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Swallow Wort - Overview

(Information below extracted from: 1. "A Review of the Biology and Ecology of Three Invasive Perennials in New York State: Japanese Knotweed, Mugwort and Pale Swallow-wort" by Leslie A. Weston, Jacob N. Barney and Antonio DiTommaso and 2. The Nature Conservancy Element Stewardship Abstract for Pale Swallow-wort).

Pale Swallow Wort

Pale swallow-wort is native to the Ukraine region of Eastern Europe. It was introduced to the U.S. about 120 years ago and is currently expanding its range at an alarming rate. The seeds are wind-borne which facilitates long-distance dispersal. It often is associated with disturbed areas; once established, it tends to move readily into nearby, less disturbed habitats. It is speculated that pale swallow-wort’s effect on the composition and diversity of the soil microbial community may contribute to the displacement of the resident vegetation.

Pale swallow-wort is well-established in New York State. In the past decade, Christmas tree growers have reported increased pressure from this invasive plant. Also, the New York State Forest Owners’ Association has expressed concern that infestations in central New York may be negatively impacting forest regeneration. Some landowners have abandoned horse pastures after trying to control swallow-wort for several years. It is also beginning to invade alvar communities in eastern Ontario, Canada and Jefferson County, New York. This plant may also have a negative impact on the monarch butterfly, causing a decline in the monarch host plant availability. In addition, research has shown a correlation between increased swallow-wort and decreased grassland bird presence.

For much more information about Pale Swallow-wort: "A Review of the Biology and Ecology of Three Invasive Perennials in New York State: Japanese Knotweed, Mugwort and Pale Swallow-wort" by Leslie A. Weston, Jacob N. Barney and Antonio DiTommaso

Black Swallow Wort

Black Swallow-wort is related to Pale Swallow-wort. Both plants are in the milkweed family and grow in similar habitat. Black Swallow-wort is native to Western European Mediterranean regions. In New York State, Pale Swallow-wort is established in the Great Lakes Basin and black swallow-wort is established in the Lower Hudson Valley. However, the two plants clearly have some geographical overlap: there are voucher specimens for Black Swallow-wort as far west as Erie County and voucher specimens for Pale Swallow-wort as far south as Nassau County.