Black swallow-wort (Cynanchum louiseae)


Black swallow-wort (Cynanchum louiseae) Weed.

Cynanchum louiseae, a species in the milkweed family, is also known as Black swallow-wort, Louise’s swallow-wort, or Black dog-strangling vine, Cynanchum louiseae is a species of plant that is native to Europe and is found primarily in Italy, France, Portugal, and Spain.[3] It is an invasive plant species in the northeastern United States, parts of the Midwest, southeastern Canada, and California.


Cynanchum louiseae is a perennial, herbaceous vine with oval shaped leaves that have pointed tips. The leaves are 3-4 inches long an 2-3 inches wide and often occur in pairs on the stem. The flowers have five petals that are star-shaped with white hairs. The flowers range in color from dark purple to black. The fruit of Cynanchum louiseae is slender, tapered pods that range in color from green to light brown.


Cynanchum louiseae tends to grow in upland areas and is tolerant to variable light, salt, and moisture levels. In the United States, Cynanchum louiseae is often found in abandoned fields, hedgerows, brushy areas, woodlands, river banks, transportation corridors, quarries, agricultural fields, and gardens. In gardens, Cynanchum louiseae is seen as a weed.


Cynanchum louiseae emerges in the spring and flowers during June and July. Cynanchum louiseae is self-pollinating. Seed pods form throughout the summer. The number of pods formed is directly linked to the amount of light the plant is exposed to. If there is a higher level of light, then there are more seed pods. If there is a lower level of light, then there are fewer seed pods compared to a plant exposed to a higher level of light. Its seeds begin to be released by mid-August and continue to be dispersed into early October. Each seed is polyembryonic and contains about one to

Distribution of Black swallow-wort (Cynanchum louiseae) in North America shown in Green.

four embryos per seed. Polyembryonic seeds increases Cynanchum louiseae’s chance of survival. Seeds also use “parachutes” in order to be dispersed by the wind over large distances. In addition to seeds, for reproduction, Cynanchum louiseae also uses rhizomes as a method of reproduction, meaning that the plant clones itself and produces new plants. After seed dispersal, the plant dies to the ground in the winter and returns in the spring.


Black swallow-wort invasive species advisory sign, Lake Allen, Cambridge Township, Michigan

The first group of Cynanchum louiseae was recorded to be in Ipswich, in Essex County, Massachusetts in 1854. In 1864, a plant collector recorded that it was “escaping from the botanical garden where it is a weed promising to be naturalized”. Thus, Cynanchum louiseae escaped from a garden in the Cambridge area of Massachusetts and naturalized in the surrounding states and is still spreading today.

Ecological implications:

In the United States and Canada, Cynanchum louiseae is a threat to native species because it crowds out native species. For example, Cynanchum louiseae can completely replace a field of goldenrod. Crowding out other species results in a reduced habitat for wildlife and some species may become endangered because they do not live in the correct habitat. Cynanchum louiseae threatens the rare limestone pavement barren ecosystems by crowding out plants that the surrounding wildlife needs. Cynanchum louiseae may also decrease bird presence in grasslands, which may cause insect species populations to increase. In Vermont, Cynanchum louiseae crowds out the endangered species Jessop’s milk vetch. In Rhode Island, Cynanchum louiseae reduces the effectiveness of electric fences, which may cause livestock to be put into danger or lost. In addition, Cynanchum louiseae crowds out another species of milkweed that monarch butterflies use in order to reproduce. When monarch butterflies try to reproduce using Cynanchum louiseae, the larvae do not survive. Thus, Cynanchum louiseae threatens populations of monarch butterflies. Overall, Cynanchum louiseae reproduces effectively and can easily take over various habitats in a short amount of time. It can easily take dominance over native species’ habitats. Most of the possible implications of Cynanchum louiseae changing the physical structure of various ecosystems are yet to be known.


Close up of Black swallow-wort (Cynanchum louiseae) Weed Berries.

There are four methods of management that can possibly be used for the management of Cynanchum louiseae. These methods are chemical, manual, mechanical, and biological. Only the chemical, manual, mechanical methods are actually used in the United States and Canada. The biological method may be used in the future. Overall, early detection and removal is the best management.


The best chemical management over Cynanchum louiseae is through the use of systemic herbicides. Systemic herbicides prevent seeds from being viable and, as a result, the next generation will not exist. Garlon 4 (tridopyr ester) and RoundUp Pro (glyphosate) are the main systemic herbicides that are used to control Cynanchum louiseae. The systemic herbicide is sprayed on the plant after flowering has begun. If the herbicide is used after seed pods have formed, then the herbicide is less effective because viable seeds may form. The most effective treatment using systemic herbicides is through a cut stem application, which is applying the chemical to cut stems.


Manual management is the removal of Cynanchum louiseae from the ground by digging up its roots so that the plant cannot reproduce.


Mechanical management is the mowing down of Cynanchum louiseae. This method does not stop growth, but it does stop seed crops. No seed crop means no reproduction and no new generation.


Biological management is the use of Cynanchum louiseae’s natural enemies to lower the population of Cynanchum louiseae. In the United States, Cynanchum louiseae has no natural enemies. In its native European regions, Cynanchum louiseae has natural enemies, such as certain caterpillars, beetles, and diseases. Researchers at Cornell University and the USDA are researching into the use Cynanchum louiseae’s natural enemies as a way to control Cynanchum louiseae. The use of natural enemies is controversial because the implications of adding more non-native species to threatened areas in unknown. Using Cynanchum louiseae’s natural enemies may result in many new problems.

Sourced From: