DOG-STRANGLING VINE
(Vincetoxicum rossicum, Vincetoxicum nigrum)

Name and Family

Dog-strangling vine (DSV), Vincetoxicum nigrum & Vincetoxicum rossicum, are members of the Apocynaceae or dogbane family. These plants are alternatively known as pale swallow-wort (V. rossicum) or black swallow-wort (V. nigrum).

History

Dog-stangling vine was introduced to North America from Europe sometime during the mid-late 1800s for use as an ornamental plant. The plant was first identified in Canada (Ontario) shortly after its initial identification in the United States. Today, the plant is found in Ontario, Quebec, New Brunswick, Nova Scotia, and many U.S. States. It was first reported on PEI in late 2024. The plant has been reported in British Columbia but is not currently known to grow there. The plant has been investigated as a potential source of latex for rubber production. The plant does not actually strangle dogs, but other members of the dogbane family have been used as dog poison historically. While it does not strangle dogs, it does “strangle” other plants that it climbs up.

Identification Guide

  • Leaves: Opposite arrangement. Small, round leaves near the base of the plant. Larger, rounded leaves with pointed tips are found near the middle of the stem. Leaves become narrower and more pointed towards the top of the stem. The leaves are predominantly oval-shaped. Leaves are darker and smaller than those of milkweed. Leaf margins are smooth and often wavy, and the surfaces are glossy (as seen in glossy buckthorn).
  • Stems: covered in fine hairs.
  • Flowers: Clusters of small, five-petaled flowers bloom in June or July. Flowers are pink or purple in V. nigrum, cream-coloured in V. rossicum. Flowers are found all over the plant, close to the stem.
  • Fruit: Long, chili-pepper-shaped seed pods are produced in pairs and are found in July and August. Seed pods (4-7cm long) change from green to tan with age and leak milky sap when damaged. Seeds are white and have feathery attachment that allows them to cling to animals and catch on the wind. In full sun, more seeds are produced, up to 2000 seeds per m^2. Seeds have a high rate of survival (they are multi-embryonic).
  • Growth habit: Vine. Climbs up to 2m high using other plants for support. Grows densely and will often form a complete monoculture.
  • Methods of spread: Perennial. Transplant of whole plants, seeds, or root pieces. Wind dispersal. Rhizomes can sprout and create new plants.
  • Shade tolerant, drought tolerant, and often grows in dense vegetation, on which it relies for support to grow taller.

Impacts

  • DSV acts as a false host for the monarch butterfly. When the monarch lays its eggs, it does so on milkweed plants. The new caterpillars require milkweed as a food source and will die without it. When adult monarchs mistakenly lay their eggs on DSV, the caterpillars are unable to complete their life cycle and die before they can become adults. Himalayan balsam, another invasive plant, has reportedly caused similar impacts. 
  • DSV will outcompete native vegetation, rapidly becoming the dominant plant where it grows and even forming complete monocultures. Where native vegetation is displaced, wildlife habitat can also be impacted through the loss of food and shelter. 
  • DSV impacts forests and forestry by competing for space with young trees, weighing them down, diverting nutrients, and taking up space in a forest environment. Mats of DSV can make forests difficult to access and add costs to forestry operations. 
  • DSV is poisonous to humans and other mammals. An infestation can make horse pastureland unusable. The poison it contains is a haemolytic glycoside, vincetoxin.
  • DSV can block access to natural areas, impeding recreational activities.
  • DSV can lower arthropod diversity. In DSV stands, a lower abundance of stem and ground-dwelling species is found. Gall-makers and miner insects are completely absent.
  • DSV presence may reduce the nesting capabilities of ground-nesting birds.
  • DSV presence can shelter nuisance rodents from predation, increasing their numbers, which could lead to public health and infrastructure issues.
  • DSV acts as a wild/alternative host of important crop pests and diseases, potentially leading to indirect agricultural impacts.
  • DSV can outcompete crops in a no-till farming system.
  • DSV spreads by wind and is thus likely to do well on PEI.

Reporting

  • DSV is only known to exist in scattered patches across the Island. Reports have been sourced from both King’s and Prince counties. Because of its limited distribution, the PEIISC has targeted the plant for complete eradication in the province. 
  • Report any suspected populations of DSV to the PEIISC immediately by email at peiinvasives@gmail.com. Include as much information as possible in your report, but at a minimum, include:
    • The location.
    • The date when you found it.
    • Your contact information.
    • Clear, detailed photos of all parts of the plant, its surroundings, and any other notable features.
  • PEIISC staff will respond to your report within one week.

