by John Routh, Task Force Vice-Chair
photos courtesy of John Wilson
Click on images for larger versions
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| Ripe pods on the Pale Swallowwort or Dog-strangling Vine. |
Gardens are often beset with weedy plants that are not planted by the gardener. The seeds of many plants come into our manicured gardens and lawns on their own blown in by the wind, dropped by birds or stuck to our clothing or pets. Most of these plants are little more than a nuisance but occasionally there is one that can become a serious problem. One such plant is called Pale Swallowwort or Dog-strangling Vine (Cynanchum rossicum).
Dog-strangling Vine (DSV for short) is a perennial plant in the Milkweed family that grows between 30-250 cm in height. Its smooth-edged, dark green leaves grow opposite each other and the petioles (leaf stalks) hug the plant stem in a characteristic U-shaped pattern. The flowers which appear in June are small pale purple flowers with five petals. When it grows to about 50 cm in height, the tips start to twine around taller vegetation like trees and shrubs. When there is nothing else available it will twine around other DSV plants.
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| Dog-strangling Vine climbing |
Each DSV produces many seed pods which first appear as slender green pods about 3-4 cm long. In late August, the seed pods dry out and break open releasing hundreds of seeds. Each seed has a feathery attachment that allows it to float in the wind, much like dandelion seeds. A good wind can carry these seeds hundreds of metres away from the mother plant.
Dog-strangling Vine is an odd sounding name but is, in fact, harmless to dogs. It gets its name from the Latin species name. Cynancho is the Greek word for dog. DSV originally came from parts of southern Russia. It was first identified in Canada in 1885 but it has only become a problem since the 1970s.
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A mature patch
of DSV |
| DSV going to seed in late August. |
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It is now a serious invader of meadows and forests in southern Ontario. It grows in a variety of habitats including meadows and forests and tolerates a variety of soil and moisture conditions. Once it becomes established, it forms dense mats of growth where nothing else grows but DSV. Not only does it crowd out our native vegetation it also has had an impact on some of our cherished fauna. The Monarch Butterfly lays its eggs on plants in the milkweed family such as Common Milkweed, Swamp Milkweed and Butterfly Milkweed. It will also lay eggs on DSV but when the Monarch caterpillar hatches it can't eat the leaves of DSV and usually starves to death.
Once it establishes itself it is very hard to get rid of. The roots are short fleshy fibres that can become thick mats of growth that are well anchored in the soil. If you try to pull the plant by the stem it will likely break off at the base which only causes the plant to produce multiple stems. So how do you get rid of DSV? The recommended method is to dig it up. Use a shovel or spade and dig around the plant. When you have loosened the soil, carefully grasp the plant at the base and pull it from the soil. Shake the soil from the root mass and discard the plant. Make sure that you remove all the root mass because the plant can resprout. You can dispose the plant in your yard waste bag or put it in your compost bin. If there are any seed pods attached cut these off and place them in the garbage or the green bin.
Helpful links
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| Dog-strangling Vine is threatening to overtake our gardens. |
