Black Swallow-wort

Spread the Word, Not the Seed

Why Are We Worried About Black Swallow-wort?

Black Swallow-wort is a fast-spreading invasive vine that chokes out other plants and small trees. Because the fruit of Black Swallow-wort resembles milkweed, butterflies lay their eggs on it. The larvae hatch, eat the Black Swallow-wort leaves, and die from the toxins in the leaves, causing a loss in Monarch butterflies! Studies find that 100% of Monarch larvae hatched on Black Swallow-wort will die. Also, Black Swallow-wort is allelopathic, meaning it releases chemicals that decrease the ability of nearby plants to grow.

What Does Black Swallow-wort Look Like?

Black Swallow-wort (Becky Gallery photo)

Click here to download a fact sheet about identifying and controlling Black Swallow-wort.

Black Swallow-wort is an aggressive invasive vine that has already arrived and become established at Land’s End at the tip of Bailey’s Island in Harpswell.

This invasive plant imitates milkweed and causes problems for pollinators, especially monarch butterflies.

Black Swallow-wort has dark green, shiny, lance- or heart-shaped leaves that have smooth edges and are 2-5″ long. Leaves are arranged opposite each other along the stem. The stem is green, thin, and twines around other plants. The fragrant flowers appear from June to September and are purplish-brown, 1/4″ wide, with 5 petals. Late in the season, slender green pods (1.5-3″ long) form, turning dark brown when ripe.

What Can I Do About Black Swallow-wort?

  • You can follow these steps to control the Black Swallow-wort that you find:
    • Cut off the purple flowers when they appear beginning in June.
    • Dig out a large area around the base of small plants before seed pods appear; it is important to remove all the roots. Mowing is not recommended, because it only encourages re-sprouting. Repeated digging and monitoring are recommended during the growing season to prevent seed pods from forming.
    • Cut and bag seed pods when they appear in late summer.
    • Herbicide treatment, if permitted: Spray with Ortho Brush-B-Gone just when pods are starting to form (not earlier). Repeat 3 weeks later; repeat for 2-3 years. Certified professionals may spray 2% glyphosate (Rodeo) and .5% triclopyr (Garlon-3A) tank-mixed with surfactant (Cide-Kick II) just when pods are starting to form; repeat after 3 weeks and for 2-3 years.
    • Bag and dispose of all plant parts in the trash dumpster at the upper part of the Transfer Station, near the scale.
  • You can join us in our removal efforts by signing up for one of our community work days listed in the 2018 HIPP Events and Work Days page of this website.

Are There Native Plants I Can Use to Replace Black Swallow-wort?

Milkweeds are good alternatives to plant because Monarch butterflies need milkweeds for their life cycles. Try Swamp Milkweed (Asclepias incarnata), Common Milkweed (Asclepias syriaca), or Butterfly Weed (Asclepias tuberosa). You can also plant native Trumpet Honeysuckle vine (Lonicera sempervirens).

What Is HIPP and What Are We Doing?

The Harpswell Invasive Plant Partnership (HIPP) is a volunteer organization formed in 2014.

  • We conduct surveys to identify invasive plants in Harpswell.
  • We work to remove or control invasive plants on lands owned by the Town and by the Harpswell Heritage Land Trust, and along the edges of the major highways in Harpswell.
  • We offer public programs to educate Harpswell residents about the dangers of invasive plants and how to control them.
  • We help Harpswell residents identify invasive plants on their properties and suggest strategies to control them.