Japanese knotweed is a lump forming, semi-woody perennial three to 10 feet high. It produces sprays of small greenish-white flowers in late summer. The hollow stems are smooth with purple specks and have distinct nodes at leaf attachments. It is shade tolerant, thrives in a variety of soil and moisture conditions, and is commonly found along streams, rivers, or disturbed areas. Japanese knotweed can best be identified by hollow, bamboo-like stems with purple flecks and prominent nodes at leaf attachments. In late summer, sprays of green-white flowers are evident. Leaves are simple, alternate and generally oval with a flat base and pointed tip. New leaves may start out red and turn green in maturity. To learn more about it, how to control it and to see additional photographs go to the Lower Hudson PRISM website. The New York Invasive Species (IS) Information through the Cornell Cooperative Extension also has excellent information including a useful video on how to best manage it. The Connecticut Invasive Plant Working Group suggests that to remove it one should hand pull young plants. For small populations, repeat cutting 3x per year over several seasons may be effective. Bag and dispose of all plant parts as trash. Do not compost. Biological controls are under review. Japanese Knotwood may be confused with the native Pokeweed. Learn more about Pokeweed on the Northwest Michigan Invasive Species Network.
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- Japanese Knotweed (Reynoutria japonica; also, Fallopia japonica, Polygonum cuspidatum) - nn image
Invasives Species
Barberry (Berberis thunbergii)
Japanese barberry is a dense, deciduous, spiny shrub that grows 2 to 8 ft. high. The branches are brown, deeply grooved, somewhat zig-zag in form and bear a single very sharp spine at each node. The leaves are small (½ to 1 ½ inches long), oval to spatula-shaped, green, bluish-green, or dark reddish purple. Flowering occurs from mid-April to May in the northeastern U.S. Pale yellow flowers about ¼ in (0.6 cm) across hang in umbrella-shaped clusters of 2-4 flowers each along the length of the stem. The fruits are bright red berries about 1/3 in (one cm) long that are borne on narrow stalks. They mature during late summer and fall and persist through the winter. Visit the Plant Conservation Alliance’s Aline Plant Working Group site to learn more about it as well as page 20 of the Lower Hudson Valley PRISM, Best Management Practices for Common Invasive Plants.
Black Swallowwort (Cynanchum louiseae)
Black Swallowwort is a member of the Dogbane family (Apocynaceae). A six-to-seven-foot vine with long oval leaves. Tear-drop seed pods contain hundreds of seeds each with a tuft of white hair. Flowers are dark purple..
A thorough description of the plant including photos, its habitat, and the best way to remove it is found on Lower Hudson Prism.
Burning Bush (Euonymus alatus) - nn image
A deciduous bushy shrub in the bittersweet family (Celastraceae). Grows to 20 feet tall. Green to brown stems have corky wings. Elliptic leaves are one to three inches long and ½ to 1 ¼ in wide and turn bright red in the fall. Small green flowers occur in the spring and small tooth red-orange fruits turn purple in the fall. To eradicate it, hand pull seedlings up to two feet tall. Larger plants must be cut or dug out. Learn more on how to control it and review additional photographs on Lower Hudson PRISM. View descriptions and photographs of plants with which it may be confused on NY Botanical Garden.
Common Reed Grass (Phragmites australis) - nn image
Phragmites australis is a non-native, invasive, wetland, perennial reed grass. Phragmites spreads aggressively by rhizomes and seeds and quickly outcompetes and displaces native salt marsh vegetation while providing little or no food or shelter for most saltmarsh-dependent wildlife. Additionally, Phragmites can eliminate small intertidal channels and decimate pool habitats that should offer natural refuge food for invertebrates, fish and waterbirds. Non-native Phragmites is distinctive due to the extensive dense colonies it forms and plume-like seedheads that generally persist through the winter on canes that range in height from 6 feet-15 feet tall and remain standing throughout the year. For more information go to the Bugwood wiki site. To best remove very small stands: Hand-dig, being sure to remove the entire rhizome system; or smother by covering with heavy-duty black plastic (after cutting and removing stems) for at least two years; or cut stems repeatedly below water level. Replant with native species. Removing larger stands will need professional removal and monitoring to protect the surrounding habitat during the process and ensure successful removal.
