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FACT SHEET: PALE SWALLOW-WORT

Pale Swallow-wort 

Cynanchum rossicum (Kleopov) Barbarich 

Milkweed family (Asclepiadaceae) 

NATIVE RANGE 

Europe 

DESCRIPTION 

Pale or European swallow-wort (previously Vincetoxicum rossicum) is a 

long-lived perennial, twining herbaceous vine. The leaves are oval 

shaped with pointed tips, 3-4 in. long by 2-3 in. wide, and occur in pairs 

along the stem. The small five-petaled, star shaped flowers are creamy 

pink to reddish brown, about 1⁄4 in. across, and are borne in clusters. The 

fruits are slender tapered pods, 2-3 in. long by about 1⁄4 in. wide, that turn 

from green to light brown as they mature. When ripe, the fruits open 

along a seam and release flattened seeds equipped with a downy 

parachute that aids in wind dispersal. In contrast to its invasive relative the black swallow-wort (C. louiseae), pale swallowwort does not have rhizomes. Plants tend to grow in clumps of several to many stems, forming extensive patches. 

NOTE: There are many native species of Cynanchum, including honeyvine (Cynanchum laeve) which occurs throughout 

the eastern U.S. and could be confused with pale swallow-wort. Honeyvine has white flowers, and its leaves have a 

distinct heart-shaped base. 

ECOLOGICAL THREAT 

Pale swallow-wort can form extensive patches that crowd out native plant species and have various impacts on native 

wildlife. In some instances old-field habitats occupied by goldenrods and grasses are replaced almost exclusively by 

swallow-wort, disrupting natural succession and completely altering the physical structure of those habitats. A New York 

study on grassland birds indicated that as swallow-wort cover increases, grassland bird presence declines. In a study of 

ground and stem-dwelling insects in Ottawa, Ontario, diversity of these insects was found to be lower in pale swallow-wort 

infestated areas than in non-invaded old-field sites and gall-makers and miners were completely absent. In New York, 

pale swallow-wort is displacing the federally listed Hart's tongue fern (Asplenium scolopendrium) at one site and poses a 

threat to additional populations in the state. Globally rare alvar habitats (limestone pavement barrens supporting unique 

plant communities) in New York are also threatened by expanding swallow-wort populations. Research indicates that pale 

swallow-wort modifies the soil microbial community, displacing native plant species that are adapted to the unique 

microbial associations of alvar. 

DISTRIBUTION IN THE UNITED STATES 

Pale swallow-wort has been reported to be invasive in natural areas in New 

Hampshire, New York, Rhode Island and Wisconsin. Small occurrences or 

infestations have been also been reported for urban areas in Pennsylvania, 

Maryland, and Indiana, presumably due to escapes from backyards and 

landscaped areas. 

HABITAT IN THE UNITED STATES 

Pale swallow-wort is associated exclusively with upland areas and is tolerant of 

a range of light and moisture conditions. Typical habitats include old fields, 

hedgerows, brushy areas and woodlands. Both natural and human-caused 

disturbance including ice-scoured river banks, talus slopes, transportation corridors, quarries and abandoned agricultural 

fields provide acceptable habitats. Pale swallow-wort is particularly competitive in areas with shallow soils over limestone 

bedrock that can be prone to summer droughts. There appears to be a distinct association with limestone soils. Pale 

swallow-wort can be a serious problem in perennial cropping systems such as pastures and Christmas tree plantations 

and has been noted in no-till corn fields in central New York State. It is not a weed of turf or annual crops. 
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BACKGROUND 

Pale swallow-wort was likely introduced for ornamental purposes and was first collected in Monroe and Nassau counties 

in New York State in 1897. Subsequent records of occurrences include: Massachusetts (1919), Pennsylvania (1927), New 

Jersey (1938), Connecticut (1942), Indiana (1961), New Hampshire (1979) and Michigan (1985). Indications of naturalized 

populations include records of collections from roadsides (1897, 1917) and natural areas (1918, 1919 and 1921) in New 

York State. 

BIOLOGY & SPREAD 

Pale swallow-wort emerges in spring and flower from June to July followed by production of fruits (pods) which is directly 

related to the level of light available. The flowers are self-pollinating and it spreads primarily by seed. Thick infestations in 

full sun can produce up to 2,000 seeds per square meter. The seeds are polyembryonic (i.e., having one to four embryos 

per seed) which greatly increases the potential for establishment. Wind dispersal of seed occurs from late July and 

continues into the fall. Populations growing under dense wooded canopy may have inadequate resources to produce 

flowers or seeds. Pale swallow-wort dies back to the ground every winter. Pale swallow-wort root crown fragments 

support dormant buds that readily sprout if not destroyed. 

