Invaders TitleNYSM home


A variety of non-native, invasive diseases affect many of our native plants, animals, agricultural crops, and even humans.
These diseases can be caused by microorganisms, including fungi, bacteria, or viruses, that are often “hidden” from sight. This has been an historic as well as current problem. Diseases are typically brought in by accident. They are moved in a variety of ways. They may be in landscaping material, migrating fish or birds, ballast water, insects on aircraft, infected humans, or even movement of firewood. Whatever the means of introduction, the consequences of moving diseases can be devastating.
Plum Pox Virus
Land- und Forstwirtschaft Archive,
Biologische Bundesanstalt für Land- und

Plum Pox Virus

Polyvirus #7 Sharka
Plum Pox Virus is native to Bulgaria. On June 20 and July 7, 2006, the virus was confirmed in two separate orchards in Niagara County. It was first introduced in Pennsylvania on live plant grafts smuggled into the United States by an orchard owner. The virus is spread short distances by aphids and long distances by moving infected nursery stock or plant parts.

Plum Pox Virus affects the “stone fruits” of plum, peaches, apricots, and nectarines. It severely reduces fruit production and causes misshapen and blemished fruits. So far, eradication efforts and rapid response have limited the infestation of Plum Pox Virus to Niagara County.

Mile-a-Minute Weed
Beech Bark Wood
Linda Haugen, USDA Forest Service,

Beech Bark Scales
Scales: insects that feed on beech bark
Joseph O’Brien, USDA Forest Service,

Beech Bark Disease

Felted Beech Scale (Cryptococcus fagisuga)
and associated fungi in the genus Nectria

Beech Bark Disease apparently originates from the Middle East (Turkey and Iran). It arrived in North America around 1890. The disease attacks European Beech, but the most drastic effects have been observed in North America where it attacks American Beech (Fagus grandifolia). This disease consists of two imported agents, an insect and a fungus. The insect is called a scale. The scales feed on the bark phloem (conducting tissue). Their feeding apparently disables wound responses that would otherwise protect damaged bark. The scales are paving the way for the other factor in Beech Bark Disease, pathogenic fungi. Nectria fungi invade the bark, and so begins the slow, steady decline of a previously healthy tree.

Beech Bark Disease Wood Sample

The usually smooth, gray bark of American Beech becomes riddled with cankers from this disease. Large beech trees produce beech nuts that are an important source of food for a variety of wildlife.

Chesnut Blight
Joseph O’Brien, USDA Forest Service,

Chestnut Blight

Cryphonectria parasitica
American Chestnut, at one time our most valuable tree, dominated the eastern forests of the United States before succumbing to Chestnut Blight. An estimated four billion native chestnut trees grew over this range. This disease is caused by a fungus native to eastern Asia.

Cankers caused by the blight were first reported in 1904 in New York City. It was most likely introduced decades earlier on imported Asian chestnut trees. It was spread over the range of our native chestnut trees by “mail order” as people bought non-native chestnut trees from nurseries. The spores of the fungus travel from tree to tree by animals of all kinds. By 1926, the fungus was widespread. Populations of this major forest tree have been decimated throughout its range.
Viral Hemorrhagic Septicemia
Dr. P. Bowser, College of Veterinary
Medicine, Cornell University

Viral Hemorrhagic Septicemia

Novirhabdovirus sp.
Viral Hemorrhagic Septicemia (VHS) is native to Europe, Japan, the Pacific coast from California to Alaska, and the Atlantic coast of North America. It was first documented in the Great Lakes in 2005. It is thought to have been introduced by migrating fish or contaminated ballast water. It was first confirmed in New York waters, in Lake Ontario and the Saint Lawrence River, in May 2006.

VHS is caused by an aquatic rhabdovirus. VHS can be lethal to fish. Almost fifty species of fish are known to be susceptible. Infected fish can display multiple symptoms. In its most acute form, VHS can cause hemorrhaging in the eyes, skin, gills, fin bases, skeletal muscle, and internal organs. Human activities can help spread the virus to other waters. Controlling VHS involves restricting the movement of fish, particularly baitfish, among waters. Anglers are encouraged to keep live wells clean and report a large number of dead or dying fish.