Invasive Species Management

Spraying exotic species.

Refuge personnel identify and manage exotic and invasive species using a variety of techniques. 

 Invasive Plant Inventory


Glossy Buckthorn | Spotted Knapweed | Tartarian Honeysuckle | Reed Canary Grass
Purple Loosestrife | Leafy Spurge | Multiflora Rose

September 1999
Sally Petrella M.S., Nicole Shutt B.S., and Dick McNeill Ph.D.

Invasive non-native plants species are an increasing threat to native populations of plants and animals. Exotic plant species introduced into favorable habitats can reproduce in large numbers; their populations often literally explode. This is primarily due to the fact that many non-native species are more aggressive and adaptable because they have no natural predators and readily replace the native plants. Recently, a large increase in certain species of exotic plants has been noted in Seney National Wildlife Refuge (SNWR).

The Seney National Wildlife Refuge consists of more than 95,000 acres and was established in 1935 for the production and protection of migratory birds and other wildlife. The refuge is composed of a rich mosaic of marsh, swamp, bog, grassland and forest, with nearly two-thirds wetlands.

In August 1999, SNWR's manager Mike Tansy discussed the problem of invasive species in the refuge with Sally Petrella, Nicole Shutt, and Dick McNeill and asked them to conduct a preliminary survey of the 4-6 exotic plant species that are thought to pose the biggest threat to the refuge.

Sally Petrella, M.S., is a recent graduate in biology at the University of Michigan, and a biological intern at SNWR. Nicole Shutt, B.S., is a recent graduate from the University of Michigan's School of Natural Resources and Environment, and also interns at SNWR. Dick McNeill, Ph.D., is a retired professor of ecology and curator of SNWR's herbarium.

We surveyed alongside all driveable refuge roads (approximately 85 miles) and the Pine Ridge Nature Trail (1.5 miles) to record the prevalence of seven target species: glossy buckthorn (Rhamnus frangula), purple loosestrife (Lythrum salicara), spotted knapweed (Centaurea maculosa), leafy spurge (Euphorbia esula), tartarian honeysuckle (Lonicera tatarica), reed canary grass (Phalaris arundinacea) and multiflora rose (Rosa multiflora). Nearly all of the refuge roads are two track with a vegetational strip down the middle. Although 35 invasive exotic plants have been documented in Seney National Wildlife Refuge (table 1), we limited the survey to the species that seem to pose the biggest threats due to their aggressiveness and suitability to SNWR. Six of our target species are considered Category One by Region 9 of the United States Forest Service: they are highly invasive, invading natural habitats and replacing native species. The last species, multiflora rose, is Category Two: moderately invasive, it may replace natives but only locally (USFS 1998).

Surveys were done by slowly driving each road and identifying the locations of the target species. Only 1-5% of the refuge's eastern portion where roads are present was surveyed. Additionally, Creighton Road, along the western border was surveyed. The western half of the refuge is wilderness area with no roads, therefore the interior was not surveyed. Locations were marked on a series of maps made using ArcView version 3.0a. All surveys were completed between August 16 through August 26, 1999. Prior to the survey, Dick McNeill traveled through the refuge and flagged many of the target species. He also brought in specimens to ensure accurate identification of all target species.

All of the target species except leafy spurge were very visible at the time of the survey because they were either flowering or fruiting. Leafy spurge was difficult to see because the flowers had dried and the vegetation surrounding it had grown taller. We were only able to find this plant based on reports from Dick McNeill and Mike Tansy, who had identified the plant earlier in the season. Therefore, leafy spurge and the other surveyed invasive species could be far more widespread than our data show.

Due to time constraints, we were unable to survey the refuge beyond areas alongside and adjacent to the roads. Obviously, this method is very biased. We recommend a more thorough survey be done in the future.

Results and Recommendations for each of the target species:

Glossy buckthorn (Rhamnus frangula)

Glossy buckthorn (also known as smooth buckthorn) is a small tree or tall shrub, growing to 6 meters high and supporting an open crown of low branches. Leaves are alternate, simple, entire and oval. The blades are 3-7 cm long, glossy dark green above, lighter beneath, and have 8-9 pairs of veins. Flowers are perfect, pale yellow five-petaled and inconspicuous, borne in axillary clusters May through June. Plants are polygamous or dioecious. The fruit is a yellow-green drupe that gradually turns red to black as it ripens July through September. The drupe encloses 2-3 nutlike pits that contain the seeds (Barnes and Wagner 1981).

