Non-Native Invasive Plant Species

 

The following garden plants and weeds are already causing significant changes to natural areas in the Mid-Atlantic. Measures for  controlling  each species are indicated by the number in parentheses, e.g., (3). For more information about non-native invasive plants, visit www.epa.gov/reg3esd1/garden/invasives/htm

There are alternatives to invasive species in our area; native plants. Native plants are well adapted to our environment and need little care, are attractive to birds and butterflies, and are an important part of the food web for our indigenous species. 

Most Invasive Non-Native Weeds

Garlic Mustard (Alliaria petiolata, A. officinalis) A white-flowered biennial with rough, scalloped leaves (kidney, heart, or arrow-shaped), recognizable by the smell of garlic and taste of mustard when its leaves are crushed. (The odor fades by fall.)

Control: Pull before it flowers in spring (1), removing crown and roots. Tamp down soil afterwards. Once it has flowered, cut (2), being careful not to scatter seed, then bag and burn or send to the landfill. (11) may be appropriate in some settings.

Japanese or Vietnamese Stilt Grass, Eulalia (Microstegium vimineum) Can be identified by its lime-green color and a line of silvery hairs down the middle of the 2-3" long blade. It tolerates sun or dense shade and quickly invades areas left bare or disturbed by tilling or flooding. An annual grass, it builds up a large seed bank in the soil.

Control: Easily pulled in early to mid-summer (1) - be sure to pull before it goes to seed. If seeds have formed, bag and burn or send to landfill. Mowing weekly or when it has just begun to flower may prevent it from setting seed (3). Use glyphosate (11) or herbicidal soap (less effective) on large infestations. Follow up with (5) in spring.

Mile-A-Minute Vine, Devil's Tail Tearthumb (Polygonum perfoliatum) A rapidly growing annual vine with triangular leaves, barbed stems, and turquoise berries in August which are spread by birds. It quickly covers and shades out herbaceous plants.

Control: same as for stilt grass.

Japanese Perilla, Beefsteak Plant (Perilla frutescens) Sold as a salad plant, this member of the mint family is extremely invasive by wind-borne seeds. Recognize it by the odd odor, supposedly like raw beef, when you rub it.

Control: (1); (2); (10) or (11).

Spotted Knapweed (Centaurea maculosa) A biennial with thistle-like flowers.

Canada Thustle, Bull Thistle (Cirsium arvense, C. Vulgare) Exotic thistles are far more common than native ones. If you cannot identify the species, it is probably better to remove it.

Control: Do NOT pull (1) unless the plant is young and the ground is very soft - the tap root will break off and produce several new plants. Wear sturdy gloves. (2); (6); (10) or(11).

Non-Native Ornamental Grasses

Often promoted as native plants, most ornamental grasses come from outside our region. Once established, they are extremely tenacious. They are now spreading into our meadows. So far, Pampass Grass (Cortaderia selloana and C. jubata), Japanese Silver Grass (Miscanthus sinensis), and Reed Canary Grass (Phalaris arundinacea) have been the most invasive. Those with heavy seeds are less likely to spread.

Control: (1); (2); or (11), using additional sticker-spreader.


Invasive Ground Covers

 

Crown Vetch (Coronilla varia) has striking pink flowers. Its bare woody stems are unattractive in winter. Often planted along highways, its seeds spread invasively.

Control: (1); (10) or (11).

Creeping Bugleweed (Ajuga reptans), Mints, including Spearmint (Mentha spicata), Ground Ivy (also Gill-Over-the-Groundor Creeping Charlie, Glechoma hederacea), Henbit (Lamium amplexicaule), and Purple Dead Nettle (L. purpureum) spread by wind-borne seed as well as by runners. They grow in sun and shade and are common lawn weeds which have spread to woods and wetlands. Recognize mints by square stems and a minty smell when crushed. PLANT CULINARY AND ORNAMENTAL MINTS IN CONTAINERS; PREVENT FROM SPREADING OUT DRAINAGE HOLES OR OVER THE TOP.

Control: (1) (difficult); (2); (6); (11).