MANAGEMENT OPTIONS 

As with all invasive species, early detection and removal is the best approach for preventing the establishment and spread 

of this plant. If you find some black swallow-wort, look for more, and aim to 

remove all plants at a site. Stay out of patches that are actively dispersing 

seeds, unless you plan to collect and dispose of the seeds carefully. Clean all 

machinery that has traveled through swallow-wort patches that have maturing 

or dispersing pods. For large established infestations, chemical control is the 

most effective means. 

Biological 

There are no biological controls available for this plant. 

Chemical 

Two systemic herbicides - Garlon® 4 (triclopyr ester) and Roundup Pro® 

(glyphosate) – have been found to be effective in controlling pale swallow-wort. 

These herbicides should be applied when plants are actively growing, after 

flowering has begun. DO NOT SPRAY TOO SOON. Avoid the temptation to 

spray the plants as soon as they emerge in May. Only when the plants flower 

will they be large enough to receive enough spray on the exposed leaf surface 

to deliver a killing dose to the roots. Plants that are sprayed before pods form 

will probably not produce a viable seed crop that season. Be patient. Systemic 

herbicides do not cause a “burn down” of plants like contact herbicides do. 

Within 1-2 weeks the plants will look sick. There may be dead tissue spots on 

most leaves many yellowing leaves. Do not waste herbicide, money or effort by 

spraying plants twice. Sick plants cannot effectively absorb the herbicide 

through the leaf surface or move the herbicide to the roots. Swallow-wort 

control may take a few years and it is important not to use more herbicide than 

is necessary. 

Cut stem application 

For cut stem applications use a 50 to 100% solution of herbicide concentrate. Roundup Pro® is much more effective than 

Garlon® 4 for cut stem application. Apply the herbicide solution immediately to cut stem surfaces. As mentioned above 

with foliar applications, if treated plants have mature pods the seeds may ripen after treatment and disperse, leading to 

new infestations. If possible, cut plants low and bag and dispose of the portions with pods. 

Foliar application

Experience shows that foliar sprays of systemic herbicides (i.e., herbicides absorbed into the plant and carried internally) 

only kill plants in the upper layers of the infestation, requiring repeated applications to effectively control the entire mass. It 

is important to treat plants before pods begin to form to ensure that viable seeds are not produced. If that is not possible, 

plants with pods should be cut or mowed first and then sprayed once they regrow. Regrowth will be rapid in summer. 
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Herbicide application to the new growth should be conducted from August through early September. If mowing is not 

possible, for example in wooded areas, cut plants by hand just below the lowest pods, and spray the new growth. In 

situations where foliar sprays are undesirable, for example when desirable native plants or other non-targets would be 

harmed, sponging the herbicide on individual plants, using the same concentration as foliar sprays is an option. 

Manual 

Remove pod-bearing plants from the site and destroy them. Eradication on a small scale must be very thorough and 

requires dedication. The complete root crown must be dug out before the seeds ripen. Plants bearing seeds should be 

burned or bagged and disposed of in a landfill. Infested land might be brought under control by plowing and planting an 

annual crop until the seed soil bank is depleted, possibly as long as five years. 

Mechanical 

Mowing, even several times a year, will not eradicate swallow-wort however, it can be employed to prevent a seed crop. 

Cutting is most effective at preventing a mature seed crop if done in early to mid-July, when there are small, immature 

pods on the plants. Cutting during the flowering period but before pod formation will allow plants to recover and still 

produce a viable seed crop. Monitor mowed areas and mow a second time if pods reach mature size in late summer or 

early fall. Hay cutters can contribute to the spread of swallow-wort if cutting is not timed correctly. Hay crops infested with

swallow-wort and then sold elsewhere can be a means of introducing swallow-wort to new areas. 

USE PESTICIDES WISELY: Always read the entire pesticide label carefully, follow all mixing and application instructions and wear all 

recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use 

requirements, restrictions or recommendations. 

NOTICE: mention of pesticide products on this page does not constitute endorsement of any material.

RESTORATION 

Rehabilitation efforts will vary by habitat and age of infestation. Young infestations may have enough of the enduring seed 

bank and dormant plants of the displaced plant community to recover without active management. In degraded habitats, 

establishing cool season grasses will permit application of broad leaf herbicides to control swallow-wort plants recruited 

from the seed bank and from nearby infestations. Research on restoration of swallow-wort infested areas is on-going. 