Native to Eurasia, glossy buckthorn can invade wetlands and out compete native vegetation outside of its native habitat. Introduced as an ornamental shrub and first collected in Michigan in 1934, glossy buckthorn tolerates some shade and grows quickly in almost any moist habitat. Consuming a lot of water, an acre of buckthorn can reduce the water table as much as a foot and a half (Devine 1999). It forms dense clones and resprouts vigorously when cut. The plant leafs out earlier and retains its leaves longer than other shrubs. This characteristic may aid in its identification.

Buckthorn is often noted as a forage food for birds and other wildlife but its berries and branches may be offering false promises for birds. It is reported that the fruit has a laxative effect on birds (Voss 1985), passing through the digestive tract within 10 minutes (McGowan-Stinski, personal communication). The pattern of young buckthorn seedlings in close proximity to 2-3 year old fruiting trees supports this finding, but it is doubtful that the birds receive much nutrition from buckthorn. Buckthorn may also offer birds less in the way of a nesting structure. In a recent study, robins nesting in buckthorn and honeysuckle were more likely to have their nests predated due to lower nest heights caused by the absence of thorns, sturdy branches, and reduced basal cover in these exotic species ( Schmidt and Whelan in press).

Glossy buckthorn is densely concentrated within a 1-2 mile radius surrounding the refuge headquarters and Visitor Center. Additionally, scattered patches are found on B-1, D-1, and G-1 Pools along Marshland Wildlife Drive and along C-2 Pool. The densest stands of buckthorn are found along the dike west of the Show Pools and it has spread east past the refuge boundary in this area. Some stands are so dense that only buckthorn is growing there.

The plant is mainly found along roads and dikes but extends into the wetlands as far as 3 meters from the road on the eastern edge of J-1 Pool and along the entrance road. Some islands in the Show Pools and along the northern portion of the Pine Ridge Nature Trail have also been colonized. Young plants are growing in forests near the trail. On September 2, 1999, Jack McGowan-Stinski from the Michigan Nature Conservancy toured some of the most infested areas of the refuge and gave a hands on demonstration of the methods the Nature Conservancy uses to remove buckthorn and other invasives. Jack has been experimenting with various methods of removing glossy buckthorn from a fen in Michigan's lower peninsula for the past five years.

Glossy Buckthorn Locations and Density, 1999.
Glossy Buckthorn Locations and Density, 1999.

We recommend a massive removal of all buckthorn from the refuge and from all adjacent non-refuge property, beginning at the perimeter areas and moving inward to the most infested areas. Treating the perimeter areas first will reduce the chance of invasion farther into the refuge.

Jack McGowan-Stinski of the Michigan Nature Conservancy has been successful in removing glossy buckthorn using the following methods. Seedlings with a stem diameter of less than 1 cm in diameter can be removed by hand pulling or burning with a propane torch. Larger plants should be cut 6 inches above the ground and then treated with herbicide immediately (within 5 minutes) following the cutting, applied by sponge applicator. Rodeo or Accord, wetland-approved herbicides, should be used in wet areas, mixed with water to a 13-14% active ingredient in the final mix. All treated areas should be flagged and repeatedly checked and retreated for up to 5 years.


Spotted Knapweed (Centaurea maculosa)

Spotted knapweed is an herbaceous biennial plant that is intolerant to shade and has a stout taproot and purple to pink flowers. The up to 2 cm thick stems are branched and grow up to 1 meter high. The basal leaves are entire to pinnately parted and grow to 15 cm. The stem leaves are pinnately divided. The flowers are pinkish-purple rays that grow singly at the ends of branches. The involucral bracts are stiff and tipped with dark fringe (Westbrook 1998).

Brought from Eurasia as a contaminant in alfalfa and clover seeds, spotted knapweed has several characteristics that allow it to outcompete native plants. A deep taproot enables it to survive very dry conditions. It thrives along roadsides and other open disturbed areas (USDA 1994). Quick early spring growth helps it to outcompete the native plants for light and nutrients. Spotted knapweed is also extremely prolific. Each flower produces 12-35 seeds. The seeds can stay dormant in the soil for 8-10 years. Botanists even suspect that the plant secretes a chemical that inhibits growth of surrounding vegetation (USDA 1994).

