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Invasives of concern to the Poconos

From an extensive list of introduced plant species, a number are listed by state and federal agencies as invasive and/or noxious as a consequence to becoming a hazard to ecosystems, agriculture and in some cases, human health.

A number of species are of particular concern because of infestations in northeastern counties of Pennsylvania, and are well documented elsewhere (including effective means of control and eradication). A public service site offers many images to assist in identification.

Invasives that arrived inadvertantly or for non-horticultural use, or have escaped from cultivation, commonly share traits of having few natural predators (primarily insects and herbivores). They often have textures and tastes disliked by herbivores or are chemically "invisible" to insects that normally keep plant populations in check; in fact, introduced exotics are sometimes promoted as being "pest resistant."

Although these species are becoming illegal for commercial sale, they often remain traded among friends, especially if they are deer resistant. Species listed as "others" are reported outside of Carbon, Monroe, Pike and Wayne Counties but still may yet arrive through a variety of means - hence, there is no need in compounding the problem by bringing them in.

Herbaceous Plants

Aegopodium podagraria

Goutweed, aka bishop's weed, snow-on-the-mountain - Commonly planted in the past and escaped; spreads aggressively by roots to form dense patches, displace native species, and greatly reduce species diversity in the ground layer. Goutweed patches inhibit the establishment of conifers and other native tree species as well.

Alliaria petiolata

Garlic mustard - Invasive in many states; spreading aggressively in woodlands by seed. Once introduced to an area, garlic mustard outcompetes native plants by aggressively monopolizing light, moisture, nutrients, soil and space. Wildlife species that depend on these early plants for their foliage, pollen, nectar, fruits, seeds and roots are deprived of these essential food sources when garlic mustard replaces them.

Cirsium arvense

Canada thistle - PA noxious weed and in 42 other states. Canada thistle grows in barrens, glades, meadows, prairies, fields, pastures, and waste places. As it establishes itself in an area, Canada thistle crowds out and replaces native plants, changes the structure and species composition of natural plant communities and reduces plant and animal diversity. This highly invasive thistle prevents the coexistence of other plant species through shading, competition for soil resources and possibly through the release of chemical toxins poisonous to other plants.

Cirsium vulgare

Bull thistle - PA noxious weed. Bull thistle can invade almost any type of disturbed area, such as forest clearcuts, riparian areas and pastures. Plants can form dense thickets, displacing other vegetation.

Hesperis matronalis

Dame's rocket - Planted in gardens; escaped and naturalized along roads; spreads by seed. It is still being used as a landscape plant and has become so common that many, mistakenly, believe that it is a native wildflower. Although it is not a large-scale invasive, dame's rocket can dominate moist areas of meadow, forest edge and alluvial woods to the exclusion of native plants.

Lythrum salicaria, L. virgatum

Purple loosestife - Garden escape which has become invasive in many states; PA noxious weed. Purple loosestrife adapts readily to natural and disturbed wetlands. As it establishes and expands, it outcompetes and replaces native grasses, sedges, and other flowering plants that provide a higher quality source of nutrition for wildlife. The highly invasive nature of purple loosestrife allows it to form dense, homogeneous stands that restrict native wetland plant species, including some federally endangered orchids, and reduce habitat for waterfowl.

Myriophyllum spicatum

Eurasian water-milfoil - An emergent, herbaceous aquatic plant that forms large, floating mats of vegetation on the surface of lakes, rivers, and other water bodies, preventing light penetration for native aquatic plants and impeding water traffic. Eurasian watermilfoil tends to invade disturbed areas where native plants cannot adapt to the alteration. It does not spread rapidly into undisturbed areas where native plants are well established.

Ornithogalum umbellatum

Star-of-Bethlehem - Common garden plant which has widely escaped. Since this plant is still being used horticulturally, it is likely to continue spreading beyond its current range. Ornithogalum umbellatum is poisonous if not lethal to livestock and should be prevented from spreading into agricultural situations. Ornithogalum umbellatum produces new bulbs each year, and these bulbs are readily moved downstream to new localities. It has the ability to form locally dense stands along the edges of the rivers and streams, allowing it to crowd out native riparian plants.

Pastinaca sativa

Wild parsnip - Found commonly along roadsides; widespread and abundant; spread by seed. Well-established prairies are not likely to be invaded by parsnip, but it can become quite abundant on prairie edges and in disturbed patches within otherwise high-quality prairies. Once established at the edges, parsnip can spread into adjacent high-quality areas.

