The Nottawasaga Valley Conservation Authority

Dog Strangling Vine

What is Dog Strangling Vine?

Dog Strangling Vine (Cynanchum rossicum) is one of Ontario’s most unwanted invasive plants. 

Also known as black swallowwort or pale swallowwort, dog-strangling vine does not actually strangle dogs but it can “strangle” native plants and small trees if it is in dense patches. This plant was first observed in Ontario in the late 1800s, and is originally native to Eurasia.

  • Leaves are oval shaped with a pointed tip arranged oppositely on the stem, and can be 5-10 cm long.
    The leaves are a glossy green in spring and turn yellow in late summer.
  • Flowers are a pink-maroon colour and very small, and they are randomly placed throughout the vine.
  • Fruiting seed pods start to form in July, producing white fluffy seeds in late summer.
  • The vine is found commonly in disturbed areas like highways, railways, Christmas tree plantations, nursery and perennial crop farms, and abandoned pastures. 
Dog Strangling Vine

Where is Dog Strangling Vine found in our watershed?

Dog-strangling vine is beginning to invade the NVCA watershed. It is most common south of Highway 89. It is also present along portions of the Collingwood shoreline—near globally rare coastal marshes. A small patch in the internationally significate Minesing Wetlands. NVCA has monitored the locations where dog-strangling vine is found while the County of Simcoe and the Nature Conservancy of Canada has made efforts to control the spread of the invasive species.

Why is it of concern?

Dog-strangling vine grows and spreads very quickly. It can invade forests and create dominate ground covers. The vine can attach to small trees and plants and climb up to 2 m high. Dense clusters can displace native plants and alter the forest ecology, and even the forest birds present.

Its seeds are fluffy and white, similar to milkweed, and can be easily distributed in disturbed areas by wind. As well, the predicted threatened monarch butterflies are thought to be impacted by dog-strangling vine. These butterflies will sometimes lay their eggs on the vine thinking it is milkweed and the larvae consequently do not survive.

How to control the spread

On your property:

  • Removal of dog-strangling vine is quite difficult once established.
  • Ideally, digging out the root of a first year established plant will prevent its spread. 
  • Care must be taken to remove the entire root since plants can re-sprout from any remaining rootstock.
    Once dog-strangling vine has reached the second year of growth, the roots are developed and strong and are more difficult to remove manually. 

See The Landowner’s Guide to Controlling Invasive Woodland Plants for more information on controlling Dog Strangling Vine on your property. 

When you are enjoying nature:

Remember to clean your shoes after hiking and keep pets on a leash to avoid further spread.

Early detection is key

Early detection and rapid response is essential for the control and/or eradication of invasive species in an area. If you spot Dog Strangling Vine, please report the sighting to EDDmapS.

More information

Invasive species on private property

NVCA does not offer a service to remove invasive species on private property.  If you are looking for tips on dealing with invasive species on your property, see the links above, or visit Ontario’s Invading Species Awareness Program.

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