Exotic and Invasive Species

• 2005 Chequamegon-Nicolet Invasive Plant Control Project
• 2007 Supplement to the Non-Native Invasive Plant Environmental Assessment
• 2009 Supplement to the Non-Native Invasive Plant Environmental Assessment
• 2011 Supplement to the Non-Native Invasive Plant Environmental Assessment
• 2014 Administrative Change to the 2005 Chequamegon-Nicolet Invasive Plant Control Project

Native Range: Eurasia (Japan, China, Korea, Manchuria, Turkey and southern Russia)

Description: Exotic bush honeysuckles are upright, generally deciduous shrubs that range from 6 to 15 feet in height. The 1-2 ½ inch, egg-shaped leaves are opposite along the stem and short-stalked. Older stems are often hollow. Pairs of fragrant, tubular flowers less than an inch long are borne along the stem in the leaf axils. Flower color varies from creamy white to pink or crimson in some varieties of Tartarian honeysuckle. Flowering generally occurs from early to late spring, but varies for each species and cultivar. The fruits are red to orange, many-seeded berries. Native bush honeysuckles may be confused with these exotic species and cultivars, so proper identification is necessary. Unlike the exotics, most of our native bush honeysuckles have solid stems.

Ecological Threat: Exotic bush honeysuckles can rapidly invade and overtake a site, 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. Exotic bush honeysuckles may compete with native bush honeysuckles for pollinators, resulting in reduced seed set for native species. In addition, the fruits of exotic bush honeysuckles, while abundant and rich in carbohydrates, do not offer migrating birds the high-fat, nutrient-rich food sources needed for long flights, that are supplied by native plant species.

Distribution in the United States: Amur, Tartarian, Morrow's, and pretty honeysuckle generally range from the central Great Plains to southern New England and south to Tennessee and North Carolina. The remaining species are sporadically distributed. Click here to see a distribution map.

Habitat in the United States: Exotic bush honeysuckles are relatively shade-intolerant and most often occur in forest edge, abandoned field, pasture, roadsides and other open, upland habitats. Woodlands, especially those that have been grazed or otherwise disturbed, may also be invaded by exotic bush honeysuckles. Morrow's honeysuckle and pretty honeysuckle have the greatest habitat breadth and are capable of invading bogs, fens, lakeshores, sandplains and other uncommon habitat types.

Background: Exotic bush honeysuckles have been introduced for use as ornamentals, for wildlife cover and for soil erosion control. 

Methods of Reproduction and Dispersal: Open-grown exotic bush honeysuckles fruit prolifically and are highly attractive to birds. In the eastern United States, over twenty species of birds feed on the persistent fruits and widely disseminate seeds across the landscape. In established populations, vegetative sprouting also aids in the persistence of these exotic shrubs.

Current Management Approaches: Mechanical and chemical methods are the primary means of control of exotic bush honeysuckles. No biological control agents are currently available for these plants and any potential agents that might be considered would have to be specific to the exotic species, for obvious reasons. Hand removal of seedlings or small plants may be useful for light infestations, but care should be taken not to disturb the soil any more than necessary. In shaded forest habitats, where exotic bush honeysuckles tend to be less resilient, repeated clippings to ground level, during the growing season, may result in high mortality. Clipping must be repeated at least once yearly because bush honeysuckles that are cut once and left to grow will often form stands that are more dense and productive than they were prior to cutting.

Seedlings of exotic bush honeysuckles can also be controlled by application of a systemic herbicide, like glyphosate (e.g., Roundup), at a 1 percent solution, sprayed onto the foliage or applied by sponge. Well established stands of exotic bush honeysuckles are probably best managed by cutting the stems to ground level and painting or spraying the stumps with a slightly higher rate of glyphosate (2-3%).

Prescribed burning has shown some promise for exotic bush honeysuckles growing in open habitats. In all instances, control should be initiated prior to the seed dispersal period (late summer to early autumn) to minimize reinvasion of treated habitats.

Description: Native to Asia autumn olive is a medium to large shrub, reaching heights of 20 feet. The leaves, are alternate on the stems, are generally oval in shape, approximately 1-3 inches (2.5-7.5 cm) long, and have a smooth margin. The upper surface of leaves is dark green to grayish-green, and the lower surface is covered with silvery white scales, a conspicuous characteristic that can be seen from a distance. The small light yellow flowers bloom in late April and May after the first leaves have appeared. Flowers and fruits, when present, are borne along twigs. The small (less than 1/4 inch) fleshy fruits range in color from pink to red and are produced in abundance each year. This species is similar to Russian olive but the leaves of Russian olive are longer and more narrow, and are much more silvery in appearance.

Habitat and Distribution: Autumn olive has nitrogen-fixing root nodules which allow it to thrive in poor soils, such as abandoned fields, pastures, and roadsides. It is rarely encountered in dense forests or on very wet sites. In the eastern and central United States, autumn olive has been planted primarily to provide food and cover for wildlife but also as screens and barriers along highways, to stabilize and revegetate road banks, and to reclaim mine spoil. It has since escaped cultivation and become naturalized in much of the northeast.

Reproduction and Dispersal: Autumn olive seeds are dispersed by birds over long distances. It also reproduces vegetatively when cut or burned.

Ecological Threat: In addition to its prolific fruiting, seed dispersal by birds, rapid growth and ability to thrive in poor soils, autumn olive resprouts vigorously after cutting or burning. It creates heavy shade which suppresses plants that require direct sunlight.

References

Virginia Natural Heritage Program

Illinois Nature Preserves Commission

Description: Bull thistle is a biennial with prickly, winged stems. The leaves are coarse and spiny above with wooly white hairs below. A purple "brush" of flowers emerges from a spiny green ovoid base.

