Cynanchum rossicum and Cynanchum louiseae
What Ontario is Doing
To prevent the further spread and introduction of these unwanted invaders in the province, Ontario has regulated Dog-strangling Vine and Black Dog-strangling Vine as restricted under the Invasive Species Act. For more information on the Invasive Species Act and Regulations visit www.ontario.ca/invasionON.
The name “Dog-strangling Vine” refers to two invasive plants native to Eurasia– black swallowwort and pale swallowwort. These look-alike members of the milkweed family were introduced to the northeastern United States in the mid-1800s for use in gardens. In recent years these perennial vines have spread rapidly throughout central and southern Ontario. Because they are so similar, both species have the same common name.
Dog-strangling Vine prefers open sunny areas, but can grow well in light shade. It grows aggressively up to two metres high by wrapping itself around trees and other plants, or trailing along the ground. Dense patches of the vine can “strangle” plants and small trees.
The plant can produce up to 28,000 seeds per square metre. The seeds are easily spread by the wind, and new plants can grow from root fragments, making it difficult to destroy. The vine has invaded ravines, hillsides, fence lines, stream banks, roadsides and utility corridors. Dog-strangling Vine is also found in prairies, alvars (limestone plains), plantations of pine trees and natural forests.
Dog-strangling Vine was first found in Ontario in the late 1800s. Outside its native range, Dog-strangling Vine is now found in parts of Ontario, southern Quebec and several American states.
Impacts of Dog-Strangling Vine
- Dog-strangling Vine forms dense stands that overwhelm and crowd out native plants and young trees, preventing forest regeneration.
- Colonies form mats of interwoven vines that are difficult to walk through and interfere with forest management and recreational activities.
- Leaves and roots may be toxic to livestock. Deer and other browsing animals also avoid dog-strangling vine, which can increase grazing pressure on more palatable native plants.
- The vine threatens the monarch butterfly, a species at risk in Ontario. The butterflies lay their eggs on the plant, but the larvae are unable to complete their life cycle and do not survive.
How to Identify Dog-Strangling Vine
- Grows one to two metres high by twining onto plants, trees or other structures.
- Leaves are oval with a pointed tip, seven to 12 centimetres long, and grow on opposite sides of the stem.
- Pink to dark purple star-shaped flowers have five petals about five to nine millimetres long.
- The plant produces bean-shaped seed pods four to seven centimetres long that open to release feathery white seeds in late summer.
What You Can Do
- Learn how to identify these species of dog-strangling vine and how to avoid accidentally spreading these invasive plants. This is especially important if you are planning to do work in an area which contains dog-strangling vine.
- Learn how to effectively manage dog-strangling vine on your property. The guide to Best Management Practices for dog-strangling vine describes the most effective and environmentally safe control practices for this species.
- Never buy or plant dog-strangling vine. It is against the law to buy, sell, trade or purposely grow dog-strangling vine.
- Stay on designated trails and keep pets on a leash. Leaving trails or entering areas containing dog-strangling vine can encourage the spread of this plant.
- When leaving an area containing dog-strangling vine, inspect, clean and remove mud, seeds and plant parts from clothing, pets (and horses), vehicles (including bicycles and ATVs), and equipment such as mowers and tools.
- Do not compost dog-strangling vine in your backyard composter. Seeds could survive and grow in compost, unless high enough temperatures are reached to kill the reproducing structures. Contact your local municipality to determine if plant material can be brought to their composting facility. Ontario composting facilities monitor the compost process and meet provincially regulated temperature requirements.
- If you have any information about the illegal importing, distribution or sale of dog-strangling vine, report it immediately to the MNRF TIPS line at 1-877-TIPS-MNR (847-7667) toll-free anytime. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).
- If you’ve seen dog-strangling vine or other invasive species in the wild, please contact the toll free Invading Species Hotline at 1-800-563-7711, or visit EDDMapS Ontario website to report a sighting.
- Ontario Invasive Plant Council
- Ontario Ministry of Natural Resources and Forestry
- Ontario Ministry of Agriculture, Food and Rural Affairs – Ontario Weeds
- Invasive Species Centre
OFAH/OMNR Invading Species Awareness Program. (2012). Dog-Strangling Vine. Retrieved from: http://www.invadingspecies.com. This factsheet may be reproduced for non-commercial purposes.