). Particularly in stands dominated by BBD-tolerant species such as eastern hemlock (Tsuga canadensis) and sugar maple (Acer saccharum); these species dominate and American beech may become a minor component of the stand (Twery & Patterson, 1984).

However in most forest stands BBD favours the development of dense beech thickets that interfere with the regeneration of other trees (Houston, 1994a; Garnas et al., 2011), due to beech’s propensity to reproduce vegetatively via adventitious root sprouts, especially from damaged root sprouts (Garnas et al., 2011). Thus in many forests there is actually an increase in beech volume accumulation, particularly 10-20 years after BBD invasion (Morin et al., 2007).

Beech is a highly important tree for many birds and mammals due to the habitat large old trees provide and for the beechnuts produced during mast years. Loss of larger trees may reduce food and habitat and have negative impacts for animals, which may ramify through the ecosystem (Lovett et al., 2006; Wiggins et al., 2004).

Diseased trees are more prone to “beech snap” during high wind events. This poses a threat to people and personal property where trees occur in campgrounds, recreation areas or near homes (McCullough et al., 2003; Heyd, 2005). Alteration to beech composition may also have economic impacts, both negative and positive (Garnas et al., 2011).

For a detailed account of the impacts of beech bark disease please read Impacts of Beech Bark Disease

Red List assessed species 0:
Mechanism
[1] Competition
[3] Parasitism
Outcomes
[2] Environmental Ecosystem - Habitat
  • [1] Reduction in native biodiversity
  • [1] Modification of successional patterns
[3] Environmental Species - Population
  • [3] Plant/animal health
[1] Socio-Economic
  • [1] Damage to forestry
Management information
Most control methods focus on reducing populations of the beech scale, as Neonectria are unable to colonise trees that have not been previously infested with the scale. Thus control of Cryptococcus fagisuga is likely to slow the spread of BBD (Wiggins et al., 2004).

Cultural: Thinning and removal of infected or susceptible trees, while retaining resistant trees is a commonly used management strategy. This is important for decreasing long-term susceptibility and vulnerability of forests to beech bark disease. Potentially resistant trees can be identified by smooth bark and vigour. In contrast, large overmature trees, trees with rough bark, and trees with wounds, broken tops or other obvious problems are most likely to be infested by beech scale and most vulnerable to Neonectria infection (McCullough et al., 2003). However such practices not feasible in large areas of natural forest due to labour, financial and practical constraints (Wiggins et al., 2004).

Physical: Physical removal of scale insects by scrubbing trees, high pressure water, or use of petroleum-based oils, which cover and suffocate scale insects may be used on individual high-value ornamental or yard trees (McCullough et al., 2003).

Chemical: There is no practical chemical control for beech scale (Pond, 2008), although insecticides may be used for individual high-value ornamental or yard trees (McCullough et al., 2003). Herbicides may be used in some cases to control beech regeneration, in order to minimise root sprouting and the creation of dense beech thickets (McCullough et al., 2003). Pesticides are not acceptable control options in large natural areas because of labour, financial, environmental and practical constraints (Wiggins et al., 2004).

Biological: The most desirable option for control of BBD is a biological control agent of C. fagisuga (Wiggins et al., 2004). A number of natural predators and pathogens of C. fagisuga have been identified including coccinellids, mites, gall gnats and a fungus (Shingo, 1964 in Houston, 1994a; Wiggins et al., 2004; Dukes et al., 2009). However none are effective in stopping its spread to date (Pond, 2008), and much further research is required (Wiggins et al., 2004).

Genetic: An estimated 1% of American beech trees are resistant to scale insect infestation, and thus BBD. The cause of resistance to BBD remains unidentified (Koch et al., 2007), although in European beech resistance appears to be due to anatomical features that act as barriers to infestation (Lonsdale, 1983a in Houston, 2005), whereas in American beech resistance may be associated with less total and amino nitrogen concentration (Wargo, 1988 in Houston, 2005). Recent findings suggest that resistance to BBD ranges from partial to total resistance (Ramirez et al., 2007).

