Black Swallow-wort (Cynanchum louiseae)

Originating in southwestern Europe, this plant made its way to America due to preference as an ornamental plant. It was noted to be escaping from gardens in the late 19th century, and is now widespread in the northeast US and southeast Canada, with some presence in the Midwest. An herbaceous twining vine (sometimes known as “dog-strangling vine”) with oblong leaves up to 5 inches long that taper to points at the end, it is decorated with very small dark purple flowers, with seed pods that are up to 1.5 inches long that can be slender or plump. The seeds are spread by wind once outside of the seed pods. The plant grows very fast and thus can create dense patches that will cover and shade out other plants. The plants, which are related to milkweed, are extremely toxic to livestock and monarch butterfly larvae (which can sometimes be fooled into laying their eggs on the plants).

The seeds can drift very far, making control difficult, but established plants can be handled effectively. Hand uprooting is effective, as well as cutting or mowing more than once a season. Application of herbicides to foliage is also effective in reducing growth and spread of the plant.