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July 7, 2021
July Weