They are atop everyone’s list of the most destructive plants to Kentucky’s ecological integrity.
These noxious, invasive exotics out-compete native plants, threaten biodiversity, and in some cases pose a health risk to livestock and humans.
The battle to rid the state of these exotic pest plants rages on each Spring on public and private lands and highway right-of-ways.
In accordance with KRS 176.051, the Kentucky Department of Highways (Kentucky Transportation Cabinet) targets some of these species with a roadside spraying program to prevent their growth from interfering with a driver’s line of sight. Additionally, these plants smother roadside turf grass, can damage pavement, embankments, and clog ditches, causing drainage problems.
In no particular order, here’s the dirty dozen:
Kudzu smothers out beneficial plants, blanketing the ground and trees with a dense canopy of leaves and vines, through which little light can penetrate
• Kudzu (Pueraria montana) is a climbing, deciduous vine capable of reaching lengths of over 100 feet in a single season.
Its fleshy tap roots can reach 7 inches in width and grow nine feet deep, which is one of the reasons the plant is so difficult to eradicate.
A native of Asia, it was first introduced into the U.S. in 1876 at the Philadelphia Centennial Exposition. It was widely planted throughout the eastern United States in an attempt to control erosion.
Its leaves are alternate, compound, and hairy underneath, up to 5.4 inches long. Flowering occurs in midsummer, and long, purple, flowers hang, in clusters, in the axils of the leaves. The fruit is a three-inch long pod, containing up to 10 hard seeds.
Kudzu smothers out beneficial plants, blanketing the ground and trees with a dense canopy of leaves and vines, through which little light can penetrate.
All parts of Poison Hemlock are toxic to livestock and humans, due to high potency of the alkaloid coniine. The ingestion of a small amount of leaves or seeds can easily result in respiratory collapse or renal failure, and death.
• Poison Hemlock (Conium maculatum), as the name implies, is a highly toxic herbaceous plant in the carrot family, Apiaceae.
Native to Europe and North Africa, the hardy plant is capable of living in a variety of environments. It is often found on poorly drained soils, particularly near streams, ditches, and other surface water. It thrives on roadsides and the edges of cultivated fields.
Poison Hemlock can grow five to eight feet tall, with a smooth, green, hollow stem, usually spotted or streaked with red or purple on the lower half of the stem. Seed heads form in late summer.
All parts of the plant are poisonous to livestock and humans, due to the high potency of the alkaloid coniine. The ingestion of a small number of leaves or seeds can easily result in respiratory collapse or renal failure, and death.
• Multiflora Rose (Rosa multiflora) is a species of rose native to China, Japan and Korea.
The shrub climbs over other plants to a height of more than 15 feet. There are two varieties, with white and pink flowers.
This ornamental plant is considered an invasive species though it was originally introduced from Asia as a soil conservation measure, as a natural hedge to border grazing land, and to attract wildlife. It invades a large number of habitats, from hillside pastures and fence rows, to highway rights-of-ways.
The removal of Multiflora Rose requires an aggressive full removal of the plant and its root structure.
• Purple Loosestrife (Lythrum salicaria) is a herbaceous perennial that can grow up to five feet tall and forms colonies, with numerous erect stems growing from a single woody root mass.
The stems are reddish-purple or red to purple and square in cross-section. The flowers are reddish purple, with six petals.
Native to Europe, Asia, northwest Africa, and southeastern Australia, purple loosestrife has been introduced into North America with devastating consequences for wetlands.
Infestations result in a dramatic disruption in water flow and a sharp decline in biological diversity, by altering the biogeochemical and hydrological processes in wetlands, excluding beneficial plants needed by migratory waterfowl.
A single plant may produce up to 2.7 million tiny seeds annually. Easily carried by wind and water, the seeds germinate in moist soils after overwintering.
Once established, stands of Purple Loosestrife can become vast, and are difficult and costly to remove by mechanical and chemical means.
Garlic Mustard is classified as an invasive species in North America, and is one of a few invasive herbaceous species able to completely dominate the understory of forests
• Garlic Mustard (Alliaria petiolata) is a biennial flowering plant that invades forests through a disturbance such as a tree falling, road or trail construction. Prolific seed production allows it to quickly dominate the ground cover.
Native to Europe, Asia, and northwestern Africa, early European settlers brought the herb to North America to use as a garlic type flavoring on fish and other dishes.
Garlic Mustard is a good source of vitamins A and C, and its traditional medicinal purposes include use as a diuretic.
Its second year, the plant flowers, producing cross-shaped white flowers in dense clusters. When blooming is complete, plants produce upright fruits that release seeds in mid-summer.
Garlic Mustard is classified as an invasive species in North America and is one of a few invasive herbaceous species able to completely dominate the understory of forests.
• The Canada Thistle (Cirsium arvense) and Nodding Thistle (Carduus nutans) are perennial plants that grow up to five feet tall. Their roots can grow deep into the ground.
They are very prickly. The male and female plants and their flowers differ.
The plant was thought to have come into the U.S. from Canadian hay.
In the western and northern U.S. thistles present a significant problem in prairie and riparian habitats. In Kentucky, thistles are often found on field edges and roadside ditches.