European marsh thistle is also invasive in Wisconsin and looks similar to bull thistle. Also note that several native thistles exist in prairies that may be confused with exotic species. Verify identification before initiating control work. The native species tend to have leaves that are white and wooly beneath or the flower heads are gummy/sticky. The non-native thistles tend to have very prickly stems and leaves.

Distribution and Habitat: Bull thistle was introduced from southern Europe and western Asia. It occurs throughout Wisconsin in disturbed areas such as pastures, roadsides, waste areas, and ditch banks and is a problem in prairies, old fields, and hay fields.

Life History: Bull thistle is a biennial and grows from a flat rosette of leaves the first year. Seedlings emerge from early spring to late fall, and the length of time to flowering can vary from 4 months to 22 months. A single taproot is formed. Reproduction is by seed.

Stem elongation takes place in early May. Blooming starts with the terminal head in early June and continues until mid-August with the lower branches. Seeds mature and may disperse within 7 to 10 days of flowering. The bulk of seed is produced on the upper branches, and germination may run as high as 95%. Wind dispersal allows for movement over long distances. Seeds can remain viable in the soil for over 10 years. Each plant is capable of producing up to 10,000 seeds, which are dispersed by wind.

Ecological Threat: Bull thistle has been known to invade native and restored grasslands despite the presence of dense, native prairie vegetation. Glade communities are also likely areas for thistle establishment. These species are very aggressive in disturbed areas, and can pose a major problem in buffer and restoration areas. Control of these thistles is important before beginning a prairie restoration.

Controlling Exotic Thistles: Control efforts will be long-term since seeds remain viable in the soil for over 10 years.

Mechanical Control: Eliminating seed production is the most effective mechanical control technique. Thistles mowed in bud or early bloom stage will produce new branches from buds in the axils of the basal leaves. However, close mowing or cutting twice per season will usually prevent seed production. This can be done at any time during the growing season, although cutting is easier when the thistles are smaller. Mowing once flowering has begun may result in the spread of viable seeds with the mower. For effective selective control, plants should be cut with a sharp shovel at 1" to 2" below the soil surface before flowering. Competition with native vegetation decreases seedling establishment.

Biological Control: Two exotic weevils, the flower head weevil (Rhinocyllus conicus) and the rosette weevil (Trichosirocalus horridus) have been introduced in several states, and appear to be effective biological control agents that limit populations of musk thistle. However, these insects are not in use in Wisconsin due to the risks presented to rare native thistles.
Chemical Control: Herbicides are not recommended for use on exotic thistles in high quality natural areas. Chemical control is most effective when plants are in the rosette stage and least effective when thistles are flowering. Dicamba, 2,4-D, and clopyralid herbicides are all effective.

References:

WDNR. Wisconsin Department of Natural Resources web page.
Lym, Rodney G. 1996. The thistles of North Dakota. NDSU Extension Service.

Note: Canada Thistle is considered a noxious plant is Wisconsin. Planting it is prohibited by law, and it must be destroyed.

Native Range: Temperate regions of Eurasia

Description: Canada thistle is an herbaceous perennial with erect stems 1½-4 feet tall, prickly leaves and an extensive creeping rootstock. Stems are branched, often slightly hairy, and ridged. Leaves are lance-shaped, irregularly lobed with spiny, toothed margins and are borne singly and alternately along the stem. Rose-purple, lavender, or sometimes white flower heads appear from June through October, generally, and occur in rounded, umbrella-shaped clusters. The small, dry, single-seeded fruits of Canada thistle, called achenes, are 1-1½ inches long and have a feathery structure attached to the seed base. Many native species of thistle occur in the U.S., some of which are rare. Because of the possibility of confusion with native species, Canada thistle should be accurately identified before any control is attempted.

Ecological Threat: Natural communities that are threatened by Canada thistle include non-forested plant communities such as prairies, barrens, savannas, glades, sand dunes, fields and meadows that have been impacted by disturbance. 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. Canada thistle is declared a "noxious weed" throughout the U.S. and has long been recognized as a major agricultural pest, costing tens of millions of dollars in direct crop losses annually and additional millions costs for control. Only recently have the harmful impacts of Canada thistle to native species and natural ecosystems received notable attention.

Distribution in the United States: Canada thistle is distributed throughout the northern U.S., from northern California to Maine and southward to Virginia. It is also found in Canada, for which it was named. Canada thistle has been identified as a management problem on many national parks and on preserves of The Nature Conservancy in the upper Midwest, Plains states, and the Pacific northwest.

Habitat in the United States: Canada thistle grows in barrens, glades, meadows, prairies, fields, pastures, and waste places. It does best in disturbed upland areas but also invades wet areas with fluctuating water levels such as streambank sedge meadows and wet prairies.

Background: Canada thistle was introduced to the United States, probably by accident, in the early 1600s and, by 1954, had been declared a noxious weed in forty-three states. In Canada and the U.S., it is considered one of the most tenacious and economically important agricultural weeds, but only in recent years has it been recognized as a problem in natural areas.

Biology and Spread: Canada thistle produces an abundance of bristly-plumed seeds which are easily dispersed by the wind. Most of the seeds germinate within a year, but some may remain viable in the soil for up to twenty years or more. Vegetative reproduction in Canada thistle is aided by a fibrous taproot capable of sending out lateral roots as deep as 3 feet below ground, and from which shoots sprout up at frequent intervals. It also readily regenerates from root fragments less than an inch in length.

