Tree Killers: Dog-Strangling Vine

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  • Common English name: Dog-Strangling Vine
  • Other names: swallowwort, pale swallowwort, black swallow-wort, Louise’s swallow-wort, black dog-strangling vine
  • Latin (scientific) name: Cynanchum spp. or Vincetoxicum spp.

Threat type

150x150 plants

History in Canada

  • Dog-strangling Vines were brought to North America from Europe in mid- to late-1800’s as ornamentals
  • two species are established and spreading rapidly in Canada: Pale Swallow-wort (Cynanchum rossicum) and Black Swallow-wort (Cynanchum louiseae)
  • both species are most abundant in southern Ontario but also occur in adjacent Quebec. There is an old record of Pale Swallow-wort from British Columbia but it has not become established there yet


  • a perennial vine with opposite leaves that belongs to the Milkweed family
  • small purplish flowers develop into narrow pods with many seeds
  • spreads mainly by wind-born seeds to produce large dense patches
    in open habitats, the vines may be less than one metre tall (three ft) but in woods and rich soil, vines may become 2.5 m (eight ft) tall and blanket shrubs and small trees
  • tolerates a wide range of upland habitats including forests and woodland edges
  • generally restricted to areas with limestone bedrock

Impact on Trees

  • grow in dense patches that suppress native tree seedlings and young saplings due to heavy shade

What can be done to control this tree killer?

  • primarily with herbicide application and several treatments are needed
  • mechanical control is very difficult due to the deep root system and abundant seed production

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