Spotted knapweed is found to some extent along virtually every road, dike and trail in the refuge. Large patches of it are also found in East Walsh Farm and Diversion Farm. The plant seldom extends very far from the edge of the roads, trails or dikes. Because of more competitive native plants, shade trees and bracken fern seem to effectively limit its spread beyond the roads.

Spotted knapweed first entered the refuge sometime in the 1980s but was not documented in the refuge until the 1995 Seney Annual Narrative Report. It was probably brought in with contaminated gravel used on refuge roads. Even today, gravel piles at the entrance to C-3 Pool and the entrance to Subheadquarters contain many spotted knapweed plants.

Because spotted knapweed is only found along roads, trails, dikes, and two hayfields, we recommend controlling it by mowing in the early spring before it flowers. Repeated mowing prior to flowering should reduce the seed production but will have to become a long term regimen due to the longevity of the seeds. In addition, all gravel piles must be sterilized or treated with herbicides prior to spreading on the refuge if spotted knapweed is to be controlled.


Tartarian Honeysuckle (Lonicera tatarica)
Tartarian honeysuckle is a deciduous upright shrub that grows 2-5 m. tall and is intolerant to shade. The leaves are egg-shaped, 2-3 cm long, opposite and short-stalked. The creamy white to pink or crimson flowers are paired, tubular, and less than 3 cm long. They are borne along the stem or in the leaf axis in early to late spring. The fruits are red or orange and have many seeds (NPCI 1999).

Brought from Eurasia to be planted as ornamental shrubs, exotic honeysuckles can rapidly form a dense shrub layer, crowding and shading out native plants. They release toxic chemicals that prevent other plant growth. Alien honeysuckles also compete with native plants for pollinators, possibly reducing the seed set for native species (NPCI 1999).

Tartarian honeysuckle surrounds the refuge headquarters and Visitor Center roads. A few isolated plants are found on the eastern section of Marshland Wildlife Drive.

Tartarian Honeysuckle Locations, 1999.
Tartarian Honeysuckle Locations, 1999.

We recommend manual removal of all tartarian honeysuckle and treatment of stumps with herbicide. Plants should be cut 6 inches above the ground and then treated with herbicide immediately (within 5 minutes) following the cutting, applied by sponge applicator. Rodeo or Accord, wetland-approved herbicides, should be used in wet areas, mixed with water to a 13-14% active ingredient in the final mix. All treated areas should be flagged and repeatedly checked and retreated for up to 5 years.


Leafy Spurge (Euphorbia esula)
Leafy spurge is an erect, branching perennial herb that grows to a meter tall and is intolerant to shade. It has smooth stems that contain a milky latex sap and showy yellow flower bracts. The leaves are small oval to lance-shaped and somewhat frosted along the margin. The first pair of leaves are opposite, later leaves are alternate (USFWS 1997). The flowers are small and borne in greenish-yellow structures surrounded by yellow bracts. While the yellow bracts open May through June, the actual flowers do not develop until mid-June. Leafy spurge has vertical and horizontal roots that can extend many feet underground and can form stems.

Brought in as a seed impurity from Europe in the 1800s, leafy spurge has become a serious pest in western U.S. rangelands where it invades grassland habitat, forming beautiful fields of inedible vegetation. In the same family as poinsettia, the stems and leaves contain a latex that is toxic to most grazing mammals. Thousands of acres of rangeland have been lost to leafy spurge; it reduces the productivity of grazing land by 50-75% (NPCI 1999).

Leafy spurge tolerates moist to dry conditions but is especially aggressive under dry conditions and in disturbed areas. The vertical root can reach 5 meters or more into the ground and the horizontal roots can spread almost a meter per year. The roots secrete allelopathic chemicals to reduce competition from other plants. One of the first plants to emerge in spring, vegetative stems are produced from existing roots in late April. The seeds have a high germination rate and are viable in the soil for up to 7 years. The seed capsules are explosive, dispersing seeds up to 5 meters and are also carried by water and wildlife (NPCI 1999).