English Ivy (Hedera helix)
English Ivy is a non-native invasive evergreen vine that covers and kills trees. Vines climbing up tree trunks envelope branches, blocking sunlight from reaching the host tree’s foliage, impeding photosynthesis. For additional information look at Invasive.org. And check out a short video demonstrating removal of vine. It can often be confused with poison ivy and Virginia Creeper.
Garlic Mustard (Alliaria petiolate)
Garlic Mustard is a biennial herb in the Mustard family (Brassicaceae). First year plants are low rosettes of kidney shaped leaves. Second year plants produce flowering stalks 1-4 feet high that die back by late spring. Flowers have four petals and occur in small button shaped clusters. Fruits are slender, erect capsules (siliques) and seeds are 2.5-3 mm long, slender and tan to dark. Highly invasive and difficult to control. To learn more about it, how to control it and to see additional photographs go to Lower Hudson PRISM.
Giant Hogweed (Heracleum mantegazzianum)
Giant Hogweed is a Federally-listed noxious weed. The sap, when combined with sunlight and moisture (sweat), can cause severe burns and scarring. It can reach a height of 20 feet. The thick, hollow stems have dark purplish blotches and raised nodules. The leaves are compound, lobed, and deeply incised and can reach up to five feet in width. White umbrella-shaped flowers, resembling the flowers of Queen Anne’s lace, appear in early to mid-summer. It grows in disturbed places like roadside ditches and stream banks and prefers rich moist soil and full to partial sun.
Non-professionals should not attempt to remove, or even touch, giant hogweed. If you encounter the plant, report it to the NYSDEC at: 845-256-3111. From late April through August, DEC field crews visit each confirmed giant hogweed site, and use appropriate control method. This is free of charge to the landowner.
Except for its giant size, giant hogweed resembles cow-parsnip and Queen Anne’s lace.
To learn more about it, and to see additional photographs, go to NY Department of Environmental Conservation.
Glossy Buckthorn (Frangula alnus)
Glossy Buckthorn is a deciduous shrub or small tree easily identifiable by its thornless branches and stems, which are covered by fine, wooly brown hairs. The leaves are simple, dark green and shiny on top. It prefers moist soils and tolerates sun, but thrives in shade. It is commonly found in disturbed places like roadsides and fields. Glossy buckthorn has insignificant yellow-green flowers at leaf axils in spring. followed by dark purple berries in summer and fall. The bark is dark gray or brown with white lenticels.
Common buckthorn (Rhamnus frangula), also invasive, is a similar species but the outer bark is dark gray and the inner bark is orange.
Pulling by hand or via a weed wrench is an effective method of control for seedlings and smaller plants. Regular mowing where possible will reduce or halt fruiting. Successive cuttings twice a season for at least 3 years, will reduce the size and density of infestations but will likely not eradicate it. Larger stems may be girdled and re-sprouts clipped as they emerge.
Smooth Alder, or Hazel Alder (Alnus serrulata) can be confused with glossy buckthorn, but the leaves have a rough, toothed margin instead of a smooth. Also, throughout much of the year, smooth alder holds soft cones, or catkins, which are very different from the juicy berries of glossy buckthorn.
To learn more about it, and to see additional photographs go to Lower Hudson PRISM as well as PennState Extension.
Japanese Angelica Tree (Aralia elata)
Japanese Angelica Tree is a member of the Carrot family is capable of growing forty feet high. This species blooms white flowers wider than they are tall in late August. Stems are covered in sharp spines and small purple fruits generally appear in September. Manual hand pulling and digging of young plants. A weed wrench much be used for larger plants. May be confused with Devil’s walkingstick (Aralia spinosa).