• With its bright colored berries and fragrant flowers, the Amur Honeysuckle (Lonicera maackii), a variety of Asian Bush Honeysuckle, was imported into the U.S. with good intentions.
It was planted throughout Indiana from the 1950s to 1970s in home and urban landscaping but escaped and is now a major invasive species, present in more than 30 states in the eastern U.S.
This species native to China, Mongolia, Korea and Russia, named for the Amur River, the world’s eighth longest river, which forms the border between Russia and Manchuria.
The deciduous, large shrub can grow up to 15 feet tall, and flowers from mid-spring to early summer.
Its fruit is a bright red to black semi-translucent berry containing numerous small seeds. These high-carbohydrate “treats,” that ripen in autumn, are eaten by birds, which disperse the seeds in their droppings. That’s why bush honeysuckle often grows in fence lines and roadways, especially along interstate highway corridors, where there is good habitat for songbirds.
Bush honeysuckle can form extremely dense thickets in forest understories, shading out, and out-competing native shrubs, young trees, and wildflowers. This species poses a serious threat not only to the diversity of ecosystems that are invaded but to forest regeneration itself.
Eradication is costly and labor-intensive — mechanically ripping the shrubs out of the ground, cutting, or burning the plant to root level. To ensure eradication, stumps that are cut should be treated with herbicides.
• Johnson Grass (Sorghum halepense) is native to the Mediterranean but grows throughout Europe and the Middle East.
The grass has been introduced to all continents except Antarctica. It reproduces by rhizomes and seeds.
Johnson Grass was introduced for forages and to stop erosion, but it has become a problem. If wilted from frost or hot, dry weather, the grass can contain amounts of hydrogen cyanide, which can kill cattle and horses if it is eaten in quantity. Also, cattle that eat Johnson Grass can “bloat” from the accumulation of nitrates.
It grows and spreads quickly, and is found in crop fields, pastures, abandoned fields, rights-of-way, forest edges, and along stream banks.
Johnson Grass is considered to be one of the ten worst weeds in the world.
It is named after an Alabama plantation owner, Colonel William Johnson, who sowed its seeds on river-bottom farmland circa 1840.
In maturity Common Burdock is loaded with hooked bracts – cockle burrs – that attach to the clothing of humans, and imbedded in the fur of animals.
• Lesser Burdock (Arctium minus), also referred to as Common Burdock, is native to Europe.
It is such as nuisance is so many ways, growing to large size, up to five feet tall, with huge, heart-shaped leaves as big around as a basketball, but worst of all, in maturity it is loaded with hooked bracts – cockle burrs – that attach to the clothing of humans, and embedded in the fur of animals.
The large, bushy plant, grows in dense colonies, especially around outbuildings and field edges, and flowers from July through October. The flowers, which are purple, resemble thistles. The plant grows a deep taproot, up to 12 inches into the soil.
To eradicate Common Burdock spray the leaves with herbicide.
• Giant Foxtail, (Setaria faberi), is an Asian grass, a summer annual, with plants emerging from seeds in the spring, and setting seeds in the late summer or fall.
Giant Foxtail prefers compacted soils, high in nitrogen and phosphorus. The plant gains a competitive edge on crops as the soil pH increases.
Giant Foxtail was introduced into North America, where it is a significant pest of corn, reducing crop yields by 13 to 14 percent on average.
Mechanical control by tillage, rotary hoeing, or flaming is very difficult. Crop rotation with two years of alfalfa effectively reduces Giant Foxtail, and herbicides can effectively control the plant when it is growing amongst broadleaf crops, but not corn.
• Common Teasel (Dipsacus sylvestris), is native to Eurasia and North Africa, but in the U.S. is considered a noxious weed.
It forms large monocultures, by displacing other species, in areas it invades.
Its cluster of flowers, lavender in color, are in cylindrical array. They dry to a spine-tipped cone.
Teasels are easily identified with their prickly stem and leaves, and their flowers that form a head on the end of their stems.
In Kentucky, Common Teasel is a roadside weed that finds its way into dried flower arrangements.
• Japanese Knotweed (Polygonum cuspidatum), is a large, herbaceous perennial native to Japan, China, and Korea.
This invasive species has a hollow stem with distinct raised nodes that give it the appearance of bamboo.
While stems may reach a maximum height of 13 feet, it is typical to see much smaller plants. The invasive species will grow anywhere and spreads out over time. It is a determined plant, able to sprout through cracks in the pavement or concrete.
The leaves are a broad oval, the flowers small and cream or white colored.
There are several closely related species.
The Kentucky Exotic Pest Plant Council, the Kentucky affiliate of the Southeast Exotic Pest Plant Council, has the responsibility of keeping a list of the most severely noxious and invasive plant threats to Kentucky. View their current list at www.se-eppc.org.
Art Lander Jr. is outdoors editor for KyForward. He is a native Kentuckian, a graduate of Western Kentucky University and a life-long hunter, angler, gardener and nature enthusiast. He has worked as a newspaper columnist, magazine journalist and author and is a former staff writer for Kentucky Afield Magazine, editor of the annual Kentucky Hunting & Trapping Guide and Kentucky Spring Hunting Guide, and co-writer of the Kentucky Afield Outdoors newspaper column.
