PAGE

Home / Weed identification / Pale Swallow-Wort

US weed ID · Invasive vine

Pale Swallow-Wort

Vincetoxicum rossicum · Asclepiadaceae (milkweed family)

Perennial
Twining vine
Non-native
Toxic / hazard

A twining vine with glossy, opposite, heart-shaped leaves, small star-shaped pinkish-burgundy flowers and skinny milkweed-like pods, smothering a field edge or woodland floor? That is very likely pale swallow-wort.

How to get rid of it All weeds A–Z

Pale Swallow-Wort (Vincetoxicum rossicum) growing — weed identification photo — Photo: Rob Routledge, Sault College, Bugwood.org · CC BY 3.0 · Wikimedia Commons

Safety warning

Considered toxic to livestock. Minnesota's risk assessment reports that the roots contain hemolytic glycosides, a goat died in a feeding trial, sheep avoid grazing it, and some horse owners have given up infested pastures. UConn notes it contains toxins harmful to some native insects and mammals. It is also a deadly trap for monarch butterflies, whose caterpillars cannot survive on it. The same review says it is not a serious threat to human health.

Quick ID

Twining vine with opposite, glossy, smooth-edged leaves
Small star-shaped flowers, dull pink to burgundy
Slim, smooth milkweed-like pods in summer
Clear, watery sap, not milky
Downy stems rising in clumps from a root crown

Fact sheet

Scientific name: Vincetoxicum rossicum
Family: Asclepiadaceae (milkweed family)
Also called: European swallow-wort
Life cycle: Perennial
Native to the US?: No. Native to eastern Ukraine and southwestern Russia. USDA PLANTS lists it as introduced in the lower 48 states and Canada.
Height: A twining vine usually 3 to 6.5 feet long (UConn reports up to about 9) that climbs other plants or sprawls in clumps.
Leaves: Opposite, smooth-edged, glossy dark green leaves, oval to heart-shaped with a pointed tip, about 2 to 5 inches long. They turn bright yellow as they dry.
Flowers: Small, flat, star-shaped flowers with five petals, dull pink to deep burgundy, in clusters where the leaves meet the stem, blooming in early summer.
Seeds / fruit: Slender, smooth, milkweed-like pods 1.5 to 3 inches long that split in late summer and fall, releasing flat brown seeds with white silky tufts.
Roots: A stout root crown just below the soil surface, packed with buds, plus thick, fleshy roots. Some plants also form short rhizomes.
Spreads by: Mainly by wind-blown seed, which can travel about 60 meters (roughly 200 feet), and by new shoots from the root crown.
Where you’ll find it: Old fields, pastures, roadsides and ditches, woodlands (even dense shade), brushy areas, tree farms, no-till fields, gardens and urban areas.
When you’ll see it: Shoots come up from the root crown in spring, flowers open in early summer, pods form from mid to late summer and split to release seed into fall, and the top growth dies back in winter.
Toxicity: Considered toxic to livestock. Minnesota's risk assessment reports that the roots contain hemolytic glycosides, a goat died in a feeding trial, sheep avoid grazing it, and some horse owners have given up infested pastures. UConn notes it contains toxins harmful to some native insects and mammals. It is also a deadly trap for monarch butterflies, whose caterpillars cannot survive on it. The same review says it is not a serious threat to human health.
Legal status: Not on the federal noxious weed list. Minnesota lists it as a Prohibited (Eradicate) noxious weed and Massachusetts includes it on its Prohibited Plant List. Minnesota's risk assessment notes several other states also regulate it, so check your state's list.
Difficulty to control: Very hard
Best time to act: Dig root crowns of small patches in spring and early summer, before pods form. Time herbicide around flowering to early pod formation (about June), with a follow-up in late summer. Never let pods ripen and split.

What is pale swallow-wort?

Pale swallow-wort is an invasive, herbaceous vine in the milkweed family from eastern Europe, likely brought over as an ornamental and first recorded in the United States in New York in 1891. USDA PLANTS lists it as Cynanchum rossicum. Early pale swallow-wort identification matters because the plant looks harmless at first, a modest vine with glossy leaves and small pinkish flowers, yet it can carpet old fields and woodland floors so thickly that little else survives underneath.