Leafy spurge was found in two patches in two isolated locations within the refuge. One patch is approximately 15 by 5 meters and is located on Marsh Creek Road, south of T-2 West and north of Marsh Creek Pool. This patch is marked by a stake and flagging. The other patch of approximately 2 dozen plants is located near the J-I spillway, southeast of the bridge. Because the plant was not flowering and the native goldenrod was much taller than the spurge at the time of our survey, we easily could have overlooked other patches of leafy spurge.

Leafy Spurge Locations, 1999.
Leafy Spurge Locations, 1999.

We recommend immediate manual removal of plants and entire root system and treatment with herbicides. Leafy spurge is easier to control within the first two years of establishment, before the root system is well-established (USFWS 1997). Follow-up will be necessary to check for resprouts and seedlings. We also recommend a new survey be done in mid-June, when the plant is flowering above other plants.


Purple Loosestrife (Lythrum salicara)
Purple loosestrife is an erect herbaceous perennial of Eurasian origin. It grows up to 2 meters high, has a four-angled stem, and opposite, entire lance-shaped leaves 3-10 cm long. Brilliant purple flower spikes make this plant very obvious from mid-July to the end of September. The flowers have 5-6 petals and grow in the axils of bracts or leaves or are terminal (USFWS 1997).

Imported from Europe as a garden ornamental in the 1800s, purple loosestrife has overtaken many wetlands in Canada and the United States, crowding out native species and eliminating open water habitat. Rapid growth and an enormous reproductive capacity allow it to spread quickly. Each mature plant produces 30 or more flowering stems and can produce over 2.5 million seeds per year. It can propagate vegetatively from root and stem segments (USFWS 1997).

Purple loosestrife is encroaching from south of the refuge and was discovered in the refuge for the first time this season. The plant in the refuge was found along Marshland Wildlife Drive, at the edge of C-1 Pool.

Outside of the refuge, purple loosestrife is spreading, especially from the south. Two miles south of the refuge border, two plants were found along High Water Truck Trail near Duck Creek. Three miles south of the refuge boundary, plants were found alongside M-77, on the west side of the road. Approximately 6.5 miles south of the southern boundary numerous plants were found alongside Manistique River Road, beginning about 4 miles southwest of the Mead Creek Campground, and increasing in abundance further south. North of the refuge, one plant has routinely been found on the west side of M-77, 1.5 miles north of the refuge boundary.

Purple loosestrife was first documented 30 miles south of the refuge in 1989 (Annual Narrative 1989) and then found bordering the refuge in 1991 (Annual Narrative 1991). Treatment with herbicide followed by hand removal has slowed down the spread into the refuge.

Purple Loosestrife Locaitons, 1999.
Purple Loosestrife Locaitons, 1999.

We recommend constant vigilance and immediate removal of any purple loosestrife found within or near the refuge. Extremely difficult to control once established, early detection and prevention of loosestrife spread are the most effective defenses (USFWS 1997). This will require cooperation from private and public landowners. Plants should be removed before they go to seed and the entire plant including all roots and root tips must be removed. Plant locations should be flagged and rechecked every year.

Reed Canary Grass (Phalaris arundinacea)
Reed canary grass is a tall coarse perennial cool-season grass that grows 0.6-1.8 meters high. The stems are erect and hairless. The leaf blades are flat and tapering, 8-25 cm long, 0.6-2 cm wide, and often harsh on both surfaces. The single flowers bloom in dense clusters form May to August. Initially flowers are green and purple and turn tan as they ripen (Hutchinson 1999). The seeds are shiny brown with short hairs (Wisconsin Cranberry Growers 1999).

Reed canary grass is native to North America, but a Eurasian ecotype has been widely introduced. The Eurasian ecotype may be more aggressive but it is almost impossible to distinguish it from the native grass. Due its aggressive nature, hardiness, and rapid growth, reed canary grass can replace native wetland and wet prairie species. It grows best in wet soils and spreads by seed or rhizome. Rapid growth occurs in early spring, seeds ripen and shatter in late June, and growth declines by mid-August (Hutchinson 1999).

Reed canary grass is found to date in one approximately 30-acre patch in the eastern part of the refuge, between pools J-1 and G-1. Noted as a problem in the refuge's Weed Inventory Surveys since 1997, this 30 acre patch is in a former wet meadow, contains few other plant species, and may be expanding into the surrounding wetlands. The grass may be growing in other locations in SNWR but it only appears to be crowding out natives and expanding in this one location. It has been found in the refuge as far back as 1940 when a specimen was collected from along I-1 Pool.