Currently the only known method to identify resistant trees is the artificial infestation method developed by Houston (1982). Drawbacks to this method include the minimum 1-year wait for results and the reliance on live scale eggs which could result in spread of the insect. Thus much research is focused on identification of genetic markers for resistance, trials to clarify modes of inheritance via cross-breeding resistant and susceptible individuals, and methods of propagation via somatic embryogenesis (Koch & Carey, 2005; Loo et al. 2005; Pond, 2008).

For a detailed account of management options for beech bark disease please read Management of Beech Bark Disease

Bibliography
57 references found for Cryptococcus fagisuga

Managment information
Garnas R. Jeffrey, Matthew P. Ayres, Andrew M. Liebhold and Celia Evan, 2011. Subcontinental impacts of an invasive tree disease on forest structure and dynamics. Journal of Ecology 2011, 99, 532�541
Heyd, Robert L. 2005. Managing beech bark disease in Michigan. In: C.A. Evans, J.A. Lucas & Twery, M.J. (Eds) Beech bark disease. Proceedings of the beech bark disease symposium. Saranac Lake, NY, 16�18 June 2004. USDA Forest Service, NE Res Station, Gen Tech Rep NE-331. pp. 128-132.
Koch, Jennifer L. & Carey, David W. 2005. The genetics of resistance of American beech to beech bark disease: knowledge through 2004. In: C.A. Evans, J.A. Lucas & Twery, M.J. (Eds) Beech bark disease. Proceedings of the beech bark disease symposium. Saranac Lake, NY, 16�18 June 2004. USDA Forest Service, NE Res Station, Gen Tech Rep NE-331. pp. 98-105.
Koch, Jennifer L.; Carey, David W.; Mason, Mary E.; Nelson, C. Dana, 2010. Assessment of beech scale resistance in full- and half-sibling American beech families. Canadian Journal of Forest Research. 40(2). FEB 2010. 265-272.
Loo, Judy; Ramirez, M. & Krasowski, M. 2005. American beech vegetative propagation and genetic diversity. In: C.A. Evans, J.A. Lucas & Twery, M.J. (Eds) Beech bark disease. Proceedings of the beech bark disease symposium. Saranac Lake, NY, 16�18 June 2004. USDA Forest Service, NE Res Station, Gen Tech Rep NE-331. pp. 106-112.
Morris, Ashley B.; Small, Randall L.; Cruzan, Mitchell B., 2002. Investigating the relationship between Cryptococcus fagisuga and Fagus grandifolia in Great Smoky Mountains National Park. Southeastern Naturalist. 1(4). 2002. 415-424.
Pond, Sharon E. 2008. Conservation and propagation of American beech (Fagus grandifolia ehrh.) through somatic embryogenesis. Propagation of Ornamental Plants. 8(2). 2008. 81-86.
Wainhouse D. 1980. Dispersal of First Instar Larvae of the Felted Beech Scale, Cryptococcus fagisuga. Journal of Applied Ecology, Vol. 17, No. 3 (Dec., 1980), pp. 523-532
Wiggins, Gregory J.; Grant, Jerome F.; Welbourn, W. Cal, 2001. Allothrombium mitchelli (Acari: Trombidiidae) in the Great Smoky Mountains National Park: Incidence, seasonality, and predation on beech scale (Homoptera: Eriococcidae). Annals of the Entomological Society of America. 94(6). November, 2001. 896-901.
General information
Beachy, Brian L. & Storer, Andrew J. Wood-infesting insect abundance and community structure in relation to beech bark disease. 2005. In: C.A. Evans, J.A. Lucas & Twery, M.J. (Eds) Beech bark disease. Proceedings of the beech bark disease symposium. Saranac Lake, NY, 16�18 June 2004. USDA Forest Service, NE Res Station, Gen Tech Rep NE-331. pp. 94.
