aka European or Black Swallow-wort
Vincetoxicum nigrum (L.)
Text: Candace Dressler
Diagram: Publication 505, Ontario Weeds, OMAFRA
What is Dog Strangling Vine?
Dog-strangling vine, Vincetoxicum nigrum (L.) Moench, aka: cynanque noir, Black swallow-wort, Cynanchum nigrum (L.)
A member of the Milkweed Family (Asclepiadaceae), it is thought to have been imported from Eurasia to North America in the late 19th century. It is a Noxious Weed as listed under the Ontario Weed Control Act, R.S.O. 1990, Chapter W.5. Dog strangling vine is a rapidly growing single stemmed vine with opposite oval leaves. It gets pretty little purple-brown star shaped flowers and then distinctive 4 – 6 cm long thin seed pods that split in late August to spread up to 30 000 seeds per square meter. It spreads by seed and by rhizome. It grows in a wide range of soil and light conditions, preferring to start at the edge of a hedge or forest. It smothers other plants out. It changes the soil around it so it is uninhabitable for native plants.
Photo: Barbara Long – MG
Dog Strangling vine can produce up to 30 000 seeds per square meter.
Photo: Barbara Long – MG
Dog Strangling vine invading a nearby woodland.
Why is in a noxious weed?
And why do we want to get rid of it?
It will strangle and smother off the native and cultivated species in your garden within a couple of years if left unchecked. It will reach 2 meters in height wrapping itself around trees and anything else it can find. Dog Strangling vine threatens the Monarch Butterfly. The butterflies mistake it for milkweed and lay their eggs on them, but the larvae cannot feed off the dog strangling vine and they die. The Ontario Weed control act states “Every person in possession of land shall destroy all noxious weeds on it. R.S.O. 1990, c. W.5, s. 3.” So now we know it needs to go how do we go about it?
Removal of Dog Strangling Vine
On large plants do not pull out, you will get a better response to cutting it off than pulling it. Pulling it causes the root to splinter and results in more plants: Each of the root threads will sprout a new vine and where you had one vine you will now have four.
Remove them to stop the spread by rhizome
• Physically remove the plant by digging it out, you need to get all of the crown of the root. Use a Japanese garden knife to dig out the young seedlings.
• Till the soil and then sift it to get all the pieces of crown root.
After removal a good thick layer of mulch will help stop the germination of seeds.
Control them to stop the spread by seed.
This will keep your invasion from spreading to your neighbours.
• Remove the flowers and seed pods: Cutting the plant off as close to the ground as possible.
• You may have to do it a couple of times per year.
• If the seed pods are starting to mature dispose of the plant material
in a black garbage bag, leave it in the sun for a couple of weeks before putting it in your regular waste, do not compost.
Volunteers working at removing Dog Strangling vine in an infested area.
Photos: Barbara Long – MG
Dog Strangling vine root crown.
This will sterilize the soil and kill any seeds left behind.
1. Cut the plants off as close to the ground as possible
2. Cover area with 2 to 4 mil clear plastic sheeting, anchoring the edges.
3. Leave for 6 – 8 weeks.
This method works best in the summer with lots of sunshine
You can find more detailed tutorials online.
According to The Landowner’s Guide To Controlling Invasive Woodland Plants the only herbicides recommended for dog strangling vine contain imazapyr.
OMAFRA’s Publication 75, Guide to Weed Control lists ARSENAL, glyphosate and TRUVIST as effective.
The Fletcher Wildlife Garden says glyphosate has variable results and may have to be reapplied over several years.
n.b. Imazapyr and glyphosate are listed as a class 9 herbicides, banned for use in Ontario unless the use is excepted. Exception may be given for invasive plant control, but you will need to have a licensed pesticide operator apply it