Reed Canary Grass Locaitons, 1999.

We recommend repeated late spring or late autumn burning of the reed canary grass because it is confined to one 30 acre area and seeds of native species are present in the soil in and around it. Fire will allow native, fire-adapted species to compete successfully and a prescribed burn is the recommended method for removing reed canary grass (Hutchinson 1999). Hand removal is not feasible, herbicides are not selective enough, and heavy machinery would not destroy the hearty underground rhizomes. Annual burns may be necessary for 5-6 years. Seeding with native grasses and forbs after reed canary grass has died or gone dormant can also hasten the recovery of native species.

Multiflora Rose (Rosa multiflora)

Multiflora rose is a perennial shrub intolerant to shade characterized by long arching canes and flowers or fruits in a conspicuous cluster. Leaves are divided into 5-11 sharply toothed leaflets with a pair of fringed bracts at each leaf stalk base. The white, fragrant flowers are 2 cm wide and begin blooming in May or June. The rose hip fruits are bright red and form a conspicuous cluster that remains throughout the winter. These clusters make multiflora rose easily distinguishable from native roses that bear their fruits in clusters of 1-4 (NCPI 1999).

Imported from Japan in 1866, multiflora rose is an aggressive, prolific plant that can form dense thickets that crowd out native plants in the U.S. Intentionally planted for wildlife cover and as a barrier for livestock and automobiles, multiflora rose lives up to its reputation as a "living fence." It readily invades disturbed areas due to its high tolerance for a variety of conditions. It can spread by seed and by forming new plants at the tips of canes that touch the ground. The plentiful seeds (an average plant produces a million seeds per year) remain viable in the soil for up to 20 years and are readily dispersed by birds that enhance germination when the seed is passed through their digestive tract (NCPI 1999).

Multiflora rose is found in several scattered locations throughout the refuge. Large patches are found along the roads around the headquarters, along the eastern edge of C-2 Pool, along the southern edge of D-Pool, and along the southern edge of A-1 Pool. There are a few scattered plants on the eastern edge of D-Pool and the western end of C-1 Pool.

Mulitflora Rose Locaitons, 1999.
Mulitflora Rose Locaitons, 1999.

We recommend cutting of all plants 3-6 times per growing season for 2-4 years or treating them with herbicides. High mortality of multiflora rose has been achieved in this way (NCPI 1999). Plants should be flagged and rechecked due to the extreme longevity of seeds in the soil. The colder climate of the upper peninsula may aid in inhibiting the growth of some plants.

This preliminary survey reveals a serious infestation of glossy buckthorn at SNWR and potentially severe infestations by six other invasive exotic plants. Glossy buckthorn is replacing native species all around the refuge headquarters and visitor center and is marching into the wetlands, crowding out native fruit-bearing species like highbush cranberry (Viburnum opulus), raspberry (Rosa strigosus), arrow-wood (Viburnum dentatum), and nannyberry (Viburnum lentago). Left unchecked, glossy buckthorn could completely overtake the wetlands, lowering the water table and leaving little for the wildlife to eat. Ridding the refuge of glossy buckthorn should be a top priority at SNWR.

Five other invasive plants at SNWR could potentially pose severe problems for the refuge unless they are removed and continually monitored. Leafy spurge, purple loosestrife, tartarian honeysuckle, multiflora rose, and reed canary grass have posed severe problems elsewhere, yet at SNWR, these are found only in a few locations. Immediate removal of these plants and constant monitoring for any new plants is the best way to keep these plants from ever becoming a problem. The battle against invasives is much easier to win before a species becomes well-established.

Spotted knapweed poses a different sort of problem at SNWR. While it is widespread along the roads, shade intolerance seems to keep this species from moving past the roadsides. One exception is at two of the refuge hayfields. If these hayfields are to be maintained as quality wildlife habitat, spotted knapweed should be removed and replaced by competitive native species.

The majority of our recommendations involve manual removal, treatment with herbicides, and burning. While we considered it, we chose not to recommend biological control of these species. Biological control of spotted knapweed and leafy spurge is popular but we feel traditional methods (pulling, cutting, spraying) should be attempted first. Because the introduction of more exotics to control invasives is so risky, and SNWR is only just beginning to recognize and address the problem of invasive plants, all other methods should be exhausted before using biological controls.