Management Options: Management of Canada thistle can be achieved through hand-cutting, mowing, controlled burning, and chemical means, depending on the level of infestation and the type of area being managed. Due to its perennial nature, entire plants must be killed in order to prevent regrowth from rootstock. Hand-cutting of individual plants or mowing of larger infestations should be conducted prior to seed set and must be repeated until the starch reserves in the roots are exhausted. Because early season burning of Canada thistle can stimulate its growth and flowering, controlled burns should be carried out late in the growing season for best effect. In natural areas where Canada thistle is interspersed with desirable native plants, targeted application of a systemic herbicide such as glyphosate (e.g., Roundup or Rodeo), which carries plant toxins to the roots, may be effective. For extensive infestations in disturbed areas with little desirable vegetation, broad application of this type herbicide may be the most effective method. Repeated applications are usually necessary due to the long life of seeds stored in the soil.

Description: Native to North America, common reed is a tall perennial wetland grass ranging in height from three to 13 feet. Horizontal stems (rhizomes) give rise to annual erect shoots that support broad sheath-like leaves up to 2 feet long. Leaves are arranged alternately along the top half of the stem and are stiff and sharp, due to a high content of cellulose and silica. In mid-summer common reed produces a large, silky inflorescence that grows at the tops of the stems and drape to one side. A typical inflorescence may be one to two feet long, and several inches wide.

Habitat and Distribution: Common reed thrives in sunny wetland habitats. It is commonly found in the moist soil of shallow brackish and freshwater marshes. It also grows along riverbanks and lakeshores, and can form floating mats in deeper waters. This species is prevalent in the disturbed and degraded soils found along roadsides, ditches and dredged areas. High salinity limits its growth. Distribution is widespread throughout the U.S.

Methods of reproduction and Dispersal: Common reed spreads rapidly through prolific seeds and underground root systems called rhizomes. Rhizomes can live for 3 to 6 years and grow horizontally underground for 3 feet or more before rising vertically to become an above-ground shoot. Rhizome fragments are dispersed by water, animals, and construction equipment.

Ecological Threat: Although common reed is a native American plant its invasive characteristics can rapidly replace other desirable vegetation. Invasive stands can quickly replace desirable wetland species such as wild rice, cattails, and native wetland orchids. Monocultures as large as 7,000 acres have been documented.

Description: Eurasian watermilfoil, also called spike watermilfoil, is an emergent, herbaceous aquatic plant in the Water-milfoil family, or Haloragaceae. Stems grow to the water surface, usually extending 3 to 10, but as much as 33, feet in length and frequently forming dense mats. Stems of Eurasian milfoil are long, slender, branching, hairless, and become leafless toward the base. New plants may emerge from each node (joint) on a stem, and root upon contact with mud. The grayish-green leaves of Eurasian watermilfoil are finely divided and occur in whorls of three or four along the stem, with 12-16 pairs of fine, thin leaflets about 12 inches long. These leaflets give milfoil a feathery appearance that is a distinguishing feature of the plant. Eurasian watermilfoil produces small yellow, 4-parted flowers on a spike that projects 2-4 inches above the water surface. The fruit is a hard, segmented capsule containing four seeds.

Ecological Threat: Eurasian milfoil can form 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. The plant thrives in areas that have been subjected to various kinds of natural and manmade disturbance.

Distribution in the United States: Watermilfoil occurs in thirty-three states east of the Mississippi River and has recently been found in Colorado. It is abundant in the Chesapeake Bay, the tidal Potomac River, and several Tennessee Valley reservoirs.

Habitat in the United States: Typical habitat for Eurasian watermilfoil includes fresh to brackish water of fish ponds, lakes, slow-moving streams, reservoirs, estuaries, and canals.. It is tolerant of many water pollutants. 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. By altering waterways, humans have created a new and unnatural niche where milfoil thrives.

Background: Eurasian watermilfoil was accidentally introduced from Eurasia in the 1940s. Two theories exist as to how it entered North America: (1) it escaped from an aquarium, or (2) it was brought in attached to commercial or private boats. A resort owner is thought to have introduced watermilfoil into the Tennessee Valley Authority reservoir system in 1953.

Methods of Reproduction and Dispersal: Most regeneration of Eurasian watermilfoil is from rhizomes, fragmented stems, and axillary buds that develop throughout the year. Flower spikes often remain above water until pollination is complete, then resubmerge. Although seeds are usually viable, they are not an important means of dispersal.

Current Management Approaches: Large harvesting equipment can be used to mechanically remove milfoil in larger areas; a sturdy hand-rake can be used for smaller areas. Other available options include manipulation of water level, light penetration and chemical control. Potential impacts to existing native aquatic plant species should be evaluated carefully before implementing any of these techniques. For the single harvest, removal should take place just before peak biomass is obtained (early summer). Substantial regrowth may occur if this is done too early. Better results appear with multiple harvests in the same growing season. If multiple harvests are not possible, then sustaining annual harvests is an option. All fragments of milfoil plants must be removed to achieve adequate control.

Where water levels are under manual control, raising or lowering of the water can be an effective way to reduce the growth of milfoil. By raising the water level, plants can be "drowned" by not having access to enough light. By lowering the water level, plants can be dehydrated and, at the right time of the year, frozen to death. This type of control is best used in conjunction with herbicides and shade barriers.

Bankside plantings, floating native plant species, light limiting dyes, or shade barriers are effective ways of reducing the amount of light reaching the plants and may reduce overall growth rates. Barriers can be used to prevent the movement and spread of aquatic weeds in ponds and lakes. A barrier is usually a suspended blocking screen that hangs vertically from a cable to a depth of about 4 meters; the cable is suspended by drum floats.

Fluridone (the active ingredient in Sonar AS) is a selective herbicide for milfoil and several other exotic aquatic weeds. There are no restrictions on swimming, fishing, or drinking after application, and season-long control can be achieved with one application. Fluridone is available in liquid or granular form and can be used as a spot treatment or on an entire waterway. For best results, applications should be made before or during the early stages of active growth.