Polygonum cuspidatum

Japanese knotweed (AKA Fallopia japonica) and giant knotweed (Polygonum sachalinense) are herbaceous perennials that form large colonies of erect stems that can reach 9 feet in height. They spread by vigorous rhizomes (horizontal stems that grow just below the soil surface). Japanese knotweed and giant knotweed are very similar in appearance and are known to hybridize. It is most commonly found lining the banks of creeks and rivers where it often forms an impenetrable wall of stems; it also occurs in wetlands, waste ground, and along roads and railroads. Dense stands of knotweed exclude other plant species leading to very limited biological diversity in infested sites.

Trapa natans

Water chestnut - Wetland plant; should not be introduced as it will escape, spread, and naturalize. Plants grow in quiet streams, ponds, freshwater regions of estuaries, and on exposed mud flats. One acre of water chestnut can produce enough seeds to cover 100 acres the following year. Each seed can give rise to 10-15 rosettes, and each rosette may produce as many as 20 seeds. Seeds have been known to remain viable for up to 12 years. The fruits may be dispersed when individual plants are uprooted and float downstream.

Grasses

Bromus tectorum

Cheatgrass - Annual grass; on the noxious weed lists of at least 35 states. Bromus tectorum has the ability to draw down soil moisture and nutrients to very low levels, making it difficult for other species to compete. Due to its tendency to mature early and then dry out, it gains a competitive advantage through the promotion of fire. An increased cycle of fires favors annual species at the expense of many perennials.

Microstegium vimineum

Japanese stilt grass - Annual grass; invasive in many states; spreading through woodlands by seed, especially in Monroe and Pike Counties. Stilt grass occurs in a wide variety of habitats and readily invades areas subject to regular mowing, tilling, foot traffic, and other soil disturbing activities. It threatens native plants and natural habitats in open to shady, and moist to dry locations. Stilt grass spreads to form extensive patches, displacing native species that are not able to compete with it.

Phalaris arundinacea

Reed canary grass - Aggressive wetland grass; native and introduced strains; widespread and abundant. Reed canary-grass forms dense, monospecific stands in open wetlands, wet meadows, riparian areas, and shores. It effectively excludes all other plant species, causing greatly decreased biological diversity in wetland communities.

Phragmites australis

Common reed - a tall, perennial grass that can grow to over 15 feet in height found in tidal and nontidal brackish and freshwater marshes, river edges, shores of lakes and ponds, roadsides and disturbed areas. Once introduced Phragmites invades a site it quickly can take over a marsh community, crowding out native plants, changing marsh hydrology, altering wildlife habitat, and increasing fire potential. Its high biomass blocks light to other plants and occupies all the growing space below ground

Shrubs

Berberis thunbergii and Berberis vulgaris

Japanese barberry (B. thunbergii) and European barberry (B. vulgaris) - Escaped from cultivation and invasive in many states; spread by birds. Shade tolerant, drought resistant, and adaptable, barberry forms dense stands in natural habitats including canopy forests, open woodlands, wetlands, pastures, and meadows and alters soil pH, nitrogen levels, and biological activity in the soil. Once established, barberry displaces native plants and reduces wildlife habitat and forage.

Euonymus alatus

Winged Euonymus or Burning Bush - Escaped from plantings; invasive in moist forests. Winged euonymus is a threat to mature forests and successional fields and woodlands because it creates dense thickets that can shade out native herbs and shrubs.

Lonicera morrowii

Morrow's honeysuckle - Escaped from plantings and invasive in many states; seeds spread by birds. Native bush honeysuckles may be confused with these exotic species and cultivars. Unlike the exotics, most of native bush honeysuckles have solid stems. Morrow's honeysuckle is capable of invading bogs, fens, lakeshores, sandplains and other uncommon habitat types, forming a dense shrub layer that crowds and shades out native plant species. They alter habitats by decreasing light availability, by depleting soil moisture and nutrients, and possibly by releasing toxic chemicals that prevent other plant species from growing in the vicinity.

Rosa multiflora

Multiflora rose - Invasive in many states; seeds spread by birds; PA noxious weed. Multiflora rose is extremely prolific and can form impenetrable thickets that exclude native plant species. This exotic rose readily invades open woodlands, forest edges, successional fields, savannas and prairies that have been subjected to land disturbance.

Spiraea japonica

Japanese spiraea - Frequently planted; escaped in some areas. Japanese spiraea can rapidly take over disturbed areas. Growing populations creep into meadows, forest openings, and other sites. Once established, spiraea grows rapidly and forms dense stands that outcompete much of the existing native herbs and shrubs. Seeds of Japanese spiraea last for many years in the soil, making its control and the restoration of native vegetation especially difficult.

Viburnum opulus var. opulus

Guelder rose - Guelder rose and native highbush cranberry (Viburnum opulus var. americanum) are varieties of the same shrub species, and distinguishing between them can be difficult. Guelder rose usually can be identified by the large saucer - shaped glands on the leafstalk. Guelder rose is a cause for concern when it grows in natural areas and uncommon natural habitats, including fens, where it may displace native plants and its reported ability to interbreed with the native highbush cranberry could produce a truly invasive shrub.