Indian Strawberry (Duchesnea indica) From India, this shade-tolerant ground cover spreads by fruit and runners.

Control: (1), taking care to remove each crown; (6).


Invasive Wetland Plants

 

A number of ornamental plants once recommended for water gardens or moist garden soil have spread to our riverbanks, floodplains, and wetlands. They are extremely difficult to eradicate once established - up to 10 years of
repeated treatment may be needed to remove purple loosestrife or Phragmites. These plants propagate by seed and by fleshy root parts which break off easily. Both are spread by water, feet (human, animal, bird), and tires, including those of mowers. They are also found in dredge spoil, fill dirt, and compost. It is not clear whether seeds may be transported by wind. Do not plant exotic water garden plants unless they are not hardy, and never dump plants from fish tanks or water gardens into toilets, storm drains, lakes, or streams.

Common Reed (Phragmites australis, formerly P. communis) Looks like a tall ornamental grass with lovely plumes, usually white or tan. Although the species is indigenous, a particularly aggressive strain, probably introduced or a hybrid, has escaped from natural controls and taken over many formerly diverse wetlands. It is also seen in roadside ditches.

Control: (10) or (11), using Rodeo when the plant is flowering. If possible, follow up with a controlled burn of the dead plants, to allow native plants to return. Do not dig Phragmites - the roots will break, re-sprout, and spread. If herbicide cannot be used, cut annually in late July to reduce spread. 

Giant Reed (Arundo donax) Chokes waterways from Virginia south. It can grow 20' tall.

Control: Same as for Phragmites or mow several times a season.

Japanese Knotweed, Mexican Bamboo (Polygonum cuspidatum) Can grow in shade. The stems have knotty joints, reminiscent of bamboo. It grows 6-10' tall and has large pointed oval or triangular leaves.

Control: Cut at least 3 times each growing season and/or treat with Rodeo (10) or (11). In gardens, heavy mulch or dense shade may kill it.

Purple Loosestrife (Lythrum salicaria, L. virgatum) A handsome garden plant, has tall spikes of magenta flowers over a long bloom season. Often marketed as sterile, it is at best self-sterile, i.e., it can be pollinated by plants you may not be aware of, growing nearby. A single plant can produce up to a million seeds. Like Phragmites, it chokes out all competitors and has taken over millions of acres of wetland in the US.

Control: Initial infestations may be hand-pulled (1) before flowering (DO NOT DIG). Bag and burn or send to the landfill. Otherwise, use Rodeo (10) or (11) when plants begin to bloom (they continue to flower while setting seed). Expect to re-treat for several years until the seed bank is exhausted.

Lesser Celandine, Cenlandine Buttercup (Ranunculus ficaria) has spread from gardens to carpet our floodplains with small yellow flowers in spring. It comes up in winter, giving it a head start over most native spring
wildflowers.

Control: It is not yet known whether digging is effective - the small reproductive corms break off very easily. Try digging (1) before the plants flower. Otherwise, use Rodeo (10 or 11), preferably in February to protect native plants, frogs, and salamanders which become active in March.

 


Invasive, Non-Native Vines

All of these vines shade out the shrubs and young trees of the forest understory, eventually killing them, and changing the open structure of the forest into a dense tangle.

Do not plant next to open space.

Kudzu (Pueraria lobata) The vine that smothered the South is now spreading through the Northeast and Midwest. It has large lobed leaves in groups of three, thick stems, flowers that resemble wisteria, and hairy, bean-like seedpods in fall. It grows extremely rapidly both above and below ground, and can pull down trees.

Control: Small patches may be eliminated by repeated weeding (1), mowing (2), or grazing; established infestations can only be controlled with herbicide (10) or (11). Expect re-growth, but wait a full year and re-treat in the third year. Herbicide is most effective in early fall. Controlled burning (4) of the dead plants the following spring allows native vegetation to return.

Japanese Honeysuckle (Lonicera japonica) Including Hall's Honeysuckle, has gold-and-white flowers with a heavenly scent and sweet nectar in June. This is probably the familiar honeysuckle of your childhood. It is a rampant grower that spirals around trees, often strangling them.