To learn more about it, and to see additional photographs, go to Lower Hudson PRISM,
Japanese Knotweed (Reynoutria japonica; also, Fallopia japonica, Polygonum cuspidatum) - nn image
Japanese knotweed is a lump forming, semi-woody perennial three to 10 feet high. It produces sprays of small greenish-white flowers in late summer. The hollow stems are smooth with purple specks and have distinct nodes at leaf attachments. It is shade tolerant, thrives in a variety of soil and moisture conditions, and is commonly found along streams, rivers, or disturbed areas. Japanese knotweed can best be identified by hollow, bamboo-like stems with purple flecks and prominent nodes at leaf attachments. In late summer, sprays of green-white flowers are evident. Leaves are simple, alternate and generally oval with a flat base and pointed tip. New leaves may start out red and turn green in maturity. To learn more about it, how to control it and to see additional photographs go to the Lower Hudson PRISM website. The New York Invasive Species (IS) Information through the Cornell Cooperative Extension also has excellent information including a useful video on how to best manage it. The Connecticut Invasive Plant Working Group suggests that to remove it one should hand pull young plants. For small populations, repeat cutting 3x per year over several seasons may be effective. Bag and dispose of all plant parts as trash. Do not compost. Biological controls are under review. Japanese Knotwood may be confused with the native Pokeweed. Learn more about Pokeweed on the Northwest Michigan Invasive Species Network.
Japanese Stiltgrass (Microstegium vimineum)
An annual grass growing up to 3 feet but often shorter. It forms dense stands in woodland edges and semi-open areas. It prefers moist, partially shaded sites but tolerates full shade. Go to Lower Hudson PRISM to learn about its identifying features and best removal approach. The New York Botanical Garden (on page 30-31) has good information about the native plant Whitegrass that often grows with and resembles Japanese Stiltgrass.
Jetbead (Rhodotypos scandens)
Jetbead is a multi-stemmed deciduous shrub that invades understories despite shade. Most noticeable for its flowers. Grown as a desired ornamental in China and Japan, it quickly outcompetes native shrubs and can grow five to seven feet tall disturbing canopy layers. Single, white showy flowers appear on sprawling shrubs in early May often at forest edges. The berries grow perpendicularly to each other and are jet black. Leaves are deeply veined, elongated and toothed - they grow directly opposite of each other.
Currently it is a less common invasive species in Hudson Valley, if you see it, please document its presence by loading photos onto iNaturalist
Jetbead is confused with native mock orange (Philadelphus virginalis) which has similar four petaled white flowers. The native Arrowood (Viburnum dentatum) is a lookalike but the leaves are softer and rounder.
To learn more about it, and to see additional photographs, go to Lower Hudson PRISM.
Lesser Celandine (Ficaria verna)
Lesser celandine is a member of the buttercup family, lesser celandine is a spring ephemeral with glossy yellow flowers and dark green, heart-shaped leaves. It forms dense mats in riparian corridors, forested floodplains, wet meadows, and lawns, preventing the growth of other plants. By summer, lesser celandine dies back and disappears completely. The plant propagates primarily by small potato-like tubers that can be disbursed by water and digging animals. Once separated from the parent plant, each tuber has the potential to grow into a new plant.
Due to its ephemeral nature, lesser celandine is challenging to control. Small infestations can be hand dug if care is taken to remove all the roots and tubers. The controlled area should be revisited two to three times a season for at least two to three years to ensure exhaustion of the seed bank and that no re-sprouting has occurred. Removed plants should be bagged and disposed of in trash.
Lesser celandine and the native marsh marigold (Caltha palustris) are both spring ephemerals of wet areas with similar buttercup-like flowers. The flowers of marsh marigold have five to nine yellow petal-like sepals while lesser celandine has seven to12 narrow yellow petals with green sepals underneath. Marsh marigold has fleshy roots with no tubers.
To learn more about it, how to control it and to see additional photographs go to Lower Hudson PRISM as well as the New York Invasive Species (IS) Information through the Cornell Cooperative Extension.
Mile a Minute (Persicaria perfoliata)
Mile a Minute is a species of flowering plant in the buckwheat family. Also called Devil’s tearthumb, it is a trailing annual vine with barbed stems and triangular leaves. It is vigorous, and smothers other herbaceous plants, shrubs and even trees. To learn more about it, how to control it and to see additional photographs go to the Lower Hudson PRISM website as well as the New York Invasive Species (IS) Information through the Cornell Cooperative Extension.
Mugwort (Artemisia vulgaris), with common names, mugwort, wormwood, cronewort - nn image
Clump-forming invasive perennial flowering herb with woody stems up to 5 feet high and deeply lobed alternate leaves with hairy undersides. Blooms July - October. Often found on forest edges, roadsides, waste places and in turf grass, as well as home gardens. When crushed, leaves have a spicy, sage-like aroma. It was introduced into North America from Europe and Eastern Asia, where used medicinally, primarily as a digestive. Spreads aggressively, primarily by rhizomes, and is highly threatening to native plants. To learn more about it, how to control it and to see additional photographs go to the Lower Hudson PRISM website. Also the New York Invasive Species (IS) Information . Also the New York Invasive Species (IS) Information through the Cornell Cooperative Extension also has excellent information including ways to manage mugwort. And, finally in New York undertook a large project to eradicate Mugwort in Caumsett State Park in Huntington, NY.
