Identifying and Controling Non-native Invasive Plants

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.

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.

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.

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.

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.

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.

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.

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.

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@PLC-nh.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