Bisessar S.; Mclaughlin D. L.; Linzon, 1985. The 1st occurrence of the beech scale insect Cryptococcus fagisuga on American beech Fagus grandifolia trees in Ontario, Canada. Journal of Arboriculture. 11(1). 1985. 13-14.
Castlebury, Lisa A.; Rossman, Amy Y.; Hyten, Aimee S., 2006. Phylogenetic relationships of Neonectria/Cylindrocarpon on Fagus in North America. Canadian Journal of Botany. 84(9). SEP 2006. 1417-1433.
Covassi M., 1975. New records on the chorology of Cryptococcus fagisuga, new record in Italy and Corsica, France [Homoptera Cryptococcidae] Redia. 56 1975. 555-564.
Summary: Several localities of the Italian Alps and the Apennines where the woolly beech scale C. fagisuga was found are listed. The discovery of this scale in Corsica [France] and also in Sicily is reported for the first time on M. Etna C. fagisuga reaches its European southern limit together with its host plants.
Dukes, Jeffrey S.; Pontius, Jennifer; Orwig, David; Garnas, Jeffrey R.; Rodgers, Vikki L.; Brazee, Nicholas; Cooke, Barry; Theoharides, Kathleen A.; Stange, Erik E.; Harrington, Robin; Ehrenfeld, Joan; Gurevitch, Jessica; Lerdau, Manuel; Stinson, Kristina ; Wick, Robert; Ayres, Matthew, 2009. Responses of insect pests, pathogens, and invasive plant species to climate change in the forests of northeastern North America: What can we predict? Canadian Journal of Forest Research. 39(2). FEB 2009. 231-248.
Faison, Edward K.; Houston, David R., 2004. Black bear foraging in response to beech bark disease in northern Vermont. Northeastern Naturalist. 11(4). 2004. 387-394.
Fernandez M. R.; Boyer M. G., 1988. Beech bark disease: A survey of the Toronto area Canada. Canadian Plant Disease Survey. 68(2). 1988. 157-160.
Fernandez M. R.; Boyer M. G., 1989. Beech bark mycoflora and its distribution in relation to the presence of the scale insect Cryptococcus fagisuga Lind. Canadian Plant Disease Survey. 69(2). 1989. 101-104.
Forrester, Jodi A.; McGee, Gregory G.; Mitchell, Myron J., 2003. Effects of beech bark disease on aboveground biomass and species composition in a mature northern hardwood forest, 1985 to 2000. Journal of the Torrey Botanical Society. 130(2). April-June 2003. 70-78.
Gavin, David G.; Peart, David R., 1993. Effects of beech bark disease on the growth of American beech (Fagus grandifolia). Canadian Journal of Forest Research. 23(8). 1993. 1566-1575.
Griffin, Jacob M.; Lovett, Gary M.; Arthur, Mary A.; Weathers, Kathleen C., 2003. The distribution and severity of beech bark disease in the Catskill Mountains, N.Y. Canadian Journal of Forest Research. 33(9). September 2003. 1754-1760.
Gwiazdowski, Rodger A.; Van Driesche, Roy G.; Desnoyers, Adrienne; Lyon, Suzanne; Wu, San-An; Kamata, Naotoa; Normark, Benjamin B., 2006. Possible geographic origin of beech scale, Cryptococcus fagisuga (Hemiptera : Eriococcidae), an invasive pest in North America. Biological Control. 39(1). OCT 2006. 9-18.
Hane, Elizabeth N., 2003. Indirect effects of beech bark disease on sugar maple seedling survival. Canadian Journal of Forest Research. 33(5). May 2003. 807-813.
Houston, David R., 1994b. Temporal and spatial shift within the Nectria pathogen complex associated with beech bark disease of Fagus grandifolia. Canadian Journal of Forest Research. 24(5). 1994. 960-968.
