Dog-strangling Vine and Black Swallowwort (Vincetoxicum rossicum and V. nigrum)
Dog-strangling Vine (Vincetoxicum rossicum, also known as European swallowwort) and Black Swallowort (Vincetoxicum nigrum) are invasive perennial herbaceous vines1. Both species are native to Europe and have become invasive in North America since their introduction in the mid 1800s2. Dog-strangling vine is found in isolated locations within the Credit River Watershed. It is listed under the Noxious Weed in Ontario list and is listed as a restricted species under the Invasive Species Act.
Dog-strangling Vine (DSV) is a member of the milkweed family and it typically grows 1 – 2 meters in height, forming dense mats by twining onto trees, other plants, and even itself2. It prefers sunny, open areas but will also grow in filtered shade. DSV is tolerant of a wide variety of growing conditions and can be found in forests, thickets, meadows, and roadsides. The leaves are yellowish-green to dark green in color, opposite, and oval to oblong in shape. DSV flowers in late June, producing small clusters of flowers at the tip of the stems and where the leaves join the stem. Flower colour differs between the two species, with V. nigrum having purple-brown to dark purple flowers and V. rossicum having pink flowers.
Dog-strangling Vine leaves
The fruit of DSV are 4 – 6 cm long pods that split open in August, to release numerous white fluffy seeds (similar to a Common Milkweed seed pod)2. The seeds are dispersed by wind and can travel long distances. Reproduction is achieved both by seed dispersal and vegetatively by rhizomes and shoots from the root crown of the parent plant.
Dog-strangling Vine seed pods
DSV is capable of forming dense colonies that out-compete and overwhelm native ground vegetation in a wide variety of habitats. Once established, it can quickly spread due to its wind dispersed seeds and aggressive root system.
In addition, the similarity of DSV to native Milkweed species has had a negative effect on Monarch Butterfly populations. Eggs that are laid on DSV are unable to provide the food necessary for Monarch larval growth, as this food is only available on native Milkweed species2.
Early detection and removal of DSV is the best means of controlling it. The plant can be dug out of the ground, with careful attention given to ensuring the roots are removed in their entirety. After a year or more of growth, DSV becomes much harder to control because it will grow an extensive root system that is difficult to completely remove. Roots left in the ground will often resprout. Another control strategy that can be used is cutting the plant back multiple times a year. This limits its reproductive output, and stops it from seeding, however it will not entirely eliminate plants already present3. Chemical control is the most effective method to manage large Dog-strangling vine populations3.
*CVC is interested in any locations of Dog-strangling vine and is tracking the population within our watershed. If you think you have located Dog-strangling vine, please contact CVC via email and call the Ontario Federation for Anglers and Hunters Invasive Species Hotline at 1-800-563-7711 for outside of the watershed and add the sighting to the EDDMaps Ontario website.
https://youtu.be/porOMb_w3WE (Video created by Ontario’s Invading Species Awareness Program)
Links for Further Information:
Ontario Invasive Plant Council’s “Invasive Dog-strangling Vine (Vincetoxicum rossicum): Best Management Practices in Ontario”: https://www.ontarioinvasiveplants.ca/wp-content/uploads/2016/06/OIPC_BMP_DogStranglingVine.pdf
Ontario Invasive Plant Council’s “Dog-strangling Vine (Cynanchum rossicum) Best Management Practice Technical Document for Land Managers”: https://www.ontarioinvasiveplants.ca/wp-content/uploads/2017/05/OIPC_TechnicalBMP_DogStranglingVine_Apr282017_D6_WEB.pdf
Averill, K.M., DiTommaso, A., Mohler, C.L. and L.R. Milbrath. 2011. “Survival, Growth, and Fecundity of the Invasive Swallowworts (Vincetoxicum rossicum and V. nigrum) in New York State”. Invasive Plant Science and Management. 4(2) 198-206. Web. 14 August 2018. https://www.researchgate.net/Swallowworts_Vincetoxicum_rossicum_and_V_nigrum.pdf
Ontario’s Invasive Species Awareness Program. 2012. “Dog-Strangling Vine”. Ontario Federation of Anglers and Hunters. Web. 14 August 2018. http://www.invadingspecies.com/dog-strangling-vine/
Lawlor, F. 2006. “Fact Sheet: Pale Swallow-Wort.” Plant Conservation Alliance’a Alien Plant Working Group. Web. 14 August 2018. https://www.invasive.org/weedcd/pdfs/wgw/paleswallowwort.pdf