Description: Originally form Europe, garlic mustard is a cool season biennial herb in the mustard family (Brassicaceae). The leaves are stalked, alternate, triangular to heart-shaped, coarsely toothed, and give off an odor of garlic when crushed. First-year plants appear as a rosette of scallop edged, kidney-shaped leaves close to the ground. Rosettes remain green through the winter and develop into mature flowering plants the following spring. Flowering plants of garlic mustard reach from 2 to 3-1/2 feet in height and produce buttonlike clusters of small white flowers, each with four petals in the shape of a cross. Fruits are slender capsules 1 to 2.5 inches long that produce a single row of oblong black seeds with ridged seed coats. The seeds are viable for up to 6 years, with a single plant producing over 500 seeds.

Habitat and Distribution: Garlic mustard grows in rich moist upland forests and on wooded streambanks. It is shade tolerant and readily invades disturbed areas such as roadsides and trail edges. Garlic mustard cannot tolerate acidic soils, including undrained peat or muck. Distribution covers much of the eastern and midwestern U.S.

Methods of Reproduction and Dispersal: Reproduction is primarily by seed. Seeds are dispersed in late summer but do not germinate until the second spring due to their long dormancy period (20 months).

Description: Originally from Europe, glossy and common buckthorns are deciduous shrubs or small trees with thorny branches. Plants can grow to 20-25 feet high, and produce abundant black fruit that are eaten and dispersed by birds. Their bark is gray to brown with prominent, often elongate, lighter-colored lenticels. Cutting a branch of either species exposes a yellow sapwood and a pinkish to orange heartwood.

Common buckthorn: Leaves are green, smooth, oblong, slightly toothed, and opposite in arrangement. Flowers from May through June and fruit ripens August through September.

Glossy buckthorn: Leaves are green, glossy, elliptical, round-toothed, hairy on the underside, and alternate in arrangement. Flowers from late May until the first frost and produces fruit from early July through September.

Methods of Reproduction and Dispersal: Both buckthorns are characterized by long distance dispersal ability, prolific reproduction by seed, and wide habitat tolerance. Under full sun conditions, they can begin to produce seed a few years after establishment. Fruit production may be delayed for 10 to 20 years in shaded habitats. The abundant fruits are eaten birds, thus encouraging long-distance dispersal. Seedlings establish best in high light conditions, but can also germinate and grow in the shade. The exotic buckthorns have very rapid growth rates and resprout vigorously after they have been cut. Typical of several non-native understory shrub species, buckthorns leaf out very early and retain their leaves late in the growing season, thereby shading out native wildflowers.

Habitat and Distribution: Both species are tolerant to stress and drought, and can grow with very little soil. They have become naturalized in the northern U.S.. Common buckthorn is a problem species mainly in the understory of southern oak, oak-beech, maple, and riparian woods, prairies, and savannas. It aggressively competes with local flora, mainly on well-drained soils. Glossy buckthorn is an aggressive invader of wet soils. It has become a problem in wetlands as varied as acidic bogs, calcareous fens, and sedge meadows. It is capable of growing both in full sun and in heavily shaded habitats. The species is not confined to wetlands, however, and grows well in a wide variety of upland habitats, including old fields and roadsides. Neither species is adversely affected by nutrient-poor soils.

Ecological Threat: Invasive, especially in calcareous soils where they replace woodland wildflowers and can change the structure of the plant community. They thrive in disturbed habitats, and establish in suitable natural areas. Plants invade selectively cut or grazed woods, and impede natural succession by forming dense monotypic thickets. Although their aggressively invasive growth patterns have created problems in many areas, exotic buckthorns are still legally sold and planted as ornamentals.

Description: Native of Japan this dense, thorny shrub grows 2 to 3 feet tall with abundant red berries. Leaves are semi-evergreen, grow in alternate clusters, and range in color from from burgandy to bright green. Yellow flowers bloom in May, are about one third of an inch wide, and are solitary or in small clusters of 2-4 blossoms. The bright-red fruits mature in mid-summer and hang from the bush during autumn and into winter. The berries are small, oblong, and found singly or in clusters. Several cultivars of this species are sold as ornamentals.

Methods of Reproduction and Dispersal: The plant reproduces from prolific seeds, rhizomes, and layering. Seeds have a germination rate as high as 90%. Birds and rabbits are known to eat the seeds and distribute the species. Branches root freely when they touch the ground; thus allowing single plants to become quite large. Japanese barberry competes poorly with grasses and may succumb to drought conditions.

Habitat and Distribution: Japanese barberry prefers well-drained soils, although it has been found in wet, calcareous situations, (specifically in a black ash swamp). It grows mainly in woodlands under closed canopy. It is shade tolerant, and extensive populations can establish in a short time under forest cover.

Ecological Threat: This plant is often sold as an ornamental but can escape cultivation and become a problem in wooded areas because its dense cover shades out native understory herbs. In areas with alkaline soil, it can become a dominant in open pastures. Cows and deer only browse early spring growth, and established plants have no natural predators to keep it under control.

References

Invasive Species Council and Advisory Committee

Wisconsin Department of Natural Resources

Description: Originally from Asia the knotweeds are herbaceous perennials with upright jointed stems and alternate thick leaves. Stems are hollow, bamboo-like, and remain upright through the winter giving a woody appearance.

Japanese knotweed: Height of 3-6 feet tall. Leaves are oval to rounded with a flat base. Small greenish-white flowers occur in clusters out of leaf axils in late August to September. Flowers increase in size with maturity.

Giant knotweed: Similar appearance to Japanese knotweed, but taller (up to 12 feet or taller) and larger leaves (up to 1 foot long). Leaves have a heart-shaped base rather than flat. Flowers are smaller than Japanese knotweed and do not increase in size with maturity.