Once established it is hard to stop. Each plant grows from a tough, budded root crown that resprouts after cutting, and dense stands can release thousands of wind-borne seeds per square meter each year. It crowds out native plants, has been tied to fewer grassland birds and insects, and invades rare limestone alvars. It is hard to control in no-till corn and soybeans, it is toxic to livestock, and it lures monarch butterflies into laying eggs on a plant their caterpillars cannot survive.

Pale Swallow-Wort identification: what to look for

Look for a vine that twines rather than one that clings with tendrils or rootlets, with paired leaves and small star-shaped flowers in early summer. Break a leaf or stem: swallow-wort sap is clear, while true milkweeds bleed white latex. Then check flower color to separate pale swallow-wort from its close cousin, black swallow-wort.

Leaves: Opposite, smooth-edged and glossy dark green, oval to broadly heart-shaped with a pointed tip, about 2 to 5 inches long. They yellow brightly as they dry.
Stems: Thin, twining, downy stems that wrap around fences, shrubs and other plants. They grow in clumps from a single crown, break easily when pulled, and die back to the ground each winter.
Sap: Clear and watery when a stem or leaf is broken. Milkweeds have milky white sap.
Flowers: Small, flat, five-petaled stars in clusters at the leaf bases in early summer, dull pink to deep burgundy. Black swallow-wort flowers are dark purple with shorter, triangular petals.
Pods: Smooth, slender pods about 1.5 to 3 inches long, ripening from green to brown and splitting to release brown seeds with white silky tufts.
Roots: A thick, many-budded crown just below the surface with fleshy roots. Leave a piece behind and it regrows.

Pale Swallow-Wort (Vincetoxicum rossicum) — identification photo — Photo: Rob Routledge, Sault College, Bugwood.org · CC BY 3.0 · Wikimedia Commons

Where it grows in the United States

Pale swallow-wort is most common in the Northeast. UConn Extension reports it mainly in Connecticut, Massachusetts, Rhode Island and New York, with scattered populations in Michigan and Illinois, and Minnesota found its first reproducing infestations in Scott County in 2020 and 2021. USDA PLANTS lists it as introduced in both the lower 48 states and Canada.

It is not fussy about site. Look for it in old pastures and fields, road ditches and roadsides, brushy edges, gardens, meadows, urban areas, tree farms and no-till crop fields. It also handles shade and can take over a woodland understory. It tolerates drought and short floods and does especially well on shallow soils over limestone. New patches usually start from wind-blown seed, then thicken as each crown sends up more stems.

Pale Swallow-Wort look-alikes

A few plants get mixed up with it:

Black swallow-wort (Cynanchum louiseae): Its closest relative, with the same twining habit, glossy opposite leaves and slim pods. Black swallow-wort flowers are dark purple with short, triangular petals and a yellowish center; pale swallow-wort flowers are dull pink to burgundy with slightly longer petals. Both are invasive and controlled the same way.
Common milkweed (Asclepias syriaca): A native, upright plant up to about 5 feet tall that does not twine. It has broad oval leaves, round clusters of light pink flowers and milky white sap, and it is a key food plant for monarchs. Swallow-wort has clear sap and climbs.
Rough potato (Metaplexis japonica): Another twining vine, native to eastern Asia, but it grows much longer, up to about 25 feet, with heart-shaped leaves and pale pink flowers whose petals curl back.

How to get rid of pale swallow-wort

Pulling, digging and mowing: Small, new patches are worth digging. Loosen the soil and lift each plant with its whole root crown; stems snap if you just pull, and any crown left behind resprouts. Expect to revisit the spot once or twice a season for years. Mowing alone will not kill it, and Minnesota advises against routine mowing because it can spread seed and root pieces; if you cut to stop seed, UConn suggests doing it after flowering as pods begin to form, typically late June to early July, and repeating, knowing crowns may regrow thicker. On small sites, pick pods before they split. Never compost or leave crowns, roots or pods on the ground; bag them for the landfill, and clean equipment and boots before leaving the site.

