Dog-Strangling Vine

"We stand to lose our natural ecosystem, all our native plants, everywhere in the Great Lakes Basin and southern Ontario.” - Ontario Ministry of Natural Resources Ecologist Waysel Bakowsky, when asked about the threat of DSV.

Dog-Strangling Vine is a highly invasive perennial vine that dominates and destroys ecosystems.If you see this plant on your property, or your local park or community garden, the alley where you walk your dog, the parking lot at work, the playground at your kid's day care, your mother-in-laws' garden, or your neighbour's yard (with their permission of course) please remove it. ...before it looks like this:or worse, this:

photo by Stephen J. Darbyshire

"DSV" is some times understood to be two similar species (Pale Swallow-wort Cynanchum rossicum or Vincetoxicum rossicum which prefers sun, and Black Swallow-wort Cynanchum louiseae or Vincetoxicum nigrum) but, for most practical purposes it's generally referred to, and treated as, simply DSV.

DSV is invading, dominating and destroying natural areas, habitats and ecosystem functions in and near our area: oak savannah, forests, woodlands, tallgrass prairies, meadows, even alvars. DSV directly threatens to displace all of our native plants, in all of our natural areas, except wetlands (although it does grow along riparian river and stream edges). It spreads by prolific wind-dispersed seeds similar to our native milkweeds. Seeds are poly-embryonic (one seed can produce several viable embryos / plants). Plants can self-pollinate in a single day. Research has found decline in the populations and diversity of insects in old fields dominated by DSV. DSV displaces native Milkweed species, impacting pollinators who depend on them. Also, in experiments, when given the choice of both DSV and Milkweed, Monarch butterflies have been observed laying up to 1/4 of their eggs on DSV, resulting in death of those larvae. DSV is salt-tolerant and can handle a range of substrates with variable pH's from limestone to granite, and is found in gravel, clay and sandy soils. Currently there are no biological controls to keep DSV in check.

REMOVE:

How? Dig out the entire root of the plant (pulling is ineffective: roots will persist and form several plants). Its easier if you use the right tools (weed rockers don't get out all the brittle roots, and planting trowels are often dull and clumsy when used as weeding tools). In hard compacted soils, try using a sharper-edged trowel or spade. Also a "Weed Wrench" is recommended (Mary Gartshore, Pterophylla Nurseries). If you do dig out the roots (good for you!), avoid any unnecessary soil disturbance (it day lights existing seed bank in the soil and also provides a place for new invasive seeds to enter) and backfill the hole to prevent further invasion. At this point you can also either replant with the area with desired species (of course I'm recommending natives) and/or cover the area with mulch.

In infestations too large to dig out, control further spreading by cutting the plants. This will help to prevent seed pods from maturing. You will likely have to cut at least twice during the season (every year for the 1st few years), as plants continue to produce seeds from May to November. (Note: Fletcher Wildlife Garden has had some success with a single cut per year when timed around June 26.) Common tools used for cutting: garden shears (but they can be hard on the back), weed whippers and mowers. However, Fletcher Wildlife Garden has found scythes to be easier, efficient (requiring less volunteers and time) and more manouverable when trying to cut around desired plant species among the DSV. Scythes are available at Lee Valley for $112.

Larger patches can also be controlled by covering the area with tarps or landscape barrier fabrics (secured by landscape fabric stakes / pegs or coat hangers) or a thick layer of newspaper for several months, followed by the removing remaining persisting plants. Another control option is Glyphosate (aka Round-Up). Glyphosate is not a one-shot deal: Cara Webster (City of Toronto Urban Forestry) recommends 2 glyphosate applications each year for the 1st 2 years. Please see this earlier post for more information about glyphosate and DSV.

DISPOSE:

After removing or cutting DSV, DO NOT dispose of roots or seeds in your garden composter, or in a open air pile. Reproductive parts of DSV and other weeds can go into regular city yard waste collection.

