Jennifer Forman Orth
Cynanchum louiseae Kartesz and Gandhi
Milkweed family (Asclepidaceae)
Origin: Endemic to southwestern Europe, primarily in the Iberian Peninsula, southern France and northern Italy
Also known as black dog-strangling vine, this species was introduced as an ornamental plant. Early North American collections include one from Essex County Massachusetts in 1864, stating “escaping from the botanic garden where it is a weed and promising to become naturalized” and in 1867, Gray’s Manual of Botany, 5th edition, reported it as “a weed escaping from gardens in the Cambridge Massachusetts area.”
Distribution and Habitat
This species occurs in southern and eastern Ontario and southern Quebec, around Montreal, and in the U.S., primarily in the Northeast and Midwest with an additional occurrence in California. Recent observations of infestations along the Appalachian Trail in Pennsylvania are a concern due to the potential for spread. It occurs primarily in upland areas in forest understory, pastures, old fields, shores, flood plains and disturbed areas. Most populations occur in areas dominated by limestone bedrock, although it is sometimes found on rock substrates or sandy areas of low pH. It is tolerant of a wide moisture regime and habitats subject to hydrologic extremes such as alvar communities, rocky outcrops and coastal areas are often colonized. Although tolerant of some shade, it flourishes in sunny open areas and shrubby habitats and once established moves into less disturbed habitats. Well-drained, stony soils are often densely colonized.
Black swallow-wort is a threat to native flora because of its vigorous growth and the formation of dense patches that cover and shade out native plants and reduce invertebrate and vertebrate biodiversity. Establishment of C. louiseae is reportedly threatening the endemic Jessop’s milkvetch (Astragalus robbinsii) at Windsor, Vermont, on ice-scoured banks of the Connecticut River.
Description and Biology
Prevention and Control
Do not plant this or other exotic swallow-worts. Plants can be pulled by hand or cut or mowed once or twice per season, or dug up, removing the roots. For large infestations, the most effective control is usually achieved with herbicides applied to foliage, because manual and mechanical control are difficult, labor-intensive and time-consuming. Systemic herbicides (e.g., glyphosate) are most effective because they kill the entire vine including the roots (see Control Options). No biological control agents are available for this species.
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