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Invasive Species |
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Tree Killers
Dog-strangling Vine or Swallow-wort
(Cynanchum spp. or Vincetoxicum spp.)
 Photo 8: John M. Randall/The Nature Conservancy Biology
- 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
 Photo 9: Bill Jacobs/The Nature Conservancy 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
Impact on Trees
- grow in dense patches that suppress native tree seedlings and young saplings due to heavy shade
 Photo 10: John M. Randall/The Nature Conservancy Control
- primarily with herbicide application and several treatments are needed
- mechanical control is very difficult due to the deep root system and abundant seed production
- no biological controls have been developed
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