Black swallow-wort (Cynanchum louiseae) is an invasive herbaceous vine that hails from southwestern Europe and was first discovered in New York in the 1890s, along with its equally damaging sister to the East, pale swallow-wort (Cynanchum rossicum). It is a perennial vine, meaning it has a robust root system and has a life cycle that exceeds two years. It has pointed, dark green oppositely paired leaves and small, five-petaled flowers that range from a deep purple to black in color. Its relation to the milkweed carries a familial similarity in its seed pod, which houses dozens of thin, white feathery strands that allow it to be easily picked up and dispersed by the wind.

  Also known as the “black dog-strangling vine,” it is indeed a     formidable opponent of our native species. It reproduces by     generating an abundance of seeds in each stem, and if that     wasn’t enough, more stems that grow from buds appearing       on the root crown. It thrives in high-light environments, such     as open fields, pastures, abandoned farms, and roadsides,       and can survive in a variety of soil conditions. This makes it     easy for the vine to cause irreparable damage to Christmas     tree farms and decrease the value of farmland. While it has       been in North America for over a hundred years, it has only       become a threat to native plant habitats and threatened or       endangered species in the past twenty years. In particular, swallow-wort contributes to the decline of the native monarch butterfly population. Its relation to milkweed, where the monarch typically lays its eggs, confuses the butterfly; so much so, that it will lay up to 15% of its eggs on black swallow-wort by mistake, effectively killing the larvae.

One of the greatest issues with black swallow-wort is that we don’t know why it’s invasive. This makes management and control very difficult. Both mechanical and chemical methods have proved somewhat ineffective, and expensive as chemical control takes several years of monitoring and repeat application. Additionally, black swallow-wort can be found weaving in and around native plants, making it difficult to target just the invasive species with herbicide. Mechanical or manual methods like mowing and pulling from the root are only useful in minimizing seed production or for smaller patches, respectively. Even then, it would take years of multiple removals within a season to see any results. To this end, a study was done in Bear Mountain State Park from 2008-2014 that compared clipping, pulling, and insect-defoliation as control methods. It found that the only method that was remotely successful was clipping the leaves and stems four times per season. After years of research and scientific study, it seems that biological control is the final step. To be effective, there must be introduction of natural enemies of a species where they don’t normally occur. The species will seek out what is familiar to them as opposed to our native species. Therefore, an insect native to black swallow-wort’s natural habitat would need to be introduced.

 Enter Hypena opulenta, a moth whose native distribution overlaps with pale swallow-wort in the Ukraine, which has a similar climate to both southwestern Europe and the northeastern US. This makes it an ideal candidate to be used as a biological control method. In 2013, after sending proposals to both the Canadian and United States government, the Technical Advisory Group for Biological Control Agents of Weeds was able to successfully petition for release the moths in Canada but not in the U.S. It has been four years, but just last month the USDA APHIS has issued an Environmental Assessment regarding the distribution of permits to release the moths in America that is open for public comment. Go here to express your approval or concerns, and help us continue the fight against black swallow-wort and all invasive species!                                                                          

Averill, Kristine, et al. “Survival, Growth, and Fecundity of the Invasive Swallowworts (Vincetoxicum Rossicum and V. Nigrum) in New York State.” Invasive Plant Science and Management, vol. 4, no. 2, 2011, pp. 198–206. Milbrath, Lindsey, et al. “Tolerance of Swallowworts (Vincetoxicum Spp.) to Multiple Years of Artificial Defoliation and Clipping.” Invasive Plant Science and Management, vol. 9, no. 1, 2016, pp. 1–11.

Young, Jim, and Aaron S. Weed. “Hypena Opulenta (Erebidae): A European Species for the Biological Control of Invasive Swallow-Worts ( Vincetoxicum Spp.) in North America.” The Journal of the Lepidopterists&Apos; Society, vol. 68, no. 3, 2014, pp. 162–166.

Field release of the leaf-feeding moth, Hypena opulenta (Christoph) (Lepidoptera: Noctuidae), for classical biological control of swallowworts, Vincetoxicum nigrum (L.) Moench and V. rossicum (Kleopow) Barbarich (Gentianales: Apocyanceae), in the contiguous United States. Environmental Assessment, USDA, June 2017.

"Invasive Vines Swallow-up New York's Natural Areas" Cornell Chronicle, April 2014.