Identifying and Controling Non-native Invasive Plants

Autumn Olive (Elaeagnus umbellata)

Bad Habits: Creates heavy shade suppressing native vegetation.

Look For: Weedy deciduous shrub or tree (to 20'); leaves are alternate, bright green with silver-white underside, oval to lance-like and untoothed; small, light yellow flowers grow along stem after leaves appear; abundant small, round, juicy fruits are red to pink and dotted with scales.

Management:
1) Hand pull seedlings and sprouts when soil is moist.
2) Paint herbicide on cut stems and trunks of larger plants to prevent sprouting.

Native Alternatives: Winterberry, black haw viburnum, gray dogwood, serviceberry, American holly, bayberry, wax myrtle.

European Barberry (Berberis vulgaris)
Japanese Barberry (Berberis thunbergii)

Bad Habits: Escaped from cultivation and is progressively invading natural areas by crowding out native understory plants.

Look For: Dense 2-6' tall woody shrub with numerous arching spine-bearing branches; single or multiple four-part yellow flowers; ovate, up to 1" leaves ranging from green to red/purple; oblong red berries persist from fall through winter.

Management:
1) Dig small plants by gloved hand.
2) Use weed wrench to dig older plants in moist soil.
3) Cut or mow repeatedly.
4) Use herbicide to control plants in difficult locations.

Native Alternatives: Spicebush, sweet pepperbush, northern bayberry, highbush blueberry.

Oriental Bittersweet (Celastrus orbiculatus)

Bad Habits: Aggressive growth can strangle trees and shrub stems causing death to both; plants and plant communities can be over-topped and shaded out by this vine’s dense foliage.

Look For: Deciduous vine which climbs other plants by twining; branches are round, hairless, light to dark brown, and have surface bumps; outer surface of roots is bright orange; leaves are alternate and different sizes; small greenish-yellow flowers are distributed evenly along the stem; mature capsules of pea-sized yellow fruit break open revealing a bright orange-red berry (American bittersweet flowers and fruits are in clusters at ends of stems).

Management:
1) Hand pull small plants.
2) Mow small patches weekly.
3) Cut stems of larger patches; paint repeatedly with herbicide; pull upper vines out of trees.

Native Alternatives: Trumpet creeper, pipevine, passionflower.

Black Swallowort (Cynanchum louiseae)
(Also called Dog-strangle Vine)

Bad Habits: Threatens native plants in fields, forest edges, woods, and open disturbed areas; dense leafing blocks light from reaching plants that it scrambles across, often leading to their death.

Look For: Vine that grows to 10' long, climbing over other plants; shiny dark green leaves are 2-4" long, oblong to ovate with a pointed tip; fragrant dark purple flowers; seedpods and seeds are similar to, but smaller than milkweed pods.

Management:
1) Pull by hand, dig or mow twice a season.
2) Pick pods before they open.
3) Dispose of vines and pods in tightly sealed plastic bags.

Native Alternatives: Pipevine, swamp milkweed, butterfly weed.

Blunt-leaved Privet (Ligustrum obtusifolium)

Bad Habits: Forms dense thickets and out-competes native shrub species. Native wildflower species are inhibited by the dense cover it produces. Seeds are dispersed by birds and other wildlife; Can be spread by seeds and root sprouts.

Look For: Upright shrub to 12 feet with equal spread, usually with many stems; can be somewhat twiggy. Bark is smooth and grayish brown with many light colored, short, horizontal lenticels. Opposite leaves are simple, oblong, 1 to 2 inches long; dark green above and lighter below; nearly evergreen. Short panicles of fragrant white flowers are about 1/3 inch long. They appear in late spring at ends of twigs and have a displeasing odor. Small, ¼ inch fruit is a shiny, blue-black berry with a white waxy bloom. It ripens in the fall and persists through the winter.

Management: Pull seedlings by hand. Use Weed Wrench™ for stumps. Watch for new seedlings.

Native Alternatives: winterberry holly, inkberry holly, New Jersey tea, bayberry, wild hydrangea, ninebark, silky dogwood, arrow-wood or nannyberry.

Bohemian Knotweed (Polygonum x bohemicum)

Bad Habits: Dense thickets spread very quickly in disturbed sites, roadsides, riparian and wetland areas, degrading and excluding native vegetation by altering natural ecosystems. A pea-size root piece can develop into a mass of plants in a matter of a few years. Persistent root systems can damage any paved surface and building foundation. (Note: Bohemian Knotweed is a cross between giant knotweed and Japanese knotweed.)

