Field Notes: Dog Strangling Vine (aka Pale Swallow Wort, Cynanchum rossicum)

Here’s another invasive to look out for. I promise I’ll add some new natives soon, but with invasives it always seems more time sensitive. For example, now is the best time to take a chunk out of the Dog Strangling Vine population of Ottawa since most individuals haven’t yet produced their seed pods.

It is thought that this particular invasive made its way from Europe to Canada as a stuffing for lifejackets in the 1930s (Evergreen Canada Database). When it gets established somewhere it spreads both by seeds and by rhizomes, forming dense stands that literally smother out every other living plant. To see how devastating this weed can be once it has taken root check out some of the Fletcher Wildlife Garden’s old field site.

It doesn’t seem to have become a huge problem in Ottawa yet, outside of the Fletcher Gardens, but I have found a couple of patches in my backyard and seen it along a hedgerow in Westboro and along the bike path in Vincent Massey Park. So I would advise checking your own yard for black swallow wort and getting it before it becomes unmanageable. Dog strangling vine is related to milkweed and there is some troubling evidence that monarch butterflies can’t tell it apart from its cousin. Mistaking it for milkweed, they lay their eggs on it. However, the two plants are different enough that monarch larvae starve to death upon hatching because they cannot eat dog strangling vine.

For more info on identifying and controlling dog strangling vine (Cynanchum rossicum), check out Fletcher Wildlife Garden’s incredibly informative pages on renaturalizing gardens and controlling invasives in Ottawa.