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Black and Pale Swallow-worts

Overview

Black and pale swallow-worts  (Vincetoxicum nigrum, Vincetoxicum rossicum ), also known as “dog-strangling vines,” are perennial, herbaceous vines that grow from 2 to 6 1/2 ft in length.

Black swallow-wort is native to Europe near the Mediterranean Sea, while pale swallow-wort is native to Ukraine and parts of Russia. Although swallowwort isn’t highly valued as a horticultural specimen, it escaped cultivation in the 1800s.

Impacts

  • Swallow-worts aggressively choke out desirable species. They are problematic in Christmas tree plantations, perennial crop fields, pastures, roadsides, disturbed areas, and natural areas.
  • Pure stands of swallow-wort suppress the establishment of other species and interfere with forest regeneration.
  • Related to milkweeds, swallow-worts are toxic to livestock, deer, and monarch butterfly larvae, which are sometimes fooled into laying their eggs on these plants, but their larvae do not survive. Learn more about the impacts swallow-worts have on monarch butterflies.
  • Habitat/Distribution:
  • Both species of swallowwort thrive in sunny, disturbed areas, roadsides, fencerows, and shaded wooded areas. Pale swallow-wort is heavily present throughout the St. Lawrence Eastern Lake Ontario (SLELO) region, particularly in Jefferson County, where it infests areas like the Chaumont Barrens. It is widely established at Robert Wehle State Park in Henderson, NY. It can also be found along roadsides, in forests, and in old fields across the region.

Identification

Pale Swallow-wort (Cynanchum rossicum syn. Vincetoxicum rossicum)

Leaves:  Leaves are opposite in arrangement, oval to wedge-shaped with pointed tips. Generally, the leaves are 2.5″ to 4.5″ long and 2″ to 2.75″ wide, glossy, and medium green in color. In summer, the leaves begin to display a warm, yellow color.

Pale swallowwort leaves. Photo credit, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Flowers: The star-shaped flowers are small and fleshy, with 5 pink to reddish colored petals. They are borne in loose clusters and are visible in late May through mid-July.

 

Pale swallowwort flowers. Photo credit, Rob Routledge, Sault College, Bugwood.org.

Black swallow-wort (Cynanchum louiseae syn., Vincetoxicum nigrum)

Characteristics are similar to pale swallow-wort, but black swallow-wort leaves are dark green, shiny, and larger in size ranging from 3-4″ long and 2-3″ wide.

Black swallowwort leaves. Photo credit, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Flowers are dark purple/blackish in color and bloom from June to July.

Black swallowwort flowers. Photo credit, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

 Fruit/Seeds: The fruit of both pale and black swallowworts are smooth, slender, pointed pods that look similar to a milkweed pod. The pods are light green in color and are frequently borne in pairs. They are abundant during July and August. Like milkweed, the pods open in late summer, disseminating large numbers of downy seeds. Each pod can produce up to 2,000 seeds per square yard.

Black swallowwort seed pods. Photo credit, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Pale swallowwort seed pods opened. Photo credit, John M. Randall, The Nature Conservancy, Bugwood.org.
Pale swallowwort seed pods after the growing season. Photo credit, Leslie J. Mehrhoff, University of Connecticut, Bugwood.org.

Management: 

 

Prevention

  • Stay out of infested areas during seed dispersal to prevent seed dissemination to unaffected areas.
  • Clean boots, ATVs, and other equipment before and after entering new areas. 

Physical/Mechanical Control:

  • Monitor for populations in June. Plan removal efforts for found populations to occur before seedpods open in late summer.
  •  Initial control efforts should concentrate on plants in sunny areas since they will produce the most seeds.
  • Small patches can be dug out by hand.
  • Removing roots decreases the likelihood of new growth.
  • Place all plant parts inside a tied black bag in the sun for 2 weeks, and dispose of at an approved landfill. 
  • Large stands can be managed by consistent mowing when pods are very small  (May-July). 
  • Controlled burning is not effective and may improve site conditions for seedling establishment.

Chemical Control:

  • Triclopyr or glyphosate can be applied to foliage prior to seed set typically in late June to mid-July for the SLELO region.
  • The use of surfactants helps herbicides penetrate the waxy leaf coating. Cut-stem treatment with glyphosate is effective but labor-intensive.
  • Use of systemic “Round-Up” herbicide is also effective in removing swallow-wort.
  • Regional response teams have found success using a foliar application of glyphosate (Rodeo, Accord XRT-II, etc.) or triclopyr (Garlon 4 Ultra) at a 2 to 3% solution.

Resources:

SLELO PRISM GOALS

PREVENTION
Prevent the introduction of invasive species into the SLELO PRISM.

EARLY DETECTION & RAPID RESPONSE
Rapidly detect new and recent invaders and eliminate all individuals within a specific area.

COOPERATION
Share resources, including funding personnel, equipment, information, and expertise.

INFORMATION MANAGEMENT
Collect, utilize, and share information regarding surveys, infestations, control methods, monitoring, and research.

CONTROL
Control invasive species infestations by using best management practices, methods and techniques to include: ERADICATION (which is to eliminate all individuals and the seed bank from an area), CONTAINMENT (which is reducing the spread of established infestations from entering an uninfested area) and SUPPRESSION which is to reduce the density but not necessarily the total infested area.

RESTORATION
Develop and implement effective restoration methods for areas that have been degraded by invasive species and where suppression or control has taken place.

EDUCATION & OUTREACH
Increase public awareness and understanding of invasive species.

INNOVATION
Develop and implement innovative technologies that help us to better understand, visualize, alleviate or manage invasive species and their impacts or that serve to strengthen ecosystem function and/or processes.

SLELO TEAM

Rob Williams
PRISM Coordinator

Megan Pistolese
Outreach and Education

Brittney Rogers
Aquatic Invasive Species

Robert Smith
Terrestrial Invasive Species

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