Virginia Invasive Species Council



























Species Profiles

Nine invasive species


A brief overview of nine invasive species follows. It is important to note that these are in no way to be considered the priority species in Virginia, or the species most in need of funding and action; rather, they were selected to describe the breadth of the issues. The following descriptions of nine invasive species, from the well-known pest species kudzu, to the recently emerging invasive species the emerald ash-borer, represent the full range of invasive organisms. Virtually any type of organism, from viruses to mammals, may become an invasive species. Each example illustrates another dimension of the problems posed by invasive species and underscores the need for concerted action to control established invasive species and prevent new organisms from becoming established. All of these species are either found in Virginia or have the potential to become established here.


Kudzu (Pueraria montana) is a well-known invasive plant. Intentionally introduced to the U.S. from its native Japan for use in soil stabilization, kudzu became the "vine that ate the South." Kudzu rapidly grows up and over all other vegetation and creates a dense canopy with its large leaves. It starves other plant species of sunlight and quickly reduces complex natural communities to tangled stands of kudzu. Currently, 7 million acres of land are infested with kudzu. Although used as forage, it produces low yields.

Annual costs to control kudzu by power companies in the Southeast have been estimated at 1.5 million dollars (Britton 2002).

More on kudzu.

Chestnut blight fungus

Less than 100 years ago, the American chestnut was a dominant tree species in the Appalachian Mountains from Maine to Mississippi. It was a valued timber tree and produced a bounty of edible nuts. Chestnut blight fungus (Cryphonectria parasitica) was first noted on trees in New York City in 1904. The blight, introduced from Asia, kills the above-ground part of the chestnut tree. By 1926, the chestnut blight had spread throughout the range of the American chestnut (Anagnostakis 2000). Surviving trees were reduced to shrubby stems that rarely reproduced. The industries that were dependent on American chestnut disappeared.

More on chestnut blight fungus.

Northern snakehead fish

Northern snakehead fish (Channa argus) has become a recent concern in the Mid-Atlantic since being discovered in Maryland ponds and the Potomac River (Courtenay and Williams 2004). A voracious predator with sharp teeth and mature body length of three to four feet, snakeheads have the potential to drastically alter freshwater ecosystems by out-competing native fish species, including many sport fish. Snakeheads prey on fish, frogs, crustaceans and aquatic insects. Many species of snakehead fish, including northern snakehead, have the ability to breath air and crawl short distances between water bodies. Northern snakehead is widely sold as live fish food, even in states where it is illegal to sell. Its native range suggests it could become established throughout the contiguous United States (Courtney and Williams 2004). Snakehead itself may introduce yet another non-native species, a fungal pathogen (Aphanomyces invadans) known as epizootic ulcerative syndrome (EUS). EUS can harm native fish and stock in fish farms (USFWS 2002). All these factors make northern snakehead potentially a very destructive invader.

For current info on northern snakehead fish in Virginia.

Hemlock wooly adelgid

In 1990, one could visit Shenandoah National Park and walk under the huge old eastern hemlock trees of the Limberlost. Spared from timbering before the creation of the park, the stand was true old growth forest. Today, most of the hemlocks at the Limberlost are dead and Virginia's hemlock population is in decline. The ancient giants were brought to their demise by a tiny aphid-like invasive insect, the hemlock wooly adelgid (Adelges tsugae). The adelgid sucks the sap out of hemlock needles and injects toxic saliva. It first appeared in Virginia in 1950, and is native to Asia. There is no effective management strategy currently available, and the adelgid continues to spread throughout the eastern U.S., causing tree mortality and population declines (USFS, no date). Loss of eastern hemlock significantly changes the character of natural communities in Virginia's mountains and may lead to an increase in stream erosion.

For more on hemlock wooly adelgid.


Phragmites (Phragmites australis), is a tall grass species with regional genetic variations found in many parts of the world. At least one variation, or genotype, was introduced into the U.S. and has become an aggressive invader of brackish wetlands in eastern and midwestern states (Saltonstall 2002). Phragmites overwhelms other marsh plant species from above and below with tall stems that may be 15 feet in height and fast growing rhizomes (underground stems) which form new shoots and a thick tangled root mat. By forming tall dense stands with few other plant species, Phragmites creates a habitat that lacks value to wildlife. Once established, it is very difficult and expensive to control (Marks et al. 1993). The Virginia Department of Conservation and Recreation recently mapped over 1200 acres of Phragmites that has invaded wetlands on the seaside and barrier islands of Virginia's Eastern Shore (Myers et al. 2004).

More on phragmites.

West Nile virus

Detected in the U.S. in 1999, West Nile virus is a disease-causing virus that affects birds and mammals, including humans. It was first identified in Uganda in 1937 (Hayes et al. 2005). Since it was discovered in North America, it has spread at an astonishing rate. By 2004, West Nile virus had spread to California, north into Canada, and south into Central America and the Caribbean (Hayes et al. 2005). West Nile virus is transmitted by mosquitoes and can cause West Nile fever (a mild flu-like condition), meningitis, encephalitis or even a polio-like paralysis and death. Since 1999, over 16,000 cases of West Nile virus disease have been reported, with 666 resulting in death. However, most people infected with the virus never get sick, and some experience only mild, flu-like symptoms. West Nile virus also affects many wild and captive bird species, which are the primary means of dispersal (Hayes et al. 2005). Certain species, such as crows and jays, are particularly vulnerable and experience high rates of mortality. Some bird species are better reservoirs of the virus than others. The virus is transmitted from birds to humans by mosquitoes. Recent research also suggests it may be transmitted by blood transfusion, organ transplants, and breast milk (Hayes et al. 2005). The most likely pathway for the virus into the U.S. is via birds in zoos, or commercial and pet trade, although this has not been proven. There are many different possible pathways by which the virus could have arrived in this country (Hayes et al. 2005; Marra et al. 2004; Rappapole et al. 2000).

More on west nile virus.

Zebra mussel

Zebra mussel (Dreissena polymorpha), a native of Russia, spread in the 19th century to western Europe, and probably arrived in the U.S. in the ballast of a transatlantic ship. It was first identified in 1988 in Michigan's Lake St. Claire, which connects Lake Huron and Lake Erie. Less than 10 years later, zebra mussel was found in all five Great Lakes and the Mississippi, Tennessee, Hudson and Ohio River basins. Adult zebra mussels grow to two inches in length and form dense colonies of as many as one million individuals per square meter (USGS 2000). Colonies form on any hard surface, whether living or inanimate. Boats, pipes, piers, docks, plants, clams and even other Zebra mussels serve as viable substrate for this species. Zebra mussel proliferation in U.S. water has had negative economic and ecological impacts. The U.S. Fish and Wildlife Service has estimated a $5 billion economic impact over a 10-year period. Costs are associated with activities such as cleaning and maintenance of water intake pipes, removal of shell build-up on recreational beaches, and control efforts (USGS 2000). Zebra mussel has been discovered in one quarry pond in northern Virginia in 2003. VDGIF is leading control efforts.

More on zebra mussel.

Sudden Oak Death

Phytophthora ramorum, a fungal pathogen of unknown origin (Cave et al. 2005), causes damage to trees and shrubs. It is responsible for "sudden oak death" in California and Oregon, killing tanoak (Lithocarpus densiflorus), coast live oak (Quercus agrifolia), and Californian black oak (Q. kellogii). The fungus causes a wide range of symptoms on oak and rhododendron species, including many horticultural species. It has been detected in an ever-increasing number of nurseries in the U.S. and Europe (Cave et al. 2005), but so far has not been found in native forests in the eastern U.S. Nevertheless, P. ramorum remains a very high concern for foresters and the nursery industry. Many believe it is just a matter of time before it is found in high risk areas of Virginia and other states where known host plant species are widespread and climate conditions are favorable to its growth and dispersal (COMTF 2004; Cave et al. 2005). The only control methods known at this time are quarantine or burning host plants.

More on sudden oak death.

Emerald ash borer

Emerald ash borer (Agrilus planipennis) is a small beetle discovered in Michigan in 2002. A native of China, Korea, Taiwan and Japan, its larvae have killed eight to 10 million ash trees (Fraxinus spp.) in Michigan, Ohio and Indiana ( 2005). Evidence suggests the beetle has been established in Michigan for as long as six to 10 years (USFS 2004). Michigan, Ohio and Indiana state agencies and the U.S. Forest Service are conducting coordinated programs of research, eradication by means of tree removal, and quarantines to prevent further infestations. Several occurrences of emerald ash borer have been discovered in Maryland, all associated with ornamental trees originating from one nursery. This same nursery sold 16 infested ash trees to Fairfax County Public Schools in Virginia. The infested trees and all ash trees within one-half mile radius were removed and incinerated by Fairfax County Forest Pest Section and the Virginia Department of Agriculture and Consumer Services. Monitoring for emerald ash borer in Virginia continues (Fairfax County 2005).


Anagnostakis, S. L. 2001. Revitalization of the majestic chestnut: chestnut blight disease. APSnet website. Available at [Accessed 1 August 2005].

Cave, G.L. B Randall-Schedel, and S.C. Redlin. Risk analysis for Phytophthora ramorum Werres, de Cock and In't Veld, causal agent of Phytophthora canker (sudden oak death), ramorum leaf blight, and ramorum dieback. United States Geologic Survey Animal and Plant Inspection Service, Plant Protection and Quarantine, Center for Plant Health Science and Technology, Raleigh, NC.

[COMTF] California Oak Mortality Task Force. 2004. Phytophthora ramorum: a review of North American and European activity. Available at [Accessed 2 August 2005].

Courtenay, W.R., and J.D. Williams. 2004. Snakehead (Pisces, Channidae): A biological synopsis and risk assessment. U.S.G.S. Circular 1251. 151 pp.

Fairfax County. 2005. Emerald ash borer. Fairfax County website. Available at [Accessed 19 August 2005].

Hayes, E.B., N. Komar, R. S. Nasci, S.P. Montgomery, D. R. O'Leary, and G.L. Campbell. 2005. Epidemiology and transmission dynamics of West Nile virus disease. Emerging Infectious Diseases 11:8 1167-1173.

Marks, M., B. Lapin, J. Randall. 1993. Element stewardship abstract for Phragmites australis, common reed. The Nature Conservancy. Available at [Accessed 29 November 2000].

Marra, P.P., S. Griffing, C. Caffrey, A.M. Kilpatrick, R. McLean, C. Brand, E. Saito, A.P. Dupuis, L. Kramer, and R. Novak. 2004. West Nile virus and wildlife. BioScience 54:5 393-402.

Myers, R.K., K.E. Heffernan, J.T. Weber, and D.R. Young. 2004. Mapping and monitoring of Phragmites on the seaside of Virginia's Eastern Shore. Virginia Department of Conservation and Recreation, Division of Natural Heritage, Richmond, Virginia. Natural Heritage Technical Report #04-15. 29 pp. plus appended map atlas.

Rappole, J.H., S.R. Derrickson, and Z. Hubalek. 2000. Migratory birds and the spread of West Nile virus in the Western Hemisphere. Emerging Infectious Diseases 6:4 319-328.

Saltonstall, K. 2002. Cryptic invasion by a non-native genotype of the common reed, Phragmites australis, into North America. PNAS 99:4 2445-2449.

[USFS] U.S. Forest Service. No date. An exotic pest threat to Eastern hemlock: an initiative for management of hemlock woolly adelgid. USDA Forest Service Forest Health Protection website. Available at (offsite PDF) [Accessed 1 August 2005].

[USGS] United States Geologic Survey. 2000. Zebra mussels cause economic and ecological problems in the Great Lakes. USGS Great Lakes Science Center website. Available at (offsite PDF) [Accessed 3 August 2005]. 2005. A collaborative website administered by Michigan State University with support from the USDA Forest Servcies and Michigan Department of Agriculture. [Accessed 19 August 2005]