Houston, David R. 2005. Beech bark disease: 1934 to 204: what s new since Ehrlich? In: C.A. Evans, J.A. Lucas & Twery, M.J. (Eds) Beech bark disease. Proceedings of the beech bark disease symposium. Saranac Lake, NY, 16�18 June 2004. USDA Forest Service, NE Res Station, Gen Tech Rep NE-331. pp 2-13.
Houston D. R. 1994a. Major New Tree Disease Epidemics: Beech Bark Disease! Annu. Rev. Phytopathol. 1994. 32:75--87
Houston D. R.; Parker E. J.; Lonsdale, 1979. Beech bark disease patterns of spread and development of the initiating agent Cryptococcus fagisuga. Canadian Journal of Forest Research. 9(3). 1979. 336-344.
Houston D. R.; Valentine H. T., 1988. Beech bark disease the temporal pattern of cankering in aftermath forests of Maine USA. Canadian Journal of Forest Research. 18(1). 1988. 38-42.
Jakubas, Walter J.; McLaughlin, Craig R.; Jensen, Paul G. & McNulty, Stacy A. 2005. Alternate year beechnut production and its influence on bear and marten populations. In: C.A. Evans, J.A. Lucas & Twery, M.J. (Eds) Beech bark disease. Proceedings of the beech bark disease symposium. Saranac Lake, NY, 16�18 June 2004. USDA Forest Service, NE Res Station, Gen Tech Rep NE-331. pp. 79-87.
Kasson, Matthew T.; Livingston, William H., 2009. Spatial distribution of Neonectria species associated with beech bark disease in northern Maine. Mycologia. 101(2). MAR-APR 2009. 190-195
Latty, Erika F.; Canham, Charles D.; Marks, Peter L., 2003. Beech bark disease in northern hardwood forests: The importance of nitrogen dynamics and forest history for disease severity. Canadian Journal of Forest Research. 33(2). February 2003. 257-268.
Leak, William B., 2006. Fifty-year impacts of the beech bark disease in the Bartlett Experimental Forest, New Hampshire. Northern Journal of Applied Forestry. 23(2). JUN 2006. 141-143.
Le Guerrier, Catherine; Marceau, Danielle J.; Bouchard, Andre; Brisson, Jacques, 2003. A modelling approach to assess the long-term impact of beech bark disease in northern hardwood forest. Canadian Journal of Forest Research. 33(12). December 2003. 2416-2425.
Loo, Judy A., 2009. Ecological impacts of non-indigenous invasive fungi as forest pathogens. Biological Invasions. 11(1). JAN 2009. 81-96.
Lovett, Gary M.; Canham, Charles D.; Arthur, Mary A.; Weathers, Kathleen C. & Fitzhugh, Ross D. 2006. Forest ecosystem responses to exotic pests and pathogens in Eastern North America. Bioscience 56. MAY 2005. 395-405.
Mackenzie, M.; Iskra, A. J., 2005. The first report of beech bark disease in Ohio comes nineteen years after the first report of the initiating scale. Plant Disease. 89(2). February 2005. 203.
Mahoney, Eileen M.; Milgroom, Michael G.; Sinclair, Wayne A. 1999. Origin, genetic diversity, and population structure of Nectria coccinea var. faginata in North America. Mycologia. 91(4). FEB 1999. 583-592.
McGee, Gregory G., 2000. The contribution of beech bark disease-induced mortality to coarse woody debris loads in northern hardwood stands of Adirondack Park, New York, U.S.A. Canadian Journal of Forest Research. 30(9). September, 2000. 1453-1462.
McLaughlin, C.R.; Matula, G.J.; O�Conner, R.J. 1993. Synchronous reproduction by Maine black bears. International Conference of Bear Research and Management
Mielke M. E.; Haynes C.; Macdonald W. L., 1982. Beech scale and Nectria galligena on beech in the Monongahela Forest West Virginia USA. Plant Disease. 66(9). 1982. 851-852.
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