Invasive Species Information :: Norwalk River Watershed Association

Invasive Species Information

The following plants are invasive species (or are potentially invasive) within the Norwalk River watershed. They crowd out the region's traditional plantlife, converting a healthy diversity of species into an unhealthy monoculture. These plants are to be avoided, managed, or removed throughout the watershed. (This list was compiled June 1998).

TREES
Norway Maple Acer platanoides
Sycamore Maple Acer pseudoplatanus
Tree-of-heaven Ailanthus altissima
White Mulberry Morus alba
Empress-tree Paulownia tomentosa
Amur Cork Tree Phellodendron japonicum
White or Poplar Cottonwood Populus alba
Black Locust Robinia pseudoacacia

SHRUBS
Japanese Barberry Berberis thunbergii
Russian Olive Elaeagnus angustifolia
Autumn Olive Elaeagnus umbellata
Winged Euonymus Euonymus alatus
Amur Honeysuckle Lonicera maackii
Morrow's Honeysuckle Lonicera morrowii
Tartarian Honeysuckle Lonicera tatarica
Blunt-leaved Privet Ligustrum obtusifolium
Common or European Privet Ligustrum vulgare
Wineberry Rubus phoenicolasias
Common or Smooth Buckthorn Rhamnus cathartica
Glossy or Shining Buckhorn Rhamnus frangula
Multiflora Rose Rosa multiflora
Japanese Rose Rosa rugosa

VINES
Porcelain Berry Ampelopsis brevipedunculata
Asiatic Bittersweet Celastrus orbiculatus
Japanese Honeysuckle Lonicera japonica
Mile-a-Minute Vine Polygonum perfoliatum
Kudzu Pueraria lobata

HERBACEOUS PLANTS
Purple Loosestrife Lythrum salicaria
Garden Loosestrife Lysimachia vulgaris
Japanpese Knotweed Polygonum cuspidatum
Yellow Flag Iris Iris pseudacorus
Common Reed Phragmites australis
Garlic Mustard Alliaria petiolata
Japanese Stilt Grass Microstegium vimineum
Leafy Spurge Euphorbia esula
European Water-milfoil Myriophyllum spicatum
Cottonweed Froelichia gracilis
Goutweed Aegopodium podagraria
Black Swallow-wort Vincetoxicum nigrum
White Swallow-wort Vincetoxicum hirundinaria

Invasive Beetle Alert!

The newest threat to trees and forests is the Asian Longhorned Beetle (Anaplophora glabripennis).

With a preference for maples (sugar, Norway, red, silver, and sycamore), it also attacks horse-chestnuts, black locust, elms, birches, willows, poplars, and green ash. The only known method of controlling it is to cut down the infested tree and chip or burn all the wood. Early detection and swift action may prevent the spread of these beetles which came into the US and NY in solid packing crates from China and which have done serious damage to trees in central Park and elsewhere. So look for these signs.

The adult female digs or chews out a cup or niche in the bark for each of the 30-70 eggs she lays in the spring. These hatch in 10-15 days, and the larvae burrow into the tree - often making the tree ooze sap and creating piles of sawdust in the crotch of branches or at the base of the trunk. Tunneling girdles the branches and over time leads to dieback and the death of the tree. After pupating, the emerging adults burrow out -leaving an almost perfectly round exit hole about 1/2" in diameter.

Adult beetles are 3/4-1 1/4" long, black with white spots on the back, with black-and-white bands on long antennae, and blueish feet. They are most evident May through October. If you discover them, call your local Tree Warden and the Cooperative Extension System (203-974-8474). For more information, access: http://www. aphis.usda.gov/oa/alb/alb.html.

Mile-a-Minute Vine Alert!

Polygonum perfoliatum, the Kudzu of the north, grows 6" a day, prefers sunlight, has stalks with prickers that stick to other plants and form dense, smothering mats. It has both triangular and round leaves and purple berries. Control this new invasive threat by mowing or hand-pulling the plant before seed sets. Put the plants in a black plastic garbage bag in the sun and let them thoroughly heat and rot. Wear leather gloves and long sleeves when you're on the attack!. For more information log onto www.eeb.uconn.edu to learn more about this and other invasive species that need everyone's attention if our native plants are to survive. Unlike established wetland invasives, such as purple loosestrife, we may be able to stop this one on its race east from Greenwich and New York State.

Pervasive Invasive: Japanese Barberry

Japanese barberry (berberis thunbergii ) is one of the most hardy, pervasive invasive plants. It has no known predators (deer don't browse it), berries are easily spread by water or birds, and it will grow almost anywhere in varied soil conditions and even in very minimal light. It is the most pervasive shrub of woodlands and old fields and outcompetes native flora for sun, water, and nutrients. One study even showed that it produces a chemical that discourages earthworms and thereby hinders enrichment of the soil. Yet it is one of the easiest invasive plants to recognize and remove, and awareness of it in the landscape may lead the enlightened viewer to identify and eliminate two other pervasive invasives: multiflora rose and winged euonymus.

Japanese barberry is easily recognized in every season. The compact woody shrub grows 2-6" high and has a short vaselike form. Its slender, arching stems have untoothed leaves with a single thorn below each leaf cluster. Its leaves turn a deep, orange-red in the fall. Red oblong 1/2" berries are born singly or in clusters along the stem. Its bisexual flowers are pale yellow. Inner bark and roots are a vibrant deep yellow. Typical of alien plants, it leafs out earlier than other plants in the spring, and its leaves stay on later in the fall.

Physical removal - by long-handled shovel, mattock, or Weed Wrench (for the toughest, largest plants or those wedged between roots or in a stone wall) - is the proven and chosen method of eradication. The most stubborn plants can be cut off low on the stem and treated with Roundup™, but be careful not to let this nonselective systemic herbicide contact water or other desirable vegetation. Before digging the plant, its berries should be removed and packaged in a ziplock bag, that later can be thrown out with the garbage. When dug, the bushes should be shaken to remove excess soil and then upended to provide shelter for wildlife while the roots dry out and die. The hole where the plant was removed should be filled, tamped down, and covered with leaves to prevent other invasive seeds from entering the disturbed soil. The resulting natural-looking terrain will be attractive and encouraging.

Leather work gloves and a tough work clothing should be worn to minimize pricks during the elimination process.

Spring is a good time to attack plants on higher, drier ground for better footing and fewer insects. Fall is a better time to attend to the previously wet areas. Target areas along streams or trails first to minimize future seed dispersal by water or birds.

Check up on the areas where you've worked for the next few years. Any emerging barberry should be small and quite easy to pull up by hand.

Two great new sources of information on invasive plants:

Invasive of the Month Really helpful information and pictures for identification and control.
Invasive Plants in Winter In the menu in Need to Identify pull-down menu: click on Invasive Plants in Winter; then Hot to Choose a View, click on Browse – Show ALL; then hit the “Start the ID!”