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Carpenter Costin Blog

Invasive Vines: Black Swallow-Wort

What is Black Swallow-Wort?

Black swallow-wort and it’s “twin” Pale swallow-wort are two invasive vines currently growing in New England, and are deemed invasive in Massachusetts and Connecticut. These herbaceous, twining vines grow three to six feet, with opposite, shiny leaves 2” to 4” long. 

imageThe flowers on swallow-wort are dark, usually purple black on Black, and Maroon on Pale swallow-wort, and produces seedpods 1.5” to 3” long, bearing numerous seeds. Due to a strong fibrous root system, eradication by digging is difficult, as plants can regenerate from root fragments.  A healthy stand of swallow-wort may produce between 1000 and 2000 seeds per square meter, per year, depending on sunlight.  Swallow-worts grow in full sun to partial shade, and are more invasive in full sunlight.

Problems They Cause

Black Swallow-wort and Pale Swallow-wort invade planting beds, climbing up your trees and shrubs and even under your storm windows. According to, http://nyis.info/invasive_species/swallow-wort/ they are two distinct species but share similar characteristics. A similar characteristic that they both share is that they are both perennial climbing vines. Which means that they don't just die over time, they just keep reoccurring through the thousands of seeds they produce. Once the Black Swallow-wort settles in, they form extensive patches that overgrow and smother the native vegetation.

How they affect Monarch Butterflies

Besides its ability to displace native plants, swallow-worts are also interfering with the reproductive success of the Monarch Butterfly, and possibly other species as well. 

Monarchs normally lay their eggs on native milkweeds, which are disappearing due to competitive pressure from swallow-worts. In addition, Monarch eggs which are laid on Black swallow-wort have nearly 0% hatching success. This is because when the larvae are born they can't ingest or use the toxin that is in either the Black Swallow-wort or the Pale Swallow-wort in which they won't be able to survive. 

How to control?

Control is particularly difficult, because of the rhizome root system and fibrous root. Early detection and physical removal is recommended as the best control method. It is crucial to dig out the roots completely. Chemical methods are rarely 100% effective, and there is no biological control at present. Being able to identify and remove the individuals before they seed and spread is an important tool in the effort to stop the species.

If you have any questions, or you are interested in any of our tree services, please contact us at 877-308-8733, or request a free consultation. We look forward to hearing from you!

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Photo courtesy of Becky Gallery, Harpswell Heritage Land Trust

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