Management

  • Management of DSV will likely be an involved, long-term project, so be prepared to revisit the management site year after year to manage new growth. Regrowth will occur from seeds accumulated in the soil, from left-behind roots regrowing, or from seeds blowing into the site from the surrounding area.
  • DSV poses a serious tripping hazard.
  • If DSV is growing in multiple patches, focus on the smaller, outer patches first. These are called “satellite patches”. These patches have the highest potential to spread outward, and will also be simpler to manage before they can become more well-established. 
  • Conduct a site survey before management starts. Considerations to be included in the survey include:
    • The size of the infestation.
    • Your available resources.
    • The amount of effort you are willing/able to expend. Often, multiple control methods are used simultaneously to intensify the effect.
    • Consider the local ecosystem and what other organisms or ecological processes may be affected by management. Choose an effective method of control that will cause the least general disturbance. Wildlife habitat nearby may be disturbed or affected by management either directly or indirectly.
      • If you notice things like nesting birds, salmon redds, or a den, consider whether it would be better to conduct management at a later date.
      • With large teams of people, trampling becomes a concern.
    • The presence of hazards. 
    • The presence of other invasive species that may move into the managed space after control of the primary species has been conducted. You don’t want to replace one issue with another one.
    • The presence of native plants that you may want to preserve. Preserving native plants will provide competition for any regrowth that may occur after initial invasive plant management. If possible, maintain beneficial native plant cover. 
    • Removal of vegetation can influence erosion, hydrology, sedimentation, and other aspects of an area, which may cause significant effects to the environment more broadly.
    • Bank areas are especially susceptible to the removal of vegetation and may become completely destabilized.
    • Most removal of vegetation within a wetland, watercourse, or within 15m of one without a permit is prohibited.
    • The presence of property and infrastructure that may be impacted by management.
    • Share survey results with all management participants to ensure safe and efficient work proceeds.
  • Digging
    • This method involves using shovels to remove the root ball of the plant.
    • Removing the root ball will ensure the plant cannot resprout, reducing the time it takes to eradicate.
    • Tamp the soil back into place to reduce the chance of stimulating germination of any seeds that may persist in the soil. 
    • The plant will probably regrow in the months and years to come from seeds built up below the soil surface. Continue management of any plants that regrow for at least three years or until the plant is no longer seen.
    • After a few years of treatment, eradication is likely.
    • This method should not be used in areas where soil disturbance needs to be limited, such as along a bank.
    • Time this treatment to occur before the plant produces seed. If the plant has produced seed, see the seed head removal section before conducting management. 
    • Best for smaller populations, as this method is quite labour-intensive.
  • Pulling
    • This method involves hand-pulling or using a weed wrench to uproot the plant.
    • Do your best not to break stems. This will leave the roots intact and lead to resprouting. Plants may resprout aggressively, which could worsen the issue. 
    • If you are having trouble with stem breakage, avoid this method. Switch to digging (above), clipping, or mowing (below).
    • After a few years of treatment, eradication is likely. Eradication may take longer when pulling than digging, as you are more likely to leave behind root fragments that can resprout. Because of this, it is recommended that you combine the two tactics where possible. Pulling alone can be used in areas where soil disturbance needs to be limited.
    • Time this treatment to occur before the plant produces seed. If the plant has produced seed, see the seed head removal section before conducting management. 
    • Tamp down soil into place to reduce the chance of stimulating germination of any seeds that may persist in the soil. 
    • The plant will probably regrow in the months and years to come from seeds built up below the soil surface. Continue management of any plants that regrow for at least three years or until the plant is no longer seen. 
    • Best for smaller populations, as this method is quite labour-intensive.
  • Clipping
    • If you do not have time to pull carefully, do not have a mower (or cannot access the site with a mower), or are worried about spreading the plant on your mower, clipping can be used.
    • This method may prove more useful than pulling if stems are breaking, but it will not eradicate the plant immediately. Repeated clipping at regular intervals over time may show results as the roots become depleted of their nutrients, with no foliage to replenish nutrients. At the least, clipping sets the plant back and can prevent seed production. 
    • Simply clip the vines close to the soil and dispose of them either in a dry area on site (if clipped before flowers and seeds have formed) or dispose of the plant material formally (especially if clipped after flowers or seeds have formed)
  • Mowing
    • Mowing DSV will not kill the plant, but can set it back and prevent seed spread.
    • Time mowing to occur just after the plants flower. This will ensure the bulk of the plant’s energy reserves are in its aboveground parts, and thus the roots will be at their weakest. When the plant regrows, it will not be as vigorous.
