Black & pale swallow-worts

Black and pale swallow-worts, also known as “dog-strangling vines,” are perennial, herbaceous vines that grow from 2 to 6 1/2 ft in length. Native to Eurasia, these species are adapted to a variety of habitats where they out compete native species.

Impacts

  • Swallow-worts aggressively choke out desirable species. They are problematic in Christmas tree plantations, perennial crop fields, pastures, roadsides, disturbed areas, and natural areas.
  • Pure stands of pale swallow-wort suppress the establishment of other species and interfere with forest regeneration.
  • Related to milkweeds, swallow-worts are  toxic to livestock, deer and monarch butterfly larvae, which are sometimes fooled into laying their eggs on these plants, but their larvae do not survive.

Identification

Habitat: Both species of swallow-worts can be found in mixed hardwood forest to heavily shaded woods.  They also can be found in disturbed sunny areas, prairies, savannahs, open fields, and along roadsides in moist or dry soils.

Pale Swallow-wort (Cynanchum rossicum syn. Vincetoxicum rossicum)

Leaves:  Leaves are opposite in arrangement, oval to wedge-shaped with pointed tips. Generally, the leaves are 2.5″ to 4.5″ long and 2″ to 2.75″ wide, glossy and medium green in color. In summer, the leaves begin to display a warm, yellow color.

dog-strangling vine, European swallowwort, Vincetoxicum rossicum  (Gentianales: Asclepiadaceae) - 5492571

(Photo Credit: Rob Routledge, Sault College, Bugwood.org)

Flowers: The star-shaped flowers are small and fleshy, with 5 pink to reddish colored petals. They are borne in loose clusters and are visible in late May through mid-July.

dog-strangling vine, European swallowwort, Vincetoxicum rossicum  (Gentianales: Asclepiadaceae) - 5492570

dog-strangling vine, European swallowwort, Vincetoxicum rossicum  (Gentianales: Asclepiadaceae) - 5474087

(Photo Credit: Rob Routledge, Sault College, Bugwood.org)

Fruit: The fruit is a smooth, slender, pointed pod that looks much like a milkweed pod. The pods are light green in color and are frequently borne in pairs. They are abundant during July and August. Like milkweed, the pods open in late summer, disseminating large numbers of downy seeds. Can produce 2,000 seeds per square yard.

dog-strangling vine, European swallowwort, Vincetoxicum rossicum  (Gentianales: Asclepiadaceae) - 5392102

(Photo Credit: John M. Randall, The Nature Conservancy, Bugwood.org)

Black swallow-wort (Cynanchum louiseae syn. Vincetoxicum nigrum)

Similar to pale swallow-wort but leaves are dark green, shiny, 3-4″ long and 2-3″ wide. Flowers bloom in June to July and are dark purple. Black swallow-wort is native to Europe and escaped from a botanical garden in Massachusetts.

Control/Management

Prevention and Reporting: Once established, swallow-wort is difficult to control. Monitor for populations in late summer, when the plants turn golden yellow and pods are present.  Initial control efforts should concentrate on plants in sunny areas since they will produce the most seeds. Stay out of infested areas during seed dispersal to to prevent seed dissemination to unaffected areas. Likewise, clean boots, ATVs, and other equipment when coming out of infested areas.

Small patches can be dug out by hand. The entire plant must be removed and destroyed. To prevent seed dispersal, pods should be removed before they open and then burned.

Large stands can be managed  by consistent mowing when pods are very small (early July).  Controlled burning  is not effective and may improve site conditions for seedling establishment.

Triclopyr or glyphosate can be applied to foliage around mid-September.  Use of a surfactant helps herbicides penetrate the waxy leaf coating.  Cut-stem treatment with glyphosate is effective but labor intensive. Use of systemic “Round Up” herbicide is also effective in removing swallow-wort.

Areas of known infestation

Swallow-worts have been observed in nearly every county of New York, though a distinct epicenter exists in Jefferson County, where immense stands (100 to 500+ acres) of pale swallow-wort can be found on Grenadier Island and Stony Point in the town of Henderson. The plant is also established in the townships of Adams, Antwerp, Brownville, Cape Vincent, Clayton, Ellisburg, Henderson, Lyme, Orleans, and on Fort Drum.

Swallow-wort has slowly progressed outward from this epicenter. Management efforts are focused on preventing the spread toward Tug Hill and the Adirondacks and are therefore focused on Oswego Lewis, and Oneida counties.

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Select another species

Black & Pale Swallow-worts |   Giant Hogweed |  Purple Loosestrife |  Water Chestnut |Glossy Buckthorn |  Eurasian Water Milfoil |  Rock Snot, DidymoEuropean Frogbit | Japanese Knotweed