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Dog Strangling Vine

Gary Westlake

Twice now we have come across a harmless looking vine in our garden. Lucky for us, we realized this was the infamous Swallow-Wort (Vincetoxicum) or Dog Strangling Vine and dug it out. Normally with a name like this, I would try to crack a joke but I am sad to say this vine is no joke. The few plants showing up in Peterborough are the vanguard of an army of garden and property destroyers that is not far behind.

Here is how it might happen to you. One year, one or two plants will find their way by seed to your property. They won’t look like much – just another weed. The next year each of these will spread to a small patch and there will be several other single plants around. Over the next few years, these patches will grow together choking out everything else. Later in the season, there will be a cloud of seeds spreading the infestation further. They can climb 8 to 10 feet high, forming dense mats that cover shrubs, small trees, and everything else. By this time you will be overwhelmed and everything you do (even if you could use chemicals) will be ineffective to stop the spread.

Dog Strangling vine, like Purple Loosestrife and most other invasive plants are alien to North America where it has no known natural controls. Dog Strangling Vine was brought in for its fluffy seeds as possible filler for life jackets during the war. It grows just about everywhere – in open pastures, in the woods, beside streams. The perennial vines shade and suppress all native plants and where they are established, form large areas where they are the only plants that can grow.

The vine is similar enough to the common milkweed that monarch butterflies will lay their eggs on it. Given a choice between the two plants, the butterflies will lay approximately 25% of their eggs on the Dog Strangling Vine. All of the resulting larvae die. This cannot be good for one of our favourite butterflies. Because of its destruction of natural habitat, it also affects the lives of native birds and wildlife.

In Ontario for the moment, populations of the vine are spotty. One of the areas where there is a serious problem, is the Millbrook and Cavan. I have heard from a person who works in gardens in the area that every garden she works in has the vine. She also said that the Fleetwood Creek Conservation Area has large patches of it. Because it has parachute-lifted seeds like milkweed, it can hop great distances to establish new areas. The dense roots (rhizomes) also help it to spread. Cutting the rhizomes has been shown to result in two new plants from each severed end.

Here is how you can identify it. Dog Strangling Vine is a twining vine, which means it twists around the things it climbs and does not have tendrils like a grapevine or suckers like a Virginia Creeper. It has pairs of pointed oval leaves about 3 to 4 inches long on opposite sides of the stem. There are small dark red or purple coloured flowers with five stubby petals. If you let it go to seed, it has pods reminiscent of milkweed but thinner containing the fluffy parachutes.

Control is most effective if you catch it early when it is just one or two plants. Dig them out (do not pull), making sure that you get as much of the root as possible especially the crown (the place where stem meets roots). Whatever you do, do not let them go to seed. If you could use chemicals in Peterborough, I am not sure it would help. It might suppress the Dog Strangling Vine, but it would probably suppress everything else more giving the Dog Strangling Vine a competitive advantage. Repeated mowing does not seem to be effective either but some success has been found with mowing and then covering with mulch.

I know this all sounds depressing, so I have looked for any reason to be hopeful. I have seen many times that nature finds a way to work things out so in the long run there probably will be a new balance reached. In the short term, it looks fairly bleak for areas of infestation. People are working on natural controls – trying to get some insect or disease to control Dog Strangling Vine. In Europe, this plant is not considered invasive because it has natural controls there. Maybe we will find a magic bullet, but until then be vigilant!