    • Do not mow DSV after the plant has gone to seed, as this will likely lead to seed spread. 
    • If you would like to keep DSV from climbing on nearby plants or impeding passage, you can mow regularly (every 2 weeks) all through the growing season.
    • Many years of consistent mowing may exhaust the plants over time, killing them, but other methods are recommended if swift eradication is the primary goal.
    • Before leaving the site, thoroughly remove any organic matter from the mower. This can prevent the spread of DSV to other places where the mower will be used. 
  • Cutting and covering
    • This method involves cutting down the population and covering the affected area with a tarp or sheet of other opaque material. 
    • This method works best in areas of full sun, as the area beneath the tarp will heat up, causing further damage to the plants. Areas where soil disturbance must be limited are also ideal choices for the use of this method. Areas of low sunlight can also see results, but it will probably take longer. 
    • As this method is non-selective, all plants under the tarp will be affected. Consider relocating any plants you want to save. This method is thus most applicable to monocultures (areas where the only plant is DSV).
    • Effective for both large and small populations.
    • The PEIISC recommends polyurethane (4-8mm thick) cut to size. Polyurethane creates a solid barrier without any breaks through which a plant could pass. 
    • If you are on a budget, visit any lumber yard and ask the manager if you can take some lumber wrap. This is a tarp within which lumber comes wrapped. Lumber yards are usually willing to provide it for free, as it’s just trash to them. 
    • The tarp should be installed in late spring/early summer. Allow the plant to grow up a bit, then cut it down and cover it. By letting the plant grow up, you are using up some of its energy reserves and weakening remaining roots. 
    • Cut material can be left on site to decompose if not in seed.
    • The tarp should be dark-coloured or opaque. Light colours will allow some light through, which will be beneficial for the plant. 
    • Tape any holes in the tarp with UV-resistant duct tape, ideally on both sides of the tarp. Remove any sharp stems or other objects that may pierce the tarp from the area.
    • Once the tarp is confirmed to be solid, install it over the affected area. 
    • If using multiple tarps to cover the area, overlap breaks by at least one foot and then tape the tarps together. 
    • Once the tarp is covering the area, secure it. If possible, bury the tarp’s edges on all sides to prevent billowing in the wind. Sealing the area may also create an oxygen-poor environment, stimulating microbial activity and potentially causing decay.
    • Additionally, the tarp can be covered with 8” of soil and then replanted with native plants.
      • Select plants that are drought-tolerant and can survive in the shallow soil layer. 
      • Alternatively, use a biodegradable covering material such as geotextile or jute, which will degrade over time to help keep plants from desiccating after an extended period in shallow soil.
    • Over time, the tarp will kill the plants below. The time this process takes to become effective can vary based on site conditions, materials used, etc. Every month, check beneath the tarp to see if anything is alive. If you see live plants, recover the area. If the plants are dead, you are probably safe to remove the tarp. 
    • Monitor the area thereafter to see if any DSV regrows. If it regrows, consider replacing the tarp or doing digging or pulling at the site. 
  • Seed head removal
    • After DSV has produced seed, management by the above methods will likely lead to the spread if seed pods are not carefully collected. 
    • At this stage, before managing DSV, carefully remove and collect all seed pods for formal disposal. 
    • Use a clear plastic bag. While the plant is still intact, move the seed pods into the bag, being careful not to dislodge them. Cinch the bag opening along the stem above where the seed pods are growing. Clip the stem above the bag. This will ensure that the seeds all fall in the bag. 
    • Dispose of the seeds formally. See below for formal disposal requirements.
    • You should return to the site a few weeks later to check if new seeds have been produced, and address these seeds as above.
  • Chemical control
    • The PEIISC does not provide advice on chemical control measures at this time.  
    • If using chemical controls, it is imperative that all local legislation and the manufacturer’s label be followed during the purchase, storage, transport, preparation, and application of pesticide products. 
    • Studies have shown that digging can be more effective than herbicide use, and is likely much cheaper too. 
  • Biological control
    • Biological controls are considered to be a long-term solution designed to reduce the impacts of an established invasive species. Biological controls will not eradicate the target, but merely mitigate its impacts.
    • As the PEIISC does not consider the plant to be well-established on PEI, we are targeting the plant for eradication. Thus, biological controls are not compatible with our control program, and we will not be undertaking any such releases at the time. 
    • Biological control release is a highly regulated process and should only be undertaken by professionals with the necessary regulatory approval. Do not attempt a biological control release on your own. 
    • For more information on biological control of DSV, check out this article: https://ofnc.ca/fletcher-wildlife-garden/biocontrol-of-dog-strangling-vine 
  • Not recommended
    • Grazing
    • Trampling