Trees

Acer platanoides

Norway maple - a frequent invader of urban and suburban forests. Its extreme shade tolerance, especially when young, has allowed it to penetrate beneath an intact forest canopy. Forests invaded by Norway maple suffer losses in diversity of native forest wildflowers compared with forests in which the canopy is dominated by native species such as sugar maple. This is at least in part due to the dense shade cast by Norway maples, and the shallow roots, which compete with other vegetation.

Ailanthus altissima

Tree-of-heaven - Invasive in many states; wind spreads prolific seeds. Tree-of-heaven is a prolific seed producer, grows rapidly, and can overrun native vegetation. Once established, it can quickly take over a site and form an impenetrable thicket. Ailanthus trees also produces toxins that prevent the establishment of other plant species. The root system is aggressive enough to cause damage to sewers and foundations.

Vines

Celastrus orbiculatus

Oriental bittersweet - Escaped from cultivation and invasive in many states; spreading rapidly (by birds). Oriental bittersweet is a deciduous, woody, perennial vine and an aggressive invader that threatens all vegetation levels of forested and open areas. It grows over other vegetation, completely covering it, and kills other plants by preventing photosynthesis, girdling, and uprooting by force of its massive weight.

Lonicera japonica

Japanese honeysuckle - Invasive in many states, Japanese honeysuckle is a perennial vine that climbs by twisting its stems around vertical structures, including limbs and trunks of shrubs and small trees. The vines cut off the flow of water through the plant and kill it. Dense growths of honeysuckle covering vegetation can also gradually kill plants by blocking sunlight from reaching their leaves. Vigorous root competition also helps Japanese honeysuckle spread and displace neighboring native vegetation.

Polygonum perfoliatum

Mile-a-minute vine - a PA Noxious Weed, Mile-a-minute weed, also known as Devil's tail tearthumb, is an herbaceous, annual, trailing vine. Mile-a-minute weed grows rapidly, scrambling over shrubs and other vegetation, blocking the foliage of covered plants from available light, and reducing their ability to photosynthesize, which stresses, weakens and kills them. Large infestations of mile-a-minute weed eventually reduce native plant species in natural areas.

Other species listed as invasive in Pennsylvania

Carduus nutans (Musk thistle) - PA noxious Weed

Galega officinalis (Goatsrue) - PA and Federal Noxious Weed

Heracleum mantegazzianum (Giant hogweed) - PA and Federal Noxious Weed

Perilla frutescens (Beefsteak plant) - Garden escape; widespread mostly along roadsides; spread by seed

Ranunculus ficaria (Lesser celandine) - Spreads by roots and shoots; can be very aggressive in wetlands

Miscanthus sinensis (Maiden grass) - Commonly planted ornamental grass which can escape and spread by seed

Sorghum bicolor ssp. drummondii (Shattercane) - PA noxious Weed

Sorghum halepense (Johnson grass) PA noxious Weed; spreads by roots and seeds

Elaeagnus angustifolia (Russian olive) - Escaped from plantings and invasive in many states; spread by birds

Elaeagnus umbellata (Autumn olive) - Escaped from plantings and invasive in many states; rapidly spread by birds

Ligustrum obtusifolium (Border privet) - Escaped from cultivation; seeds spread by birds

Ligustrum vulgare (Common privet) - Planted very commonly in the past and escaped; invasive in many states

Lonicera maackii (Amur honeysuckle) - Escaped from plantings; seeds spread by birds

Lonicera morrowii x tatarica (Bell's honeysuckle) - Escaped from cultivation

Lonicera standishii (Standish honeysuckle) - Escaped from plantings; seeds spread by birds

Lonicera tatarica (Tartarian honeysuckle) - Escaped from plantings; seeds spread by birds

Rhamnus cathartica (Common buckthorn) - Becoming a problem in PA

Rhamnus frangula (Glossy buckthorn) - Becoming a problem in PA

Rubus phoenicolasius (Wineberry) - Common bramble; not cultivated; spread by seed

Acer pseudoplatanus (Sycamore maple) - Escaped from cultivation; wind spreads prolific seeds

Paulownia tomentosa (Princess tree) - Prolific seeds fall to start new seedlings south

Pyrus calleryana (Callery pear) - Commonly planted street tree; becoming a problem as an escape

Ulmus pumila (Siberian elm) - Escaped from cultivation

Akebia quinata (Fiveleaf akebia) - Escaped from cultivation south

Ampelopsis brevipedunculata (Porcelain-berry) - Escaped from cultivation

Pueraria lobata (Kudzu) - Invasive in many states; PA Noxious Weed