REPLANT:

Replant weeded area with local native plants (e.g. for no cost: use nearby in-season seeds such as common milkweed, cup plant, grey-headed coneflower) or transplant other ethically acquired native plants (the $5 for SER-O's 2007-2008 Native Plant Resource Guide is money well spent!). Start with common native plants that are most likely to survive and become establish (one possible strategy might be to start with the more aggressive colonizing natives.) DSV appears to be more aggressive and capable of producing more seeds in sunny areas, however, it can also invade thicket (e.g sumacs, hawthorns and even dense cedars - Patricia Mohr) and shady areas (growing up to 9 feet, covering and out-competing shrubs and tree seedlings). However, it's most often it's along the forest edges and openings than dense shade areas. DSV "doesn't do well in areas of continuous dense forest" (Forester Jim Robb from Friends of the Rouge Watershed). For existing or new shade areas, plant with all successional forest layers (ground cover ->herbaceous layer -> shrub ->vine ->trees. For trees, Jim Robb recommends including fast growing early successional poplars and aspen as well as pine, alongside broad leaf hardwoods).

Along with planting in successional layers and using common locally adapted native plants appropriate for your site's conditions, two other defensive planting strategies are: planting in high density (more plants /sq M) and, planting in seasonal guilds -- the idea being continuous coverage through the warm seasons, for example: early spring = early woodland ephemerals like ginger, bloodroot, may apple; summer = woodland sunflower; autumn = zig-zag goldenrod and big-leaved aster.

Some plants seem to withstand DSV invasion better than others, possibly as a result of their allelopathic properties, including Zig-zag goldenrod (Todmorden Mills Wildflower Preserve, Sept. 2006 Newsletter), tall goldenrod (Steve Smith, Urban Forest Associates Inc.), some juglone spp. (Jim Robb), and also flowering raspberry (Fletcher Wildlife Garden), Colorado Blue Spruce (non-native but not invasive)(Gavin Miller). After planting, add a thick layer of mulch on bare ground around desired species.

To prevent DSV and other invasions: keep your healthy areas healthy (use mulch / leaf litter, do not disturb soils unnecessarily, grow plants adapted to your site conditions and region, do not use synthetic fertilizers or salts, catch and control any invasive early on), also plant and/or mulch nearby bare ground patches and disturbed areas and understorey vacancies, before they fill with invasives.

RETURN:

Continue to cut and control nearby DSV, monitor, weed, mulch and replant the area.

DSV Fact Sheets:

• Controlling Invasive Plants - City of Toronto
• Pale Swallow-wort - Fletcher Wildlife Garden
• Black Swallow-wort – Midwest Invasive Plant Network
• Black Swallow-wort and Pale Swallow-wort - Plant Conservation Alliance’s Alien Plant Working Group (PCA APWG)

Essential DSV reading:

• Gavin Miller, TRCA. Dog-strangling vine - Cynanchum rossicum (Kleopow) Borhidi: a review of distribution, ecology, and control of this invasive exotic plant. Fall 2007.
  
• Fletcher Wildlife Garden, Ottawa Ontario: Swallow-wort research (be sure to also read the “Sunday Volunteer” reports from 2006 and 2007)
• Di Tommaso, Antonio, Frances Lawlor and Stephen J. Darbyshire. 2005. The biology of invasive alien plants in Canada. 2. Cynanchum rossicum (Kleopow) Borhidi [= Vincetoxicum rossicum (Kleopow) Barbar.] and Cynanchum louiseae (L.) Kartesz & Gandhi [= Vincetoxivum nigrum (L.) Moench]. Canadian Journal of Plant Science, 85(1): 243-263.
• The Nature Conservancy’s Global Invasive Species Team (TNC Weeds) "Element Stewardship Abstracts" (or ESAs), with photographs: Pale swallow-wort, Black swallow-wort
• Cara Webster, City of Toronto Urban Forestry Restoration Challenges: The Ongoing Battle with Dog-strangling Vine Control at High Park

More info on control strategies and tools:

• T.C. Fuller & G. Douglas Barbe. “The Bradley method of Eliminating Exotic Plants from Natural Reserves", in CalEPPC News, Vol. 5, No.4, Fall 1997
• Thonas D. Brock. “The Bradley Method for Control of Invasive Plants”, The Newsletter of the Invasive Plants Association of Wisconsin, Issue 3 October 2002
  
• & thank you to folks at Todmorden Mills for directing me to those Bradley articles
• Weed Control Methods Handbook: Tools and Techniques for Use in Natural Areas Wildland Invasive Species Team – The Nature Conservancy. Includes manual methods and tools.

Get involved locally:

• volunteer on a stewardship site near you: GTA Stewardship and “Green Groups" listed by watershed
• take care of the lands (public or private) where you live
• take pictures of DSV and donate them to your local stewardship group, and use them yourself (on your own website, blog, newsletters, email lists, community garden agendas, meetings and workshops) alongside more information about DSV and what you can do about it.