Methods of Reproduction and Dispersal: Reproduction can be by seed but is primarily by rhizomes, which may reach a length of 40 to 60 feet. These buried rhizomes are very tough and have been known to grow through 2 inches of asphalt. Small fragments of rhizome can be dispersed long distances by water or animals.

Habitat and Distribution: Giant knotweed shares habitat with Japanese knotweed. Both species are found along stream banks, in moist waste places, neglected gardens, roadsides, and railroad rights-of-way. Japanese knotweed has become naturalized in North America, where it is found from Newfoundland and many parts of the northeastern U.S., and west to California and the Pacific Northwest. Giant knotweed is also found throughout the U.S.

Ecological Threat: Japanese and giant knotweed are very aggressive plants that are capable of crowding out all other vegetation, degrading native plant and animal habitat. They are difficult to control because of their extremely vigorous rhizomes that form a deep, dense mat. In addition, plants can resprout from fragments; along streams, plant parts may fall into the water to create new infestations downstream.

Note: This plant is considered a noxious weed by the state of Wisconsin. Landowners are required to take control measures against its spread.

Native Range: Europe and Asia 

Description: Leafy spurge is characterized by plants containing a white milky sap and flower parts in threes. Leafy spurge is an erect, branching, perennial herb 2 to 3½ feet tall, with smooth stems and showy yellow flower bracts. Stems frequently occur in clusters from a vertical root that can extend many feet underground. The leaves are small, oval to lance-shaped, somewhat frosted and slightly wavy along the margin. The flowers of leafy spurge are very small and are borne in greenish-yellow structures surrounded by yellow bracts. Clusters of these showy, yellow bracts open in late May or early June, while the actual flowers do not develop until mid-June.

Ecological Threat: Leafy spurge displaces native vegetation in prairie habitats and fields through shading and by usurping available water and nutrients and through plant toxins that prevent the growth of other plants underneath it. Leafy spurge is an aggressive invader and, once present, can completely overtake large areas of open land.

Distribution in the United States: Leafy spurge occurs across much of the northern U.S., with the most extensive infestations reported for Montana, North Dakota, Nebraska, South Dakota, and Wyoming. It has been identified as a serious pest on a number of national parks and on preserves of The Nature Conservancy in eleven northern states.

Habitat in the United States: Leafy spurge tolerates moist to dry soil conditions but is most aggressive under dry conditions where competition from native plants is reduced. It is capable of invading disturbed sites, including prairies, savannas, pastures, abandoned fields and roadside areas.

Background: Leafy spurge was transported to the U.S. possibly as a seed impurity in the early 1800s. First recorded from Massachusetts in 1827, leafy spurge spread quickly and reached North Dakota within about 80 years.

Biology and Spread: Leafy spurge reproduces readily by seeds that have a high germination rate and may remain viable in the soil for at least seven years, enhancing its chances of recovery over time. Its seed capsules open explosively, dispersing seed up to 15 feet from the parent plant and may be carried further by water and wildlife. Leafy spurge also spreads vegetatively at a rate of several feet per year. The root system is complex, can reach 15 or more feet into the ground, and may have numerous buds.

Management Options: Because of its persistent nature and ability to regenerate from small pieces of root, leafy spurge is extremely difficult to eradicate. Biological control offers a highly promising management tactic for leafy spurge. The U.S. Department of Agriculture has shown success using six natural enemies of leafy spurge imported from Europe. These include a stem and root-boring beetle (Oberea erythrocephala), four root-mining flea beetles (Aphthona spp.) and a shoot-tip gall midge (Spurgia esulae). Large scale field-rearing and release programs are carried out cooperatively by federal and State officials in many northern states. The results are not as immediate as when herbicides are used but, if pesticide use is kept to a minimum, large numbers of these agents build up within a few years and have shown impressive results. Several systemic herbicides have been found to be effective if applied in June, when the flowers and seeds are developing, or in early to mid-September, when the plants are moving nutrients downward into the roots. Preliminary research suggests that chemical treatment in the fall followed by a spring burn to reduce seed germination may be an effective strategy for reducing leafy spurge infestations. Multiple treatments are necessary every year for several years, making leafy spurge control an extremely expensive undertaking. If left uncontrolled for a single year, leafy spurge can reinfest rapidly. Prescribed burning, in conjunction with herbicides, may also be effective.

Description: Originally from China and Japan, oriental bittersweet is a deciduous woody vine with alternate leaves that are glossy green, round, and toothed. The vine has a twining or trailing growth pattern, with constricting and girdling stems that can reach 4 inches in diameter. Flowers are greenish-yellow in color, and are produced in the leaf axils. In autumn thick yellow capsules open to display a bright red fleshy fruit that persists through most of the winter. It is often confused with American bittersweet which has flowers at stem tips and leaves that are longer and more pointed.

Methods of Reproduction and Dispersal: An extremely invasive plant that reproduces by seeds, above ground stems (stolons), below ground stems (rhizomes) and shoots from the roots (root-suckering). Birds show a preference for the fruits over native bittersweet because they are brighter and more numerous. This leads to increased dispersal of Oriental bittersweet over American bittersweet (Celastrus scandens).

Habitat and Distribution: In the northeastern U.S., exotic Oriental bittersweet appears to be displacing the native American bittersweet, which occurs in similar habitats, through competition and hybridization. It prefers open sites such as road sides, hedgerows, and thickets but also persists in shaded forested areas. Distribution is throughout most of the northeast, south to Georgia and west to Iowa.

Ecological Threat: Dense stands of vines can shade and suppress native vegetation. Its climbing habit kills nearby plants by preventing photosynthesis, constricting stems, and uprooting plants. Once established, it is very difficult to control.

