3 March 2008

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.


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.


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 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.


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

DSV Fact Sheets:

Essential DSV reading:

More info on control strategies 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.


steve s said...

Hi. You might not be aware that cup-plant and grey headed coneflower aren't native to the Toronto area. Also my last record search showed that Black swallow-wort hasn't been seen in Ontario in 50 years. Many museum specimens at the ROM were misidentified but have been corrected.
Steve S.

native plant girl said...

hi! :)

The more I know the less I know – but this one has me really confused. Please help me out?

1. Cup Plant Silphium perfoliatum and Grey-headed Coneflower are both native to southern Ontario. yes?

…and in here in Toronto, I’ve seen them in restorations at High Park and Todmorden Mills. I’ve also talked to a couple of restorationists who recommend them here – this is the first I’ve heard of them NOT being native here. but I’m open-minded: it’s not like I was here 600 years ago taking pics & notes.

2. Black swallow-wort (just when I think DSV has found every possible way to be a pain in the ass)
-if that's the fact, there's a lot of info pieces and folks who need to be corrected. :(

do you think this was a misidentification or not: Vincetoxicum nigrum / Cynanchum louiseae:
"Populations of C. louiseae are scattered in southern and eastern Ontario and in southern Quebec"
see Figure 7B, page 251.
-you’re too smart to confuse the black swallow-wort with Cynanchum Vincetoxicum (white flowering) which has infrequent occurrences but not naturalized here… but just excluding it for sure (for anyone else who might read this too).

Exasperated - BTW: i have no ego to bruise and I don't even pretend to have expertise. I simply want to get DSV (and accurate concern and control strategies) on more folks’ radar so we’ll all have a better chance at managing it. (oh, and to be trying to do something to get the pain-out-of-my-chest that I get whenever I think of or see DSV.)

steve s said...

Hi. Grey headed coneflower and cupplant are native to southwestern Ontario but not this far north. They have been used in some restoration projects (including a couple of mine, though I wouldn't do it again today) but don't really belong here. Cupplant is so aggressive that it's almost an invasive itself.

Always more important to be right than to try to justify your own mistakes.

Books and museum specimens have made the pale/black swallowwort mistake for decades. People had it mostly right over the past few years but now black is creeping back into the popular literature. I think black was in a wildflower book once but pale wasn't so people think it's the one in the book without checking.

There are listings for Cynanchum vincetoxicum in Ontario but they were long ago (in Niagara) and it hasn't been seen since. I saw all the specimens at the ROM herbarium a few years ago and many were id'd as black but were corrected later as pale.

Anything written from the US may or may not be accurate. I'm not aware of any new mapping that's been done recently, but had an inquiry yesterday from a student at Trent wanting to map its distribution.

native plant girl said...

cup-plant... shake my head, but... i have to laugh: i've loaded my neighbourhood with them! but i can go back and correct some of that.

reminds me: Jimm Robb mentioned "the seed zone maps are being redrawn ... but that's ok... I like Mary's plants."

so,who knows, maybe our TO cup-planting was just ahead of its time? ;)

steve s said...

It's not too bad. Better than exotics. Just think of it as a garden plant. Go with the existing zone maps for now.

guild-rez said...

Just found this DSV advise on your site.
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."
Cara Webster, City of Toronto advises against the disposal of DSV seed pods and roots with City garbage, yard waste or green bin collection. Cara said burning or keeping the seed & roots in black plastic bags until dry and dispose at a later time.
Please comment and I wish you a Happy New Year!
- Cheers Gisela

native plant girl said...

Hi Gisela! :)

truly sorry it's taken me few days here... i still don't have a definitive answer. but i'll tell you what's up:

what i think we need to see is a primary source document (data, research, a report) that tells us how anyone knows that our city's yard waste treatment facility kills DSV (or better yet, all invasive weed) seeds and reproductive parts. or, any information that allows folks like us to make an informed or assured decision.

and i haven't been able to find that yet.

it's a very good question btw! :) i've heard a lot of folks wonder about it or have an opinion on it, but, now that you've got me thinking hard about it, i've never seen a reference to supporting document.