Multiflora Rose (Rosa multiflora)
Dense efflorescent shrub first introduced from Asia that spreads rapidly in open woods, pastures and woodland edges and can climb into trees. Reproduces by dispersal of millions of seeds that may remain in the soil for twenty years and are widely distributed by birds. Creates large, impenetrable thorny, thickets that exclude native plants and inhibit movement and foraging of native wildlife. To learn more about it and see additional photos, please visit the Lower Hudson Lower Hudson PRISM website as well as page 67 of the Lower Hudson Valley PRISM, Best Management Practices for Common Invasive Plants. The New York Botanical Garden (on pages 18-19) has good information about the native Rose plants that are often confused with Multiflora Rose.
Norway Maple (Acer platinoides)
Norway Maple is a widely distributed invasive tree that outcompetes all other terrestrial species by virtue of producing dense, dark shade and exuding chemicals from roots that impede growth of other plants. Trees support almost zero species of insects, birds or wildlife. A milky white sap is exuded when a petiole is detached from a tree or veins of leaf are cut. The sap of other maples is clear by comparison. It has broad, full leaves with narrow tips at the end that stay green late into the fall. Additionally, the pattern of the bark is up and down and it is deeply grooved. It may be confused with the Sugar maple and Red maple
To learn more about it, and to see additional photographs as well as a video go to the Lower Hudson PRISM website. The Best Management Practices for Priority Invasive Plants in the Lower Hudson Valley, page eight, and Norway Field Identification.
Oriental Bittersweet (Celastrus orbiculatus)
Oriental Bittersweet is a climbing perennial/woody plant that is known for its colorful red fruit and spade-shaped leaves. This fast-growing vine often wraps and strangles the surrounding vegetation, including trees, becoming thicker with age. It has white/green blossoms in spring and is spread by birds and by people who find it attractive. To learn more about it and to see additional photographs go to the Lower Hudson PRISM website as well as the Ulster County Cornell Cooperative Extension. To learn about ways to manage it, go to the Bugwood Wiki site. Oriental Bittersweet can be confused with native American Bittersweet; there is some evidence that the two species have hybridized, although the extent of this is unknown.
Oriental Lady’s Thumb (Persicaria longiseta, Polygonum cespitosum)
Oriental Lady’s Thumb is an annual that produces thousands of hard-coated seeds and distinctive pink flowers. It can grow as long as six to 30 inches, either erect or sprawling. Oriental lady's thumb is classified as a widespread nonnative species that is restricted to disturbed areas and is not invasive in undisturbed habitats
To learn more about it, and to see additional photographs, go to iNaturalist.
Porcelain Berry (Ampelopsis brevipedunculata; also known as Amur peppervine) - nn image
Porcelain Berry is a vigorous, woody, deciduous, tendril-climbing vine that is somewhat similar in habit to wild grape vines and will typically grow 15-25 feet. It features mostly 3-lobed, deep green leaves (to 5 inches long). Clusters (cymes) of non-showy, greenish flowers appear in the leaf axils in July. Its flowers give way in fall to showy clusters of rounded-to-oval, pale lilac-blue fruits which mature to brighter and deeper shades of blue. The New York Botanical Garden (on pages 28-29) has good information about the native Grape Vines that may be confused with Porcelain Berry.
Purple Loosestrife (Lythrum salicaria)
Purple Loosestrife is an herbaceous, multi-stemmed wetland perennial up to two to three meters tall, becoming woody at base. Has opposite leaves with smooth margins, and a terminal spike of showy, pinkish-purple flowers.
Although it may be controlled mechanically and by chemicals, it has been effectively controlled biologically by the release of beetles and weevils.
To learn more about it, and to see additional photographs, go to Lower Hudson PRISM.
Spotted Lanternfly
Spotted lanternfly is an invasive pest from Asia that poses a very significant threat to New York’s agricultural and forest health.
