What Is Black swallow-wort?
Black swallow-wort (cynanchum louiseae) is a species in the milkweed family, but exactly the opposite of the beneficial milkweed. It is highly invasive and on the top ten worst weeds to have in your yard. It is also known as the ‘black dog-strangling vine.’
Native to Europe, it has invaded New Hampshire and most of the United States. It can grow in variable light, salt and moisture conditions. It grows on the sides of roadways, in woodlands, agricultural fields, virtually anywhere with any soil or sand of any kind.
You will recognize the black swallow-wort vine by the 3 inch oval-shaped, shiny, dark-green leaves with pointed tips and star-shaped, dark purple or black flowers with five petals and white hairs. This is the time of year that the flowers begin too turn to seed pods. Similar to milkweed, the parachute-like seeds are easily dispersed by the wind.
It is a perennial that dies back in the winer but returns in the spring. It threatens native species because it crowds them out and can destroy native habitiats in a short amount of time, including those important to monarch butterfly reproduction. Monarch butterflies may lay thier eggs onthe black swallow-wort but the larvae do not survive.
Controlling An Invasive Vine
To control this invasive vine you must remove it. Unfortunately, it has an extensive rhizome ( a thick underground horizontally growing stem) system and if you just pull the plant out by the root without removing or killing the rhizome, new shoots will continue to grow. You can at least control the spread of the weed by cutting the plant and disposing of it in the trash, NOT compost. This action must be taken immediately if you see weed seeds forming. This method does not prevent growth, but it at least means that the swallow-wort is not propagating further. Cutting or mowing over several seasons may be effective in reducing the plant.
If you see this plant in your yard, it is important to eradicate it immediately before it becomes an even greater threat. Please share this information with neighbors and friends!