An education isn't how much you have committed to memory, or even how much you know. It's being able to differentiate between what you do know and what you don't. –Anatole France

I'm trying to contact the City of Toronto's Solid Waste Management folks, but their customer service line, 416-338-2010, has been rendered to a busy signal for now (they're STILL sorting out the new garbage bins). I'll keep trying. if i don't get through today, I think I’ll look-up and contact a department staffer directly. I've also emailed Cara w/ this, and I'll forward her response once I have it.

The only thing I'm certain about is, again, that DSV seeds and reproductive parts (including flowering parts that can still turn into seeds should NOT go into back yard composters. because the composters don't get hot enough, or seeds live longer than the period that most folks keep their compost isolated. also, if folks have a open air compost pile, those seeds can blow or be carried by animals. And the same goes for any of the other invasive weeds I can think of that we deal with around here (so i'm really hoping that the Yard Waste collection stream is indeed a convincingly effective and safe option!).

If you or anyone else opts to dispose of DSV on-site / in their yard, the best DSV seed disposal info I've seen is on the Fletcher Wildlife Garden's DSV page. BTW: the "city" yard waste composting facility they mention is in Ottawa.


love what you're doing for DSV public awareness in your/our area. thanks for grappling with it.

Regardless, DSV isn’t going to be solved by you or I or anyone overnight. I'm at a point where I’m crossing my fingers for an appropriate bio-control / suite of bio-controls. otherwise, trying to stop seed blow in the areas i have my hand in. oh, yeah, and trying get basic awareness (ID and basic removal or control) out to folks in those same areas too. i'm thinking that the best approach is lots of public education and local action. and i mean do mean local action. not only at the watershed-level (local volunteer stewardship teams try to control some DSV in natural areas every year; the TRCA and the City's Parks and Rec Naturalization department too), but hyper-local like, in my neighbourhood and on my street. on that level i can still go for eradication of isolated occurrences. but, I found that our main mother-source of DSV seed blow here is coming from a railway a few streets over. (the railway is fenced in, and no trespassing there of course anyway, so i have to deal with those folks) and also there's a smaller source (all of a sudden) inside of an unstaffed commercial property's fenced & locked parking lot (have to find out who to contact). education in my neighborhood has been person by person (even last summer, DSV was new to some of our regular local city hort crew staff btw). And, I also try to offer what support I can (some volunteer time) for orgs and folks who are trying to to have an impact on policy and practise too. i'm thankful for the folks and orgs who are trying to do the same things but on a larger scale too.

we have to support each other, and take care of ourselves too.

if you’re a mortal like me, DSV can be devastating: i've lost a lot of what i love to it. and i know for a fact that it has the potential to drive folks around the bend too. :) so, i hope you're kind to yourself, and feel ok to take some breaks, step-way, ease-up when you feel overwhelmed by it and “live to fight another day”. as you obviously know, there’s also a lot of other very important, hopeful & nourishing work the good plants and critters still need a hand with too!

hugs & courage

native plant girl said...

Today I’m slowly getting referred up the ranks (i'm on my 3rd) at City Solid Waste w/ this question. still, these are folks who deal w/ a lot of aspects Solid Waste here, so each time, they say: “I’ve never even thought about that one!” and want to know about the kinds of folks who have to think about this & why. But they've been really kind.

Also Cara responded with a lead, some she knows who might have some answers. And ill give them try and tell you if it pans out.

cara wrote some other interesting things --- as cara does so well! :)

"They are supposed to use high heat but I always wonder about whether it really kills the seeds - there hasn't been a lot of research on this but a lot of people are asking. That is really why I somewhat discourage people from disposing of DSV - I think it's better to keep it on site where there is already a seed bank. There are some recommendations that I think would help -

1) only cut or dig DSV prior to pod development i.e. at time of flowering not when seed are already viable

2) if you do remove a small quantity in your yard then put it into a plastic bag and let it solarize prior to putting into the compost system - hopefully this extra drying/cooking will help kill the seeds. I think this is manageable for an average homeowner in Toronto - larger scale than that not really feasible at this time. ...I have always been concerned with community groups doing huge manual pulling/cutting of DSV and then putting the material into the city garbage [note: practises differ, and the community site i'm on now hasn't sent DSV to landfill for 5 years.- michou] which is then shipped to Michigan where they don't currently have a huge DSV issue if at all. I would rather see that we keep the material in Toronto where it is already established. ...I will try to add this to a list for future student research projects."

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