Description: Originally from Europe, purple loosestrife is an erect perennial herb in the loosestrife family, with a square, woody stem and opposite or whorled leaves. Leaves are lance-shaped, stalkless, smooth margined, and heart-shaped or rounded at the base. Plants are usually covered by dense velvety hairs. Loosestrife plants grow from four to ten feet high, depending upon conditions, and produce a showy display of magenta-colored flower spikes throughout much of the summer. Flowers have five to seven petals. Mature plants can have from 30 to 50 stems arising from a single rootstock.

Habitat and Distribution: Purple loosestrife is capable of invading many wetland types, including freshwater wet meadows, tidal and non-tidal marshes, river and stream banks, pond edges, reservoirs, and ditches. According to the U.S. Fish and Wildlife Service, purple loosestrife now occurs in every state except Florida.

Methods of Reproduction and Dispersal: Purple loosestrife has an extended flowering season, generally from June to September, which allows it to produce large quantities of seed. The flowers require pollination by insects, for which it supplies an abundant source of nectar. A mature plant may have as many as thirty flowering stems capable of producing an estimated two to three million, minute seeds per year. Seeds remain viable in the seed bank for a number of years and can germinate over a wide range of environmental conditions. Purple loosestrife also readily reproduces vegetatively through underground stems at a rate of about one foot per year. Many new stems may emerge vegetatively from a single rootstock of the previous year.

Ecological Threat: 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. Plants are very resilient to management and can withstand cutting, crushing, and burning.

Description: This perennial grass is a native species but aggressively invasive possibly due to selective cultivation for vigorous growth. This large, coarse grass has erect, hairless stems, usually from 2 to 6 feet tall. The gradually tapering leaf blades are 3 1/2-10 inches long, 1/4-3/4 inch wide, flat, and often harsh on both surfaces. The compact flowers are erect or sometimes slightly spreading and range from 3-16 inches. Single flowers occur in dense clusters in May to mid-June or August and are green or slightly purple at first, then become tan. The species growth form is highly variable. It is extremely difficult, if not impossible, to distinguish the native and non-native ecotypes. Reed canary grass closely resembles orchard grass (Dactylis glomerata). It differs from orchard grass in that reed canary grass's leaves are much wider, the inflorescence is more narrow and pointed, and the individual flowers have a different shape. Reed canary grass should be accurately identified before attempting any control measures.

Habitat and Distribution: Common along waterways and in meadows, wet prairies, stream banks, lower valleys, rivers and pond banks, and along drainage ditches. Distributed throughout most of the U.S. except southern states.

Ecological Threat: A very aggressive species that is highly competitive with other plants. It begins growth in early spring, grows vertically for 5-7 weeks, and then begins to spread laterally. It poses a major threat to many wetland areas because of its persistence and rapid growth. It may inhibit growth of other species for 3-5 months, eventually eliminating these species and creating monocultures. It is of particular concern because of the difficulty of selective control.

Native Range: Central Europe, east to central Russia, Caucasia, and western Siberia.

Description: Spotted knapweed is a biennial or short-lived perennial member of the Sunflower (Asteraceae) family. Its name is derived from the spots formed by black margins on the flower bract tips. Spotted knapweed typically forms a basal rosette of leaves in its first year and flowers in subsequent years. Rosette leaves are approximately 8 inches long by 2 inches wide, borne on short stalks, and deeply lobed once or twice on both sides of the center vein, with lobes oblong and wider toward the tip. The taproot is stout and deep. Flowering stems are erect, 8 to 50 inches tall, branched above the middle, and sparsely to densely hairy. Stem leaves alternate along the stem, are unstalked, and may be slightly lobed, or linear and unlobed. Leaf size decreases towards the tip of the stem.

Flowers are purple to pink, rarely white, with 25 to 35 flowers per head. Plants bloom from June to October, and flower heads usually remain on the plant. Flower heads are oblong or oval shaped, ¼ inch wide and ½ inch across, and are single or borne in clusters of two or three at the branch ends. Leaf like bracts surrounding the base of the flower head are oval and yellow green, becoming brown near the base. The margins of these bracts have a soft spine like fringe, with the center spine being shorter than the lateral spines. The brown, oval seeds are 1/16 to 1/8 inch long, with pale longitudinal lines and a short fringe on one end.

Ecological Threat: Spotted knapweed infests a variety of natural and semi-natural habitats including barrens, fields, forests, prairies, meadows, pastures, and rangelands. It outcompetes native plant species, reduces native plant and animal biodiversity, and decreases forage production for livestock and wildlife. Spotted knapweed may degrade soil and water resources by increasing erosion, surface runoff, and stream sedimentation. It has increased at an estimated rate of 27% per year since 1920 and has the potential to invade about half of all the rangeland (35 million acres) in Montana alone.

Distribution in the United States: Spotted knapweed is a widely distributed species reported to occur throughout Canada and in every state in the U.S. except Alaska, Georgia, Mississippi, Oklahoma and Texas (see map). It has been designated as a noxious weed in Arizona, California, Colorado, Idaho, Minnesota, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oregon, South Dakota, Utah, Washington, and Wyoming.

It has been identified as invasive in natural areas by eighteen organizations in twenty-six states (Arizona, California, Colorado, Connecticut, Delaware, Kentucky, Idaho, Illinois, Massachusetts, Maryland, Michigan, Minnesota, Montana, North Carolina, New Jersey, New York, Oregon, Pennsylvania, South Dakota, Tennessee, Utah, Virginia, Washington, Wisconsin, West Virginia, and Wyoming). Fifteen national parks also identify spotted knapweed as an invasive plant and a threat to natural habitats.