Control: (1); (3); (10); (11) in fall or early spring when native vegetation is dormant. Plan to re-treat repeatedly.

Wisteria, Chinese and Japanese (Wisteria sinensisW. floribunda) Both become heavy, woody vines that can pull down a large tree.

Control: (1); cut back and deadhead ornamental plants (2); (10).

Oriental Bittersweet (Celastrus orbiculatus) Has almost completely displaced American Bittersweet (C. scandens). The Asian plant has its flowers and bright orange seed capsules in clusters all along the stem, while the native species bears them only at the branch tips.

Control: (1); keep ornamental plants cut back, remove all fruits as soon as they open, and bag or burn fruits; to eradicate use Garlon 3a (10).

Porcelain Berry (Ampelopsis brevipedunculata) Has small, hard fruits in a loose, flat cluster that turn from white to yellow, lilac, green, and finally a beautiful turquoise blue.

Control: (1) before fruits appear; keep ornamental plants cut back, and bag or burn fruits before they ripen; to eradicate use Garlon 3a (10).

Englih Ivy (Hedera helix) Grows up trees and can eventually pull them down. It spreads along the ground and occasionally by fruits.

Control: Clip off flowers or fruits if any are seen (2), and (1) pull any seedlings. To eradicate ivy climbing trees, cut stems as high above ground as you can reach, then pull down and paint lower portion of stems and foliage with Garlon 3a (10), taking care not to wet the tree bark. Ground cover: pull up as much as you can, dig out the roots as well as you can, and repeat until it no longer re-sprouts; or treat re-growth with Garlon 3a.

Wintercreeper (Euonymus fortunei).

Control: Same as for English Ivy, but Garlon is not effective; glyphosate mixed with extra sticker-spreader may be.

Vinca, Periwinkle  (Vinca minor).

Control: With persistence, you can dig out Vinca (1); plan to remove re-growth. If digging is not feasible, cut to the ground and treat re-growth with glyphosate (11).


Invasive, Non-Native Shrubs

Multiflora Rose (Rosa multiflora) Formerly recommended for erosion control, hedges, and wildlife habitat, becomes a huge shrub that chokes out all other vegetation and is too dense for many species of birds to nest in, though a few favor it. In shade, it grows up trees like a vine. It is covered with white flowers in June (our native roses have fewer flowers, mostly pink). Distinguish multiflora by its size, and by the presence of very hard, curved thorns, and a fringed edge to the leaf stalk.

Control: (1) pull seedlings, dig out larger plants at least 6" from the crown and 6" down; (4) on extensive infestations; (10) or (11). It may remain green in winter, so herbicide may applied when other plants are dormant. For foliar application, mix Rodeo with extra sticker-spreader, or use Roundup Sure Shot Foam on small plants.

Bush Honeysuckles (Lonicera spp.) Including Amur, Bell's, Morrow's, and Tatarian Honeysuckle. (In our region, assume that any Honeysuckle is exotic unless it is a scarlet-flowered vine). Bush Honeysuckles create denser shade than native shrubs, reducing plant diversity and eliminating nest sites for many forest interior species.

Control: (2) on ornamentals; (1); on shady sites only, brush cut in early spring and again in early fall (3); (4) during the growing season; (7); or (10) late in the growing season.

Japanese Spiraea (Spiraea japonica)

Control: (1); (2); (3), (7), (10), or (11).

Privet (all Ligustrum species).

Control: (1); (7) or (10); or trim off all flowers. Do not cut back or mow.

Burning Bush, Winged Euonymus, Winged Wahoo (Euonymus alatus) Identified by wide, corky wings on the branches. [There is another species called burning bush, E. atropurpureus, which is indigenous to the Appalachians, and a piedmont euonymus called strawberry bush (E. americanus).]

Control: (1); (7) or (10); or trim off all flowers.

Japanese Barberry (Berberis thunbergii) Red and green varieties.

Control: (1); (7) or (10); or trim off all flowers.