Disposal & site exit

  • It is imperative that all equipment be cleaned thoroughly and that all plant parts are removed from boots and clothing before leaving the area. 
  • All plant parts, especially roots and seed heads, must be collected, bagged, and properly disposed of. 
  • If the plant is not in flower or seed, you may be able to leave plant material on site on an impervious surface (like tarmac or a tarp). If the plant has produced flowers or seeds, the plant must be formally disposed of as below. Even if the plant is just in flower, flowers can still go to seed after the plant has been uprooted or clipped under the right conditions, and cause spread.
  • Each time you manage the site, collect, bag, mark, and dispose of all plant parts properly.
    • Bag the plant material in clear plastic bags.
    • Mark the bags boldly with a permanent marker. Write “INVASIVE PLANTS” or “DOG-STRANGLING VINE” on the bags. 
    • If you have a place away from foot and wildlife traffic, you can dry out the material, making it much easier to move.
      • Leave the bags open and in the sun for a week to dry. 
      • Only do this if you can guarantee that the plant will not be spread from where it is drying
    • Double bag the bags to prevent accidental dispersal later on and protect waste handlers from the plant’s toxic properties.
    • Tie the bags tightly and place them in your usual residential waste collection (THE BLACK BIN)
      • Never place invasive plants into the compost. This may allow them to become established once they reach the heap. 
      • Up to two additional bags of material can be labelled and placed beside the bin for pickup in case your bin is full already.
  • As this plant is toxic, it would be well advised to double bag the plants to prevent any accidental dispersal during transit and help keep any waste handlers safe. 
  • Loads larger than what would fit in your residential waste collection bin but smaller than a half-ton truck bed full can be brought to any Waste Watch disposal depot during business hours.
    • Bag and label the material as above. 
    • Load the material, ensuring it will not blow away and disperse during transport. 
    • When you arrive at the depot, inform the gatekeeper at the scales that you have invasive species. You will be directed to a specific area where you can safely unload the material. 
    • Before leaving, pay the associated fee at the scales. A full truckload will usually run you 15-25$ depending on the material’s weight.
  • For loads larger than what would fit into a ½ ton truck, contact the PEIISC for specific disposal instructions. A special waste permit may be required.
  • Before leaving the site, ensure that there is no stray organic material (seeds, stems, mud, etc.) on your person or equipment. Movement of organic material can lead to the spread of invasive species as well as other pests and diseases. 
  • Sometimes, bagged material can be left on-site with the bags open to dry out. This can make loads

Remediation and restoration

  • If tarping, consider adding soil amendments to the area to restore mycorrhizal fungi and other beneficial soil organisms that may have been killed by high heat. 
  • Do not leave the area bare, as this may invite a new invasive species to move in and grow. 
  • Once the area has been cleared of invasive plants, consider what you want the area to look like afterward. What functions do you want it to perform? Select native or non-invasive plants to replant in the area. If you are struggling to decide what to plant, look around the area. Do you see any other native plants growing there? These are likely good choices to replant in the affected area. Are you still having trouble? Reach out to the PEIISC for suggestions.
  • Take time to consider and select plants that fit your vision for the site. Do you want plants that will grow quickly? Plants that have deep roots? Those that supply nutrition and shelter to wildlife? 
  • Soil testing may help inform restoration activities.

References

Image gallery

Gallery Photo Credits: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org