Habitat in the United State: Spotted knapweed is found at elevations up to and over 10,000 feet and in precipitation zones receiving 8 to 80 inches of rain annually. Spotted knapweed prefers well-drained, light-textured soils that receive summer rainfall, including open forests dominated by ponderosa pine and Douglas fir, and prairie habitats dominated by Idaho fescue, bluebunch wheatgrass, and needle-and-thread grass. Disturbance allows for rapid establishment and spread; however, spotted knapweed is capable of invading well managed rangelands. Spotted knapweed does not compete well with vigorously growing grass in moist areas. In seasonally dry areas, spotted knapweed's taproot allows it to access water from deep in the soil, beyond the reach of more shallowly rooted species.

Background: Spotted knapweed was introduced to North America from Eurasia as a contaminant in alfalfa and possibly clover seed, and through discarded soil used as ship ballast. It was first recorded in Victoria, British Columbia in 1883 and spread further in domestic alfalfa seeds and hay before it was recognized as a serious problem.

Methods of Reproduction and Dispersal: Spotted knapweed plants in North America generally live 3 to 7 years but can live up to nine years or longer. Plants regrow from buds on the root crown. Reproduction is by seed, and plants are capable of producing 500- 4,000 seeds per square foot per year. About 90% of the seeds are viable at the time of dispersal, and they can remain viable in the soil for 5-8 years. Most seeds are dispersed near the parent plant but can be transported by people, wildlife, livestock, vehicles, and in soil, crop seed, and contaminated hay. Gravel pits, soil stockpiles, powerlines, grain elevators, railroad and equipment yards are important seed distribution points.

Current Management Approaches: The most cost effective management strategy for spotted knapweed is to prevent its spread to non-infested areas. Spread by seed can be minimized by avoiding travel through infested areas; by cleaning footwear, clothing, backpacks, and other items after hiking through infested areas; by not grazing livestock when ripe seeds are present in the flower heads; and by using weed free hay.

Manual and Mechanical. Small infestations of spotted knapweed can be controlled by persistent hand-pulling done prior to seed set. Gloves should be worn because of the possibility of skin irritation. Because spotted knapweed can regrow from the base, care must be taken to remove the entire crown and taproot.
Biological control. A variety of natural enemies are used as biological control agents for large infestations of spotted knapweed. Most biocontrol techniques use insect larvae to damage the root, stem, leaf, or flower. Two species of seed head flies, Urophora affinis and U. quadrifasciata, are well-established on spotted knapweed. The larvae of these species reduce seed production by as much as 50% by feeding on spotted knapweed seed heads and causing the plant to form galls. Three moth species (Agapeta zoegana, Pelochrista medullana, and Pterolonche inspersa) and a weevil (Cyphocleonus achates) that feed on spotted knapweed roots have also been released.
The collective stress on the plant caused by these insects reduces seed production and may lead to reduced competitiveness. Biological control agents may be more effective when combined with other control methods such as herbicides, grazing, and revegetation with desirable, competitive plants.

Chemical. Control of spotted knapweed infestations using three chemical herbicides (2,4-D, clopyralid, and picloram) has been reported but is problematic. Existing plants can be killed with 2,4-D but it needs to be reapplied yearly to control new plants germinating from seed stored in the soil. Picloram is a more persistent herbicide and has controlled knapweed for three to five years when applied at 0.25 lb/acre at any stage of plant growth; or with clopyralid (0.24 lb/acre) or clopyralid (0.2 lb/acre) plus 2,4-D (1 lb./acre) applied during bolt or bud growth stage. In the absence of desirable native grasses, longevity of control may be increased by revegetating with competitive grasses and forbs. Picloram may pose a risk of groundwater contamination where soils are permeable, particularly where the water table is shallow.

Other methods. Long-term grazing by sheep and goats has been found to control spotted knapweed. Burning, cultivation, and fertilization typically are not effective on spotted knapweed unless combined with other methods of control.

Description: Wild parsnip is a member of the Umbelliferae (parsnip) family. Rosettes grow close to the ground and bear leaves averaging six inches in height. The plant has a long, thick taproot, which is edible. Flowering plants produce a single, thick stem that contains hundreds of yellow umbellate flowers. The lateral flowers often overtop the terminal flowers. Depending on the habitat and growing conditions, individual flowering plants range to over four feet in height. Leaves are alternate, pinnately compound, branched, and have saw-toothed edges. Each leaf has 5-15 ovate to oblong leaflets with variable toothed edges and deep lobes.

Wild parsnip can be confused with prairie parsley (Polytaenia nuttallii), a native prairie species listed as threatened in Wisconsin. Its flowers and leaves resemble those of wild parsnip. Comparatively, flowers of the prairie parsley plant are light-yellow, sparse, and typically found at the end of the stem. The leaves are pinnately compound like those of the wild parsnip, but are oblong with few teeth.

Distribution and Habitat: Wild parsnip is tolerant of a wide range of conditions, including dry, mesic, and wet-mesic prairies; oak openings; and calcareous fens. It is shade-intolerant and prefers sunny conditions.

Life History and Effects of Invasion: Wild parsnip can cause phytophotodermatitis to the skin. If the plant juices come in contact with skin in the presence of sunlight, a rash and/or blistering can occur, as well as skin discoloration that may last several months.

This species reproduces readily from seed. Seeds are fairly large and many are produced on one plant. As a monocarpic perennial, wild parsnip spends one or more years as a basal rosette. When conditions are favorable, it flowers, produces seed, and dies. Look for the large, coarse, flower spikes and yellow flowers from the first of June to the middle of July (although some plants may continue flowering through late summer). Optimal growing conditions apparently stimulate an increase in flowering. Apparently seeds take at least three weeks from flowering to become viable.
Wild parsnip slowly invades an area in waves following initial infestation. Once the population builds, it spreads rapidly. This species is an aggressive, Eurasian weed that frequently invades and modifies a variety of open habitats.
 