Look For: Herbaceous perennial with stout, hollow, reddish brown stems which can grow to 10 feet tall. Stem nodes are swollen and surrounded by thin papery sheaths. Leaves range from heart to spade shaped. Pubescence on leaf underside is spike-like as opposed to small bumps on Japanese Knotweed and long hairs on Giant Knotweed. Flowers are small, creamy white to greenish white and grow in upright, showy plume-like branched clusters from leaf axils. Fruit is 3-sided, black and shiny. Reproduces by root or stem parts although a low percentage of seeds can be viable. Roots can spread horizontally up to 30 feet from the parent plant.

Management: Careful digging is effective for small populations; removal of all roots is important to avoid resprouting from rhizomes. Repeat stem cutting during the growing season. Responds to chemical controls poured down cut stems.

Native Alternatives: winterberry holly, spicebush, buttonbush, silky willow, pussy willow, American elderberry, alder, Joe-Pye weed.

Common Buckthorn (Rhamnus cathartica)
Glossy Buckthorn (Rhamnus frangula)

Bad Habits: Forms thick, even-aged thickets, creating a continuous canopy of dense shade; invades open woodlands, forest edges and abandoned pastures (glossy buckthorn invades wetlands); causes habitat degradation and shades out rare species.

Look For: Deciduous shrub or small tree (to 20'). Common buckthorn has 2" oval leaves, smooth on both sides and edged with fine teeth; leaf veins curve toward the leaf tip; twigs may be tipped with sharp thorns. Glossy buckthorn leaves are shiny, hairy or smooth underneath and lack teeth. Both produce black berries.

Management:
1) Hand pull or dig with weed wrench.
2) Cut stems at ground level and paint with herbicide repeatedly.
3) Girdle and underplant canopy with native plants.

Native Alternatives: Serviceberry, spicebush, wild hydrangea, lowbush and highbush blueberry, mapleleaf viburnum, winterberry.

Burning Bush (Euonymus alatus)

Bad Habits: Makes dense thickets crowding out native herbs and shrubs; tolerates wide variety of growing conditions.

Look For: Shrub with a feathery-layered appearance; gray/brown bark has “wings” or ridges; opposite, elliptic leaves turn red in fall and then drop off; smooth, purple/red fruit contain about four red seeds.

Management:
1) Hand pull seedlings out of moist soil or dig out.
2) Cut trunks or stems of larger plants and grind stumps.
3) Paint cuts with herbicide to prevent sprouting, watching for sprouting from old roots.

Native Alternatives: Serviceberry, spicebush, wild hydrangea, lowbush and highbush blueberry, mapleleaf viburnum, ‘Mountain Fire’ andromeda, winterberry.

Dame's Rocket (Hesperis matronalis)

Bad Habits: Can form dense beds, particularly in open woodland borders, roadsides and floodplains. Grows in full sun or shade; out competes native vegetation and dominates natural areas.

Look For: Biennial or perennial up to 3 feet; produces terminal clusters of fragrant flowers with 4 purple, pink or white petals. (Note: Do not confuse with Garden Phlox which has 5 petals). Blooms in late May to June. Alternate leaves are lance-ovate and are sharply toothed. Fruits are long 2-4 inch pods.

Management: Rapid removal after sighting for 2-5 years to prevent seed production. Hand pull or dig until seed bank is exhausted. Use chemical control responsibly in late fall or early spring. Reduce foot traffic, overgrazing and erosion.

Native Alternatives: garden phlox, columbine, jack-in-the-pulpit, wild geranium, Joe-Pye weed.

Garlic Mustard (Alliaria petiolata)

Bad Habits: Rapidly dominates and displaces many native spring wildflowers; spreads by seeds.

Look For: Biennial; 1-4' in height; clusters of small white flowers, each with four petals in the shape of a cross; stalked, triangular to heart-shaped, coarsely toothed leaves give off an odor of garlic when crushed; first-year plants appear as a rosette of green leaves close to the ground, remaining green throughout the winter and developing into mature flowering plants the following spring.

Management:
1) Hand pull or cut to ground level until seed bank is exhausted.
2) Smother infestation for several years.
3) Apply herbicide.

Native Alternatives: Wild ginger, lady fern, wood fern, foam flower, creeping phlox.

Giant Hogweed (Heracleum mantegazzianum)
(Also called Giant Parsnip)

Bad Habits: Outcompetes native plants for habitat, especially in moist and rich streamside soils and in disturbed areas; poisonous sap causes skin to become very sensitive to UV radiation causing blisters, itching and severe burns.

Look For: Biennial or perennial flowering plant that grows 8-15' in height; flat-topped, white, cow parsnip-like flower can be up to 21/2' across; thick hollow stems have purple blotches and coarse hairs; fruits are dry and elliptic shaped.

Management: Contact NH Department of Agriculture who will handle control measures.

Native Alternatives: Joe Pye weed, boneset, elderberry, arrowwood viburnum.