Barnes, B.V. and W.H. Wagner. 1981. Michigan Trees. A Guide to the Trees of Michigan and the Great Lakes Region. University of Michigan Press: Ann Arbor, Michigan.

Devine, B. 1999. Clear-cut Mission. Communities Unite to Free Native Landscapes from the Grip of Invasive Species. The Nature Conservancy 49(4): 12-17.

Hutchinson, M. 1999. Vegetation Management Guideline. Reed Canary Grass (Phalaris arundinacea).

Native Plant Conservation Initiative. Alien Plant Working Group. 1999.

Schmidt, K.A. and C.J. Whelan. Exotic Lonicera and Rhamnus Increase Songbird Nest Predation: An Impetus for Ecological Restoration. In press.

Seney Annual Narrative Reports. 1989, 1991, 1995. Seney National Wildlife Refuge. United States Fish and Wildlife Service.

United States Department of Agriculture. 1994. Animal and Plant Health Inspection Service. Program Aid Number 59.

United States Fish and Wildlife Service. 1997. Region 3 Weed Information Book.

United States Forest Service, Hiawatha National Forest, et al. 1998. Michigan's Upper Peninsula Weeds. Collaborative brochure.

Voss, E.G. 1972. Michigan Flora. A Guide to the Identification and Occurrence of the Native and Naturalized Seed Plants of the State. Part I. Gymnosperms and Monocots. Kingsport Press: Bloomfield Hills, Michigan.

Voss, E.G. 1985. Michigan Flora. A Guide to the Identification and Occurrence of the Native and Naturalized Seed Plants of the State. Part II. Dicots. Kingsport Press: Bloomfield Hills, Michigan.

Voss, E.G. 1996. Michigan Flora. A Guide to the Identification and Occurrence of the Native and Naturalized Seed Plants of the State. Part III. Dicots Concluded. Kingsport Press: Bloomfield Hills, Michigan.

Westbrooks, R. 1998. Invasive Plants, Changing the Landscape of America: Factbook. Federal Interagency Committee for the Management of Noxious and Exotic Weeds (FICMNEW): Washington, DC.

Wisconsin State Cranberry Growers Association. 1999. Wisconsin Cranberry Weeds: Reed Canary Grass.


Table 1. Invasive exotic plants found on Seney National Wildlife Refuge.

Scientific NameCommon Name
Berberis thunbergiiJapanese Barberry
Bromus inermisSmooth Brome
Capsella bursa-pastorisShepard's Purse
Centaurea maculosaSpotted Knapweed*
Chrysanthemum leusanthemumOx-Eye Daisy
Cirsium arvenseCanada Thistle
Dactylis glomerataOrchard Grass
Daucus carotaQueen Anne's Lace
Euphorbia esulaLeafy Spurge*
Hieracium aurantiacumOrange Hawkweed
Hypericum perforatumSt. John's Wort
Linaria vulgarisButter-and-Eggs
Lolium perenneRyegrass
Lonicera tataricaTartarian Honeysuckle*
Lotus corniculataBird's Foot Trefoil
Malva moschataMusk Mallow
Lythrum salicariaPurple Loosestrife*
Melilotus albaWhite Sweet-Clover
Melilotus officinalisYellow Sweet-Clover
Nepeta catariaCatnip
Phalaris arundinaceaeReed Canary Grass*
Phleum pratenseTimothy
Plantago majorPlantain
Poa pratensisKentucky Bluegrass
Potentilla argenteaSilvery Cinquefoil
Prunella vulgarisHeal-All
Ranunculus acrisTall Buttercup
Rhamnus frangulaGlossy Buckthorn*
Rosa multifloraMultiflora Rose**
Sedum telephium (=purpureum)Live-Forever
Silene vulgarisBladder Campion
Sonchus arvensisField Sow-Thistle
Tragopogon pratensisYellow Goat's-Beard
Trifolium repensWhite Clover
Verbascum thapsusGiant Mullein

*Category one: highly invasive

**Category two: moderately invasive

Links to other invasive species sites:

U.S. Fish & Wildlife Service Invasive Species Program
Invasive Species in the Great Lakes Region
Great Lakes Environment - U.S.E.P.A
Landscaping with Native Plants - U.S.E.P.A