The good folks of Trinity Anglican Church, in Marysville, Wolfe Island, first introduced me to Dog-strangling Vine (DSV), which is also called Swallow-wort, especially in the U.S. Concerned for church grounds as well as her village, Jean Cruickshank organized a number of us to pull the aggressively invasive vines which were threatening the church’s glorious lilacs. In 2017 alone, we collected 40 garbage bags of DSV! Unfortunately, a follow-up survey in 2018 showed that, in spite of parishioners’ efforts, Dog-strangling Vine had already staked its claim in Marysville.
Alerted by Jean and Master Gardener, Astrid Muschalla, the Township of Frontenac Islands helped with disposal of the material collected by Jean and her volunteers, and scheduled herbicide applications on rural roadsides of Howe and Wolfe Islands, one of its shore properties (on Wolfe Island), and Baseline Recreational Trail (on Howe Island), beginning in 2018.
The two species of invasive Dog-strangling Vine (Pale and Black Swallow-worts) are perennials in the milkweed family, which are spreading rapidly and causing damage to ecosystems, most recently in our area. The two species are very similar in appearance, ecological effects, and control implications. The vines are perhaps most noticeable for their glossy green leaves, proliferation, twining habit, and distinctive seed pods. In addition to plumed seeds, Dog-strangling Vines spread via underground rhizomes. Once established, they can present an impenetrable tangle to humans, livestock, and wildlife.
Swallow-worts (DSV) were introduced in northeastern North America in the mid-to late 1800s, escaped from cultivated gardens or experimental plantations, and now have patchy distributions in North America, with populations most concentrated in the northeastern United States and eastern Canada, according to Katharine Stone in her detailed 2009 review for the US Dept. of Agriculture. (Descriptions of DSV taxonomy and preferred habitats vary, but Stone’s (2009) comprehensive review makes hers a particularly good reference.)
According to the St. Lawrence-Eastern Lake Ontario Partnership for Regional Invasive Species Management of New York, Dog-strangling Vines:
• aggressively chokes-out desirable species. They are problematic in Christmas tree plantations, perennial crop fields, pastures, roadsides, disturbed areas, and natural areas;
• chemically suppress the establishment of other species and interfere with forest regeneration;
• are toxic to livestock and deer, which, avoiding the Vine, may over-browse preferred plants. Monarch Butterflies sometimes deposit their eggs on Dog-strangling Vine, rather than the milkweed that their caterpillars need to survive.
Regulatory Status in New York and Ontario
In New York, Black and Pale Swallow-worts (the two species of invasive DSV) are prohibited species, which cannot be knowingly possessed with the intent to sell, import, purchase, transport or introduce. In addition, no person shall sell, import, purchase, transport, introduce or propagate prohibited invasive species.
Dog-strangling Vine is classified as a noxious weed under Ontario’s Weed Control Act, which means that landowners whose property contains DSV and seeds that negatively affect agricultural and horticulture lands are responsible for weed control and associated costs. To prevent further spread and introduction, Ontario regulates possession, release, and disposal of DSV, a restricted species under its Invasive Species Act, which particularly emphasizes protection of provincial parks and conservation reserves.
Range and Site Susceptibility
Both Black and Pale Swallow-wort infestatiions are reported in New York (Cornell Cooperative Extension), and we believe both species are colonizing Wolfe Island. In addition to Wolfe Island, DSV has been reported on Howe and Simcoe Islands via EDDMapS. DSV have also been reported along Ontario’s north shore of the St. Lawrence River, according to Franklin Dickinson (University of Toronto). In his 2013 presentation, only sites with extreme cold, very fine soil texture (silt, clay), and/or very fertile soils were resistant to invasion by DSV. Least susceptible were planted communities of White Spruce, Jack Pine, Beech, and Aspen, but Stone (2009) found reports of DSV even there. Here on Wolfe Island, we see DSV in the thin soils covering our sedimentary bedrock (limestone alvars), and Dickinson reported that metasedimentary bedrock (i.e., granite, gneiss) were not immune to DSV invasion.
Except perhaps on the smallest island, it is unlikely that DSV can be eradicated. Our hope here on Wolfe Island is that we can protect our beautiful Big Sandy Bay, a provincial Area of Natural and Scientific Interest. We hope, too, that Islanders, once alerted, will monitor their properties, and consider early action to control the invader, individually and in cooperation with neighbours.
When removing an invasive plant from your yard, do not dump it in your compost or fire-pit. All plant materials should be placed in thick black plastic bags. Seal the bags tightly and leave them in direct sunlight for about a week. Allow it to dry out thoroughly before disposing.
Hayley Anderson’s Best Management Practices (reference below) provides a comprehensive overview of control measures for Dog-strangling Vine. In addition to the application of herbicides, cutting, pulling, mowing, and tarping is recommended, depending on the situation. Biological controls are being sought on both sides of the border, but none yet have proven safe and effective. To avoid spreading DSV further, we are cautioned against disturbing the plants once seeds are released, beginning in mid-summer. Care should be used in disposing of plant material, and follow-up monitoring is crucial to detect and remove DSV that may survive or be re-introduced after initial control efforts. Cooperation with neighbouring landowners and managers is recommended: educate and help one another, recognizing that in some situations, property owners have a legal responsibility to control the noxious weed. And, most importantly, as the professional botanist warns in an Ontario Nature video, Don’t ignore it. Those who catch Dog-strangling Vine early will have a much lighter task!
Margaret Dochoda is a seasonal resident living on Wolfe Island, ON. A retired fishery biologist on the Great Lakes, we look forward to receiving Margaret’s notices on her Yahoo Wolfe Island Forum discussion group. Her timely notices provide important information to Wolfe Island residents as well as for those of us living on islands downriver.
Comment by: Marg Dochoda Left at: 9:39 AM Friday, September 21, 2018
Naomi Cappuccino, Carleton University: Hypena opulenta, the biological control agent (moth) released to combat dog-strangling vine, has successfully established at the Ottawa release site. Caterpillars have been spotted during the summers of 2015, 2016 and 2017 and adults were caught at a blacklight trap in 2016. In 2017, caterpillars were observed in the Dominion Arboretum, 0.6 km from the release site. We suspect that some individuals may have gone even farther, but the numbers are still low overall, making it difficult for us to detect individuals. That's where we need your help! Please be on the lookout for the caterpillars, and let us know of any you see, by using the form on the page "Report Hypena opulenta sightings": https://dogstranglingvine.weebly.com/report-hypena-opulenta-sightings.html