Morrow’s Honeysuckle (Lonicera morrowii)
Showy Bush Honeysuckle (Lonicera x bella)
Tatarian Honeysuckle (Lonicera tatarica)

Bad Habits: Alters natural habitats by decreasing light and depleting soil moisture and nutrients for native species; competes with native plants for pollinators resulting in reduced seed set for native species.

Look For: Six-20' deciduous shrub; short stalked 1-2" ovate to elliptic leaves; tubular flowers grow in leaf axils (Morrows: white/yellow, Tatarian: white or pink, Showy Bush: pink); fruits are red to orange; older stems are hollow (native honeysuckle stems are not).

Management:
1) Hand dig small plants.
2) Uproot with weed wrench.
3) Cut repeatedly or girdle.

Native Alternatives: Serviceberry, spicebush, wild hydrangea, lowbush and highbush blueberry, northern bayberry, arrowwood or mapleleaf viburnum.

Japanese Honeysuckle (Lonicera japonica)

Bad Habits: Vigorous colonizer that climbs, drapes and smothers most vegetation in its path in its attempt to reach light.

Look For: Semi-evergreen vine; opposite and short-stalked oblong leaves (native “vine honeysuckle” leaves are united at base); fragrant white to yellow flowers; small black fruit.

Management:
1) Pull entire vine or dig root system repeatedly.
2) Mow large patches and follow-up with repeated herbicide application.

Native Alternatives: Trumpet creeper, Virginia creeper, climbing hydrangea.

Japanese Knotweed (Polygonum cuspidatum)

Bad Habits: Creates dense canopy shading out native plants and trees; grows as monoculture along roadsides and stream banks; strong root system can break pavement.

Look For: Large masses of plants growing to 9' tall; heart shaped leaves on bamboo-like stalks; ample white flowers grow in linear clusters.

Management:
1) Remove plants before they become established.
2) Repeat cutting of large plants, four or more times a season.
3) Apply herbicide to regrowth of newly cut plants.

Native Alternatives: Sweet pepperbush, maleberry, silky dogwood, elderberry.

Japanese Stilt Grass (Microstegium vimineum)

Bad Habits: Grows in full sun to full shade and in moist or dry areas. Invades and spreads aggressively in disturbed areas, floodplains, mowed areas and soil-disturbed areas by deer. Also occurs in forested wetlands, thickets, stream banks, uplands and roadside ditches. Spreads by rooting at stem joints and by seed; up to 200 seeds from a mature plant may remain viable in the soil for 3 years. Eliminates native plants.

Look For: Annual grass with weak stems. Resembles delicate bamboo. Forms a mat and may grow to 2-3 feet. Pale green leaves are lance-shaped and are 3 inches long with shiny mid-rib. Flowers in late summer. After fruiting entire plant dies.

Management: Hand pulling is easy as roots are shallow rooted. Mow or weed whip flowering plants prior to seed production. Chemical control.

Native Alternatives: wild ginger, lady fern, wood fern, foam flower, creeping phlox.

Mile-a-Minute Vine (Polygonum perfoliatum)

Bad Habits: Grows up to 6 feet per day, growing over existing plants, limiting their photosynthesis and causing their death. Found in disturbed open areas, roadsides and abandoned fields.

Look For: Annual, herbaceous scrambling vine with branching stems up to 26 feet long. Stems with downward pointing barbs; pale green initially, turning reddish with age. Alternate leaves are pale green, triangular and attach to the long petiole on the blade’s underside just above the base. Small greenish-white flowers in spike-like groupings, often stay closed. Green berries turn metallic blue as they ripen.

Management: Rapid removal after sighting to prevent spread. Hand pull seedlings and vines using gloves. Use chemical control along with a surfactant to cut through the waxy covering.

Native Alternatives: virgin’s bower, bearberry, bunchberry, lowbush blueberry, checkerberry or wintergreen.

Multiflora Rose (Rosa multiflora)
(Also called Rambler Rose)

Bad Habits: Can dominate a forest understory by creating dense, impenetrable thickets that crowd out other vegetation; inhibits regrowth of native plants and ultimately slows down forest regeneration; grows in moist and dry soil.

Look For: Robust perennial shrub with thorny arching stems; alternately arranged compound leaves with seven or nine leaflets; large clusters of fragrant white or pink flowers bloom in June and July; small red hips are eaten and transported by birds.

Management:
1) Cut small infestations repeatedly.
2) Bulldoze large areas and dispose of responsibly.
3) Apply herbicide to leaves.

Native Alternatives: Common blackberry, flowering raspberry, pasture rose, swamp rose.

Norway Maple (Acer platanoides)

Bad Habits: Creates dense shade displacing native trees, shrubs, and herbs; roots may emit a toxin which is deadly to other plants.