Controlling Wild Parsnip

Caution: Care should be taken to avoid skin contact with the juices of this plant. Proper clothing (gloves and a long-sleeved shirt) must be worn to prevent the phytophotodermatitic effects.

Mechanical Control: The best way to control wild parsnip is early detection and eradication. A very effective control method is to cut the entire root just below ground level with a sharp shovel or spade. Cutting below ground level prevents resprouting. In some soil types in wet conditions, the plants can be pulled out of the ground by hand. All seeds must be removed from the site and disposed of in a landfill or by burning.

If the population is too large to hand-cut or pull, a power brush-cutter can be used just after peak flowering and before the seeds set. Plants may resprout when cut above the ground, and should be cut again a few weeks later to prevent flowering. Cutting done after seed set will greatly reduce the likelihood that the plants will be able to resprout and flower. Plants cut at this time must all be gathered and removed from the site to prevent mature seed from developing and falling to the ground. Another effective way to eliminate reseeding is to hand-collect all seeds after they have set. If control of flowering or seeding plants is carried out over several years, the population will decrease as the seed bank is depleted.

Burning does not seem to impact the plants themselves -- they quickly resprout. However, in the darkened soil following a burn, these rosettes are easy to recognize and can be controlled by hand-digging. Prescribed burning stimulates increased growth in prairie species that may potentially decrease parsnip populations through competition.

Chemical Control: Chemical controls are effective, but should be used sparingly on quality natural areas. The best method is to burn the site, then follow with spot application of 1-3% active ingredient glyphosate. Immediately after a burn, wild parsnip is one of the first plants to green. Glyphosate can be spot applied to the basal rosette of the parsnip with little effect on dormant species.

History:  As its name suggests, Siberian pea-shrub or 'caragana' is native to Siberia and Manchuria. Unlike many of our invasive plants, this one is invading north to south and is a big problem in Canada and the upper Midwest. It was promoted in the early 1900's and is still sold as an ornamental and for shelterbelt and wildlife plantings.

Description: Appearance: Upright shrub or small tree, up to 18' high. Narrow branching, gray bark and branches; young twigs, yellowish-green.

Leaves: Alternate, compound, 2- 4" long consisting of 8 -12 pairs of one-inch elliptic-shaped leaflets.

Flowers: Pea flowers are yellow, single, tubular, at the end of a stalk that grows from the leaf axil; blooms in May - June.

Fruit: Pods 1- 2" long, pencil-shaped, sharply pointed, brown and smooth.

Ecological Threat: It invades savanna and woodland edge environments where it competes with native shrubs. Birds and mammals spread it quite readily via seeds. Pea-shrub can invade disturbed grasslands as well. There are only two sites known for this shrub on the CNNF.

Control: Mechanical - Hand pulling can be an effective control method for small seedlings. Mowing or cutting in early and late June for several years can reduce stem heights and infestations. Prescribed burning can be variable. After repeated prescribed burns, the stump of the tree may re-sprout but will eventually become weakened.

Chemical - Glyphosate and triclopyr can be effective in controlling Caragana. Cut-stump methods can be effective if the trunk is cut as close to the ground as possible and herbicides are immediately applied to the cut surface of the tree. A basal bark spray treatment may also be successful. Contact your local county extension agent for recommended use rates, locations, and timing.

Biological - No biological control agents are available for Caragana control, but the tree is susceptible to stem decay, branch cankers, and Septoria leaf spot. Blister beetles are also commonly found on the tree in mid- to late-summer.

References:

USDA, NRCS. 2008. The PLANTS Database (8 October 2008). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

Minnesota Department of Natural Resources. 2008. The Minnesota Department of Natural Resources Website (online). Accessed 2008-10-8.

Purpose

Who can you turn to for help with invasive species? The Invasive Species Cooperatives of Northern Wisconsin.

Invasive species cooperatives are local organizations that integrate all invasive plant management resources across jurisdictional boundaries in order to benefit entire communities. Many are started by local citizens, city, county, state, tribal, and federal leaders to more effectively control invasive species across property ownership boundaries. As in any cooperative, the group gains by sharing the often limited resources available (funds, equipment, time, labor) to control weed populations across several ownerships. This concept started in the western states as "Cooperative Weed Management Areas" or CWMAs.

Why the big deal about invasive species? Besides threatening our natural ecosystems, these non-native invasive species cost us money in higher prices and can be generally problematic and even dangerous. Think about the farmer who has to spend time and money on weeds; you pay more for food. Think about your favorite hunting or hiking area overgrown with buckthorn; you can't walk through it. Think about your yard infested with wild parsnip; you can get blistering burns when you brush up against it.

Partners

The Chequamegon-Nicolet National Forest is now a major partner in four cooperatives, assisting with the effort to control invasive species throughout northern Wisconsin. The four cooperatives deal with weed issues in the following counties:

• Northwoods CWMA (Ashland, Bayfield, Douglas, Iron) Contact Matt Bushman, district botanist 715-373-2665
• Upper Chippewa Invasive Species Cooperative (Sawyer, Price, Rusk, Taylor) Contact Ann Hoefferle, zone botanist 715-748-4875
• Vilas/Oneida CWMA (Vilas and Oneida) Contact Marjy Brzeskiewicz 715-762-2461 or Ted Ritter 715-479-3738
• Wisconsin DNR

How You Can Help

By joining your local CWMA you can provide assistance to your neighbors as well as get help in dealing with invasive species issues in your own backyard. By joining together, we can accomplish much more than any of us can individually. Let's all "pull together"!