Adults and nymphs feed on sap of over 70 plant species but their preferred food source is Tree of Heaven (Ailanthus altissima). Spotted lanternfly can jump and fly short distances but they spread primarily through human activity. SLF lay eggs on firewood, furniture, stone and vehicles which are transported moving it to new areas.
Information from the NYS Department of Environmental Conservation states that ‘Nymphs are black with white spots and turn red before transitioning into adults. They can be seen as early as April. Adults begin to appear in July and are approximately one inch long and half-inch wide at rest, with eye-catching wings. Their forewings are grayish with black spots. The lower portions of their hindwings are red with black spots and the upper portions are dark with a white stripe. In the fall, adults lay one-inch-long egg masses on nearly anything from tree trunks and rocks to vehicles and firewood. They are smooth and brownish-gray with a shiny, waxy coating when first laid.’You will also view excellent photos of egg masses, as well as the different stages of development.
The best way to control spotted lanternfly is to prevent its spread. Learn to identify it and to report it right away. Always inspect outdoor items such as firewood, vehicles, and furniture for egg masses. If you visit states with Spotted Lanternfly, be sure to check all equipment and gear before leaving and scrape off any egg masses. If you believe you have found Spotted laternfly, take photos (including something for scale, such as a coin, or ruler) and send an e-mail to .
Tree of Heaven (Ailanthus altissima)
Tree of Heaven is a fast growing, colony -forming deciduous tree of disturbed places. When crushed, the leaves and branches have a distinctive smell often compared to rancid peanut butter. Tree of heaven tolerates a variety of soils, and sun or shade conditions. It is the preferred host of the invasive insect, Spotted Lanternfly. Tree of heaven flowers in June with showy clusters of small, yellow-green flowers, which are followed by papery winged seeds (samaras) in late summer and fall. The compound leaves have 10-40 leaflets with smooth leaf margins. Each leaflet has one or more rounded teeth near its base with a thickened gland on the underside of each tooth. When crushed, leaves and branches release an odor often compared to rancid peanut butter. Learn more about it and review additional photographs on Lower Hudson PRISM.
To best remove it, seedlings or small trees can be hand pulled when soil is moist to ensure all roots are removed. Early detection and removal of seedlings can prevent spread. Mowing is not recommended as roots may resprout. ”Cut and dab” may be effective for large trees. Gloves and protective clothing are recommended when handling Tree of Heaven as sap can cause skin irritation. The Western NY PRISM on management practices is excellent.
Wineberry (Rubus phoenicolasius)
Wineberry, a member of the Rose family is a deciduous shrub with thorny canes that can grow up to 9 feet in length. These arching, thorny canes can be identified by their distinctive red hairs, but most easily identified in July when their raspberry-like fruits are present. Please see the Lower Hudson PRISM website to learn about its Identifying Features and Best Removal Approach
Yellow Flag Iris (Iris pseudacorus)
Yellow Flag Iris (Iris pseudacorus) also known as the Yellow Flag, Yellow Iris, or Water Flag
Yellow Flag Iris is a species of flowering plant in the family Iridaceae that has invaded wetlands and other aquatic habitats. It is native to Europe, western Asia and northwest Africa. Its specific epithet pseudacorus means "false acorus", referring to the similarity of its leaves to those of Acorus calamus (sweet flag), as they have a prominently veined mid-rib and sword-like shape. However, the two plants are not closely related. The sword-like leaves are flat, erect and linear with a raised midrib. The dark to blue-green blades are 25-90 cm long and have sharply pointed tips. The flowering stems are usually similar in size to the leaves (50 to 100 cm in length). Flowers are pale to bright yellow or cream colored and seven to nine centimeters wide. The large seed pod is three -sided and angular and turns from glossy green to brown as it ripens. Each pod contains dozens of seeds densely arranged in 3 rows. Roots are 10-30 cm in length, and the fleshy rhizomes are one to four centimeters diameter.
Small clumps can be dug out, though this is only effective if the rhizomes are entirely removed. Mowed plants will regenerate from the rhizomes, so plants must be cut multiple times to exhaust their energy reserves. The sap may cause skin irritation, so gloves should be worn when handling cut or otherwise damaged stems.
To learn more about it, and to see additional photographs, go to New York Invasive Species (IS) Information.