CONTACTS 

For more information on the management of pale swallow-wort, please contact: 

• Fran Lawlor, Swallow-wort Management Coordinator, Central and Western New York Chapter, The Nature 

Conservancy, 269 Ouderkirk Rd., Pulaski, NY 13142; (315) 387-3600, fax: (315) 387-3602, flawlor at tnc.org 

• Sandra Bonanno, Stewardship Ecologist, Central and Western New York Chapter, The Nature Conservancy, 269 

Ouderkirk Rd., Pulaski, NY 13142; (315) 387-3600, fax: (315) 387-3602, sbonanno at tnc.org 

SUGGESTED ALTERNATIVE PLANTS 

In the eastern U.S., the native honeyvine (Cynanchum laeve) can be substituted for the invasive pale swallow-wort. Other 

attractive native vines that are widely available in the East include trumpet creeper (Campsis radicans), trumpet 

honeysuckle (Lonicera sempervirens), Dutchman’s pipe (Aristolochia macrophylla), Virginia creeper (Parthenocissus 

quinquefolia) and native wisteria (Wisteria frutescens). Check with your state or local native plant society for more 

information on alternative species and sources where you can obtain them. 

OTHER LINKS 

• http://www.invasive.org/search/action.cfm?q=Cynanchum%20rossicum 

• http://nbii-nin.ciesin.columbia.edu/ipane/icat/browse.do?specieId=14

AUTHOR 

Fran Lawlor, Central and Western New York Chapter, The Nature Conservancy, Pulaski, NY 

REVIEWERS 

Gerry Rising and Ann Rhoads 
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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

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EDITOR

Jil M. Swearingen, National Park Service, Washington, DC 

PHOTOGRAPHS 

©John M. Randall/The Nature Conservancy 

REFERENCES 

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seed dispersability and seed quality. Am. Mid. Nat. 148: 263-270. 

Casagrande R. A. and Dacy, J. 2001. Monarch Butterfly (Danaus plexippus) oviposition on Black Swallowort 

(Vincetoxicum nigrum). Rhode Island Nat. Hist. Surv. 8: 2-3. 

Christensen, T. 1998. Swallow-worts, the ecology and control of Vincetoxicum spp. Wildflower: 21-25. 

DiTommaso A. and Losey, J. E. 2003. Oviposition selection and larval feeding by Monarch Butterflies on two invasive 

swallow-wort species. Proceeding of the Annual Meeting of the Northeastern Weed Science Society of America 

57:121. 

Ernst, C. and Cappuccino, N. 2003 The effects of an invasive vine, Vincetoxicum rossicum, (Asclepiadaceae) on old-field 

arthropod assemblages in Ottawa, Ontario. (Talk) New England Invasive Plant Summit, September 19-20, 2003, 

Framingham, Massachusetts 

Greipsson, S. and DiTommaso, A. 2002. Impact of the invasive plant Vincetoxicum rossicum on activity of arbuscular 

mycorrhizal fungal populations. Ecological Society of America Meeting Abstracts 87: 358. 

Haribal, M. and Renwick, J.A.A. 1998. Identification And distribution of oviposition stimulants for Monarch butterflies in 

hosts and nonhosts. J. Chem Ecol. 24: 891-904. 

Lawlor, F. M. 2000. Herbicidal treatment of the invasive plant Cynanchum rossicum and experimental post control 

restoration of infested sites. M.S. Thesis, State University of New York College of Environmental Science and 

Forestry, New York. 

Lawlor, F.M. and Raynal, D.J., 2002. Response of swallow-wort to herbicides. Weed Science 50:179-185. 

Lumer, C. and S. E. Yost. 1995. The reproductive biology of Vincetoxicum nigrum (L.) Moench (Asclepiadaceae), a 

Mediterranean weed in New York State. Bulletin of the Torrey Botanical Club 122:15-23. 

Markgraf, F. 1972. Vincetoxicum N .M. Wolf. Pages 71-73 in T.G. TUTIN, v. h. Heywood, N. A. Burgess, D.H. Valentine, 

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Moore, R.J. 1959. The dog-strangling vine Cynanchum medium, its chromosome number and its occurrence in Canada. 

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Pobedimova, E. G. 1952. Family CXXXIII Asclepiadaceae Lindl. Pages 487-527 in B. K. Shiskin and E. G. Bobrov, eds. 

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Sheeley, S. 1992. The distribution and life history characteristics of V. rossicum (Vincetoxicum rossicum). M.S. Thesis, 

State University of New York College of Environmental Science and Forestry, 

Sheeley, S. E. and D. J. Raynal. 1996. The distribution and status of species of Vincetoxicum rossicum in eastern North 

America. Bulletin of the Torrey Bot. Club 123(2):148-156. 
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Plant Conservation Alliance®s Alien Plant Working Group 

Xeeds HoneXild: Alien Plant Invaders of Natural Areas 

http://www.nps.gov/plants/alien/

Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: Pale Swallow-wort 

(Cynanchum rossicum). http://www.invasive.org/weedus/subject.html?sub=4260. 

USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 

70874-4490 USA.