Update 10/25/04:
Below are some pictures I took of swallowwort today, in case anyone is trying to make a fall ID.
—JM
Below are some pictures I took of swallowwort today, in case anyone is trying to make a fall ID.
—JM
Click here for a list of several links to more information, compiled by Michael Parker.
Thank you for your interest.
—Jane Milliman.
Black swallowwort, Cynanchum nigrum, and pale swallowwort, Cynanchum rossicum, are large (3 to 6 feet in reach) perennials, vining in habit, that are at home, in sun or shade, in almost any local environment. I’ve seen huge stands in unsuspecting homeowners’ yards, on roadsides (especially around recent construction), and in public parks—the plant climbs right over the top of existing vegetation, smothering it. It’s very difficult to eradicate, as the tenacious roots, spreading just under the soil, are lined with buds poised to send up new shoots as soon as the top-growth is mowed or pulled.
Swallowwort leaves are dark green and shiny, arranged in opposing pairs on the stem. They’re spade-shaped, wide at the base and narrowing to a sharp point, very similar to a lilac’s. The black swallowwort’s tiny flowers are perfectly-formed five-pointed stars in loose clusters, dark purple-to-black with a yellow center, and dusted with fine white hairs. On pale swallowwort, they’re a hairless, mauveish tan. It’s a member of the milkweed family, and its seed pods look just like miniature versions of a common milkweed’s.
Any invasive organism threatens the others in its environment through loss of habitat, but the swallowwort is especially dangerous to Monarch butterflies. Monarchs lay their eggs on a group of plants, Asclepias spp., that are also members of the milkweed family. When the caterpillars hatch, they eat the leaves, which contain compounds that are poisonous to would-be predators (a fact that is advertised by the adult’s brightly-colored wings).
Unfortunately, it’s easy for a female Monarch to get confused and lay her eggs on a swallowwort. The resulting caterpillars don’t survive. Some theories suggest that the caterpillars need the compounds found in the appropriate host plants in order to live, or they are poisoned by similar ones in the swallowworts, or they just find the leaves distasteful, won’t eat them, and starve.
If you have any swallowwort on your property, you should try to get rid of it now, before it gets any worse. As mentioned above, pulling and mowing don’t work, and digging it up is only effective if absolutely no traces of root are left either underground or sitting on top. Burning doesn’t kill the plants either. The only proven way of eradicating swallowwort is with repeated applications of chemical herbicides. Once it’s gone, don’t leave the soil bare—you’re only inviting a repeat infestation. The best defense is an environment of lush, healthy, desirable plants.
Copyright 2004, Jane Milliman