Invasive Plant Rogue's Gallery: Dog-Strangling Vine

by Jami Blaauw-Hara

If you've seen a twining vine with glossy, oval leaves, small pinkish/purple star-shaped flowers, and long pods later in the season that release silky, milkweed-like seeds, you've likely encountered dog-strangling vine.

The name actually refers to two invasive plants native to Eurasia: black swallowwort (Vincetoxicum nigrum) and pale swallowwort (Vincetoxicum rossicum). Most

common in the GTA is the pale swallowwort, featured in these photos.

Photo: Jim Natale, https://creativecommons.org/licenses/by-nc/4.0/

Photo: Don Sutherland, https://creativecommons.org/licenses/by-nc/4.0/

Photo: Tyler Smith, https://creativecommons.org/licenses/by-nc/4.0/

Dog-strangling vine is a perennial vine closely related to milkweeds. It is native to eastern Europe and was introduced to North America in the late 1800s. In its native habitat, its growth is controlled by specialist herbivores like the moth, Hypena opulenta, which lays its eggs almost exclusively on the leaves of dog-strangling vine. In fact, researchers at the University of Toronto are exploring using this moth to control the vine in Ontario: https://utoronto.scholaris.ca/items/54ec9edd-2491-4ea6-a21c-b18934ef8260

The vine forms dense monocultures of thick, nearly single-species carpets that exclude almost everything else. The roots release allelopathic chemicals that suppress nearby plant growth, much like garlic mustard (Alliaria petiolata).

Dog-strangling vine uses the same chemical strategy to prevent other plants from growing as garlic mustard (above) does. Photo: mireland616, https://creativecommons.org/licenses/by-nc/4.0/

Dog-strangling vine doesn’t just replace native plant species; it reshapes ecosystems. The vine reduces habitat for grassland birds like the threatened eastern meadowlark, suppresses forest regeneration by preventing native tree seedlings from establishing, and creates low biodiversity environments with fewer insects and pollinators. Even deer avoid it, increasing grazing pressure on native plants. 

Dog-strangling vine is crowding out other plants as it develops into a thick, tangled mat. Photo taken in Simcoe County, ON. Photo: Toby Rowland, https://creativecommons.org/licenses/by-nc/4.0/

Southern Ontario is especially vulnerable to dog-strangling vine because the plant loves disturbed soils (roadsides, trails, developments), old fields and abandoned lands, forest edges, and calcareous (limestone-rich) soils common in the region.

Because it's related to milkweed, monarch butterflies mistakenly lay eggs on it, but the leaves cannot support the larvae and the caterpillars starve. This makes it an

ecological sink for a species already in decline.

What can you do?

🔍Learn to identify its opposite oval leaves, twining vines, pink-maroon star-shaped flowers, and long pods that split open with silky seeds.

⛏Dig it up but don't pull it, as this leaves root fragments that resprout. Remove the entire root crown.

🌱Target small patches early when the populations are small and eradication is easier.

✂Cut or mow before seed pods form to reduce spread in larger patches.

✋Wear gloves--like milkweed, the sap can cause irritation in some people.

For more information, including a landowner's guide to controlling invasive woodland plants, see: https://www.ontario.ca/page/dog-strangling-vine.

You can also call the invasive wild species hotline to report sightings at 1-800-563-7711.