Black SwallowWort

Black swallowwort is a perennial vine that can grow up to 6.5 feet in length. It has oppositely arranged leaves that are dark green and oval, and the flowers appear as black-purple clusters of 6 to 10 flowers with five petals each. The fruit forms in pods, like milkweed pods, which are two- to three-inches long, and they split to reveal small seeds with white, tufty hairs. The hairs allow the seeds to be readily dispersed by wind. The vine has rhizomes that sprout new plants.

Black swallowwort tolerates a wide range of light and moisture conditions and invades a wide variety of upland habitats including fields, field edges, and forests, forming dense stands that crowd out other vegetation. It produces large numbers of wind-dispersed seeds. Swallowwort is closely related to common milkweed and may interfere with the life cycle of monarch butterflies.

Hand digging or pulling may be possible for small populations of swallowwort. Established vines have large root crowns that will resprout if not removed. Mowing prior to seed production may help to prevent the spread of swallowwort, but swallowwort appears capable of surviving even in lawns that are mowed weekly. Glyphosate-based and triclopyr-based herbicides applied as a foliar spray are effective, but the treated plants often survive for the remainder of the growing season. Herbicide treatment should be performed before July 1st to prevent seed production. Follow-up treatments may be needed for several years to control seedlings.

In Newburyport’s yard waste center, any cuttings should be contained in a brown paper leaf bag with a closed top and placed in the designated location per the attendant or cuttings may disperse and reestablish. You may also call the Sustainability Office at 978/499-0413 to get advice on the best disposal options for invasive plant cuttings.