Cultural control matters most, because the right conditions keep it from coming back.

Do not plant it, and clean soil and plant debris off equipment before leaving infested sites.
After control, reseed bare ground with competitive native grasses; Minnesota's review notes prescribed fire plus native grass seeding has helped in some programs.
Plan for several years of work and check every spring and summer for seedlings and resprouts.
Annually cultivated fields tend to keep it out; it is mainly a problem in no-till fields, pastures and unmanaged ground.
A biological control moth was approved in 2018 and released in New England and New York, but it is not available to homeowners.

Herbicides: UMN and UConn Extension both list glyphosate and triclopyr, and UMN adds imazapyr. Spot-spray the leaves around flowering, about June, before seed pods mature, and plan a second application later in the season; UConn suggests a follow-up glyphosate treatment in August. Minnesota's review found that glyphosate at early flowering and triclopyr at early pod formation each cut swallow-wort cover substantially in a study, but treatments on small, young plants can leave roots alive to resprout. For small patches, cut the stems and treat the cut ends right away. Large infestations usually need herbicide for several years in a row. Glyphosate and imazapyr are nonselective and will injure other plants they contact. Use only a product labeled for your site. The label is the law. If you hire someone to spray, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Keeping it from coming back

The best time to stop pale swallow-wort is before it seeds. If you see a single plant or small clump, dig it out, crown and all, and bag it. Clean mowers, tillage tools, boots and tires after working in infested areas, and avoid moving fill or mulch from sites where it grows.

Because the seeds blow in from neighboring properties and roadsides, watch fence lines, ditches and woodland edges each summer. If you find it, report it to your state's invasive species or agriculture program. In states where it is regulated, such as Minnesota, sightings are tracked and the plant may be targeted for eradication.

Questions we get about pale swallow-wort

Is pale swallow-wort a milkweed?

It is in the same broad group and has similar pods and silky seeds, but it is not a true milkweed. It twines, has clear sap, and is a dead end for monarch caterpillars rather than a food plant.

Is pale swallow-wort poisonous to livestock?

It is considered toxic. Minnesota's risk assessment reports hemolytic compounds in the roots, a goat death in a feeding trial and pastures abandoned by horse owners.

Should I mow pale swallow-wort?

Not as your main tactic. Mowing does not kill the crowns and can spread seed and root pieces. If you cut to stop seed, do it as pods start to form, repeat it, and combine it with digging or herbicide.

How do I tell pale swallow-wort from black swallow-wort?

Check the flowers in early summer: pale swallow-wort is dull pink to burgundy with slightly longer petals, black swallow-wort dark purple with short triangular petals.

Weeds taking over a bed, slope or wet spot?

In central Pennsylvania, Muthler rebuilds beds, regrades and drains wet ground, clears overgrown brush and builds patios and walls across Clinton, Lycoming, Centre and Union counties. Outside central PA? Groundwork Single Space ($349) is a scaled 2D plan of one area with plants matched to your hardiness zone, designed remotely.

Get a free estimate See landscape design

Similar weeds

Black Swallow-wortVincetoxicum nigrum

Air PotatoDioscorea bulbifera

Chinese WisteriaWisteria sinensis

Photos: Wikimedia Commons contributors, credited under each photo (used under their Creative Commons or public-domain licenses).
Sources: Minnesota Noxious Weed Risk Assessment: Pale Swallow-wort (Minnesota Department of Agriculture) · University of Minnesota Extension: Pale swallow-wort · UConn Extension: Black and Pale Swallow-wort invasive plant factsheet · Massachusetts Department of Agricultural Resources: Massachusetts Prohibited Plant List · USDA PLANTS: Cynanchum rossicum (European swallow-wort) · USDA APHIS: Federal Noxious Weed List
Herbicides: always read and follow the product label. Pesticide applicator licensing rules vary by state.

← Back to all weeds A–Z