Two very destructive invasive vines are spreading rapidly through large areas of New England, New York, and Ontario, and both are a threat to Monarch butterflies. I've been battling black swallow-wort (left) at my vacation place in MA for more than 10 years. It's a true nightmare and nearly impossible, I think, to eradicate. (Any suggestions?) According to the USDA's Agricultural Research Service, black swallow-wort (Vincetoxicum nigrum) and its cousin, pale swallow-wort (V. rossicum) are members of the milkweed family and are a threat to Monarch butterflies. The invasive vines may be replacing common milkweed in many areas, upon which monarch larvae feed.(image to right). The larvae are unable to survive on either of the swallow-wort species.
Both vines are of European origin, where they have natural insect and disease enemies. According to entomologist Lindsey Milbrath of the Agricultural Research Service's Plant Protection Unit in Ithaca, NY, neither vine appears to have any natural enemies in the US (so far, anyway) to halt their spread. Milbrath reports that both vines have strong natural poisons that could limit natural enemies and keep deer and cattle away from them.
The pink flowering pale swallow-wort is spreading in open fields and in forest under-stories throughout central and upstate New York, near the Great Lakes, and in Canada. The purple-flowering black swallow-wort spreads rapidly in open areas and is found in New York's Hudson Valley and on Long Island, and throughout New England.
Scientists at ARS and Cornell University have now launched studies in an effort to find ways to halt these two horrendous invasives. They are known as "dog-strangling" vines, and believe me, that's an apt description.
(click on images for larger view)
(Monarch image: Peggy Greb, courtesy USDA)