Black Swallow-wort is a perennial vine from Europe that emerges in June. It has somewhat glossy, opposite leaves (i.e. the leaves are in pairs exactly opposite to each other along the vine stem). It has small purple flowers (starting in June, with new flowers over the rest of the summer), and then develops long seed pods that look like pea pods hanging down. The pods dry and burst in late summer and seeds are dispersed on white fluffy fibers by the wind.
BSW is our newest invader and a formidable problem. It clambers up fences, or through shrubs, and if those are not available it simply twines upon itself. It prolifically grows and seeds in sun or shade. It is also a threat to Monarch butterflies: because it is in the milkweed family, they may lay their eggs on it, but because it is not the right milkweed, the Monarch larvae find it inedible and they do not survive.
The spaghetti-like root system spreads with runners, and though individual plants can be dug up and a small infestation can be eradicated, once a larger infestation has taken hold of an area it is very difficult to dig.
Dig up individual plants using a garden knife or digging tool (a “japanese garden knife” is excellent for this). Dig a couple inches away from the stem down a few inches and try to loosen and pull out the spaghetti like roots.
If pods are on the vine, the pods or the entire plant must be disposed of as trash, not with yard waste, to prevent dispersal of seeds.
If it is not possible/feasible to dig up the plants, at least remove/pull off all the seed pods in mid summer before the pods dry and burst (put the seed pods in trash, NOT yard waste). You can also pull and break the stem at the base, but still pull off the pods. The plants will grow again next year, but at least removing the pods prevents innumerable more seeds from being dispersed in the wind.
Links and Resources
For more information on how to identify and control Black Swallow-wort, please refer to the resources below:
- Black Swallow-wort flyer for our flyer
- Mass Audubon for identification
- Michigan Department of Natural Resources for identification and control