Black Swallow-wort & Pale Swallow-wort
Perennial vines from Europe, black swallow-wort (Cynanchum louiseae) and pale swallow-wort (Cynanchum rossicum) can grow up to 8 feet long by late summer. Black swallow-wort has small purplish flowers, while pale swallow-wort has pinkish flowers. Both have long green pods and produce wind-borne seeds.
Black swallow-wort and pale swallow-wort (which has pinkish flowers) invade fields and field edges. Black swallow-wort may also invade woodlands. Close relatives of milkweed, these species may interfere with monarch butterfly reproduction.
Remove seedlings and young plants with hand pulling, and remove small numbers of mature plants with digging. Follow-up control of seedlings will likely be needed in subsequent years. Frequent mowing can suppress populations in fields, but plants will persist and some may still produce seeds. Systemic herbicides can be used to control large infestations; several years of treatment will likely be needed, because its seeds persist in the soil. Always read and follow the directions on the label when using herbicide.