Look For: Grows to 90'; rounded crown; smooth bark when young, changes to rough when older; milky sap in leaf stems (sugar and red maples have clear sap); dark green leaves are opposite along twigs; winged seeds. All varieties of Norway maple, including the red leafed “Crimson King”, are invasive.

Management:
1) Pull seedlings by hand.
2) Girdle trunk.
3) Cut larger trees and sprouts to ground and paint cuts with a brush herbicide.

Native Alternatives: Sugar maple, black gum, willow oak, American beech, red maple, sweet gum, sourwood.

Pale Swallow-wort (Cynanchum rossicum)

Bad Habits: Forms dense colonies that are almost impossible to eradicate, breaking apart when dug up. Invades and quickly overwhelms pastures, farmlands, wildlife sanctuaries and roadsides. Displaces native vegetation reducing insect and bird populations. Monarch butterflies mistake this plant for milkweed and cannot get nourishment.

Look For: Herbaceous, twining vines with pale-purple to yellowish flowers that are covered in white hairs. Petals are almost twice as long as they are wide and have no hairs. Slender, 2-3” long seed pods contain seeds that are surrounded by “fluff” which floats and spreads great distances. (Note: Black swallowwort flowers are dark purple and petals have hairs).

Management: Early detection and removal is the best approach. Pull seedlings by hand. For large established infestations herbicide controls are most effective immediately after flowers appear.

Native Alternatives: Once swallow-worts are eradicated, plant pastures with grains and grasses.

Perennial Pepperweed (Lepidium latifolium)

Bad Habits: Forms dense stands in salt marshes; often well above high tide mark where it can raise the soil salt table, adversely affecting nesting habitat and food quality for birds. Also found along roadsides and in agricultural fields and pastures. Produces numerous seeds per plant and has the ability to spread via very persistent rhizomes resulting in monospecific stands that displace native flora and fauna.

Look For: Herbaceous perennial, 2-1/2 to 5 feet tall perennial forming a woody crown at the soil line from which new shoots grow; Old stems overwinter with rosettes of leaves at the base. Stems and foliage are waxy, bright or gray-green. Dense clusters of white flowers bloom in early summer and continue throughout the season.

Management: Remove scattered plants and watch for resprouting. Large infestations require intensive herbicide application.

Native Alternatives: Queen Ann’s lace, turtlehead, bluebead lily, Solomon's seal, bloodroot, milkweed, New England or New York aster, Joe-Pye weed.

Spotted Knapweed (Centaurea biebersteinii DC)

Bad Habits: Secretes chemicals into soils that kill surrounding plants. Each plant can produce an average of 1,000 seeds, allowing a population to spread rapidly. Can live in a wide range of habitats and quickly take over native fields and grasslands.

Look For: Biennial or short-lived perennial living for three or more years. Typically grows 3-4 feet. Pale, slender leaves grow from 1-3 inches in length and are alternate on the stem. Leaf surface is rough. Pinkish-purple flowers measure up to 3/4 inch. Each flower head has stiff (bracts) leaves at the base of the flower that have fine vertical streaks tipped with dark, comb-like fringes giving the flower head a spotted appearance. Seeds are brownish in color, smaller than 1/4 inch in length and have a notch on one side of the base. The short tuft of bristles at the tip help seeds disperse in the wind. Has a stout taproot.

Management: Pull isolated plants including entire root by hand when the ground is damp. Bag flowering plants and remove from site. Individual plants or small populations of knapweed should be controlled before they become large populations. A few chemicals that slow or kill plant growth can work well, but can also damage sensitive natural areas if they are not applied carefully. Read label carefully.

Native Alternatives: turtlehead, bluebead lily, Solomon's seal, bloodroot, milkweed, New England or New York aster, Joe-Pye weed.

Purple Loosestrife (Lythrum salicaria)
Learn about the PLC Purple Loosestrife Program

Bad Habits: Displaces native flora and fauna by forming monocultures in a variety of habitats, especially in wetlands.

Look For: Stands of single and multi-stalked plants up to 6' in height; opposite or whorled leaves on four- to six-sided woody stems; dense spike of purple flowers bloom in July and August.

Management:
1) Remove all root matter by digging and responsibly disposing of in bags. Watch for new plants every year.
2) Introduce biological control.
3) Remove and dispose of flower heads before they go to seed to limit seed dispersal.

Native Alternatives: Joe Pye weed, cardinal flower, gayfeather, obedient plant, blue vervain.

For more information call 487-3331, or email plc@plcnh.org

Thanks to the New England Grassroots Environmental Fund for support of this publication.

Photo Credits
Friends of Fresh Pond Reservation
Lynette Lombard, Piscataquog Watershed Association
Jennifer F. Orth
Hannah Proctor, Piscataquog Watershed Association
John M. Randall, The Nature Conservancy