Small to Medium Invasive, Non-Native Trees

Empress Tree, Princess Tree (Paulownia tomentosa) Large panicles of lavender flowers, like upside-down wisteria, identify this tree in spring; the large brown seed capsules remain all year. The leaves are very large and heart-shaped. Winged seeds allow it to spread deep into undeveloped areas, though it needs some sunlight and is most common along trails and waterways. It grows very rapidly and sprouts readily from roots and cut stumps.

Control: (1) - seedlings and small saplings only; (7), (8), (9), or (10) - use 50% solution, anytime the ground is not frozen; (11) on re-growth and small trees.

Mimosa (Albizia julibrissin) Has rather garish pink flowers in summer and feathery compound leaves. It spreads slowly by wind-borne seedpods, or in water or fill-dirt. It re-sprouts when cut or burned. Needs some sunlight.

Control: (1); (7), (8), (9), or (10).

Siberian Elm (Ulmus pumila) A fast-growing medium-height tree also sold for hedges, displaces our native elms, which are already under pressure from Dutch elm disease. It forms dense thickets under which nothing else grows. Its small oval leaves have a single tooth.

Control: (1); (7), (8), (9), or (10).

Russian Olive, Autumn Olive (Eleagnus angustifolium, E. umbellata) Formerly recommended for erosion control and wildlife value, these have proved highly invasive and diminish the overall quality of wildlife habitat.

Control: (1) - up to 4" diameter trunks; (7) or (10) or bury stump. Do not mow or burn.


Flowering Invasive, Non-Native Fruit Trees

These displace our native fruit trees:

Cherry, edible and ornamental (Prunus avium, P. cerasus, Japanese species and hybrids).

Pear, Bradford and other ornamental pears (Pyrus calleryana) Self-sterile but can pollinate other cultivars, now spreading rapidly from street plantings.

White Mulberry (Morus alba) The fruits may be white, purple, or black; leaves are lobed. Our delicious native red mulberry, which has very large, usually unlobed leaves, is dying out from a root disease carried by white mulberry.

Control of flowering/fruit trees: (1; (7) or (10); (8) if very large; or if grown for harvest, protect fruit from birds with netting or hardware cloth.


Medium to Tall Non-Native Invasive Trees

Norway Maple (Acer platanoides) Has large leaves similar to sugar maple. Break a leaf or stalk—a drop of white sap will show if it is Norway maple. Fall foliage is yellow. (Exception: cultivars such as 'Crimson King,' which have red leaves in spring or summer, may have red autumn leaves.) The leaves turn color late, usually in November. This tree suppresses growth of grass, garden plants, and forest understory beneath it, at least as far as the drip-line. Its wind-borne seeds can germinate and grow in deep shade. The presence of young Norway maples in our woodlands is increasing. Our mixed deciduous forests will give way to pure stands of Norway maple in the next century unless we control its spread now.

Control: (1); (7), (8), (9), or (10); (11) in mid-October to early November, before the leaves turn color.

Tree of Heaven (Ailanthus altissima) Known from A Tree Grows in Brooklyn, is incredibly tough and can grow in the poorest conditions. It produces huge quantities of wind-borne seeds, grows rapidly, and secretes a toxin that kills other plants. Its long compound leaves, with 11-25 lance-shaped leaflets, smell like peanut butter or burnt coffee when crushed. Once established, this tree cannot be removed by mechanical means alone.

Control: (1) Seedlings only. Herbicide - use Garlon 3a (9) with no more than a 1" gap between cuts, or (10); plus (11) on re-growth. Or paint bottom 12" of bark with Garlon 4 (in February or March to protect surrounding plants). USE MAXIMUM STRENGTH SPECIFIED ON LABEL for all herbicide applications on Ailanthus. Glyphosate is not effective against Ailanthus.

Sawtooth Oak (Quercus acutissima) Has oval leaves with sawtooth edges and huge acorns. Often recommended for wildlife, this Asian tree has spread into our region from forestry plantings, displacing indigenous forest trees.

Control: (1); (7), (8), (9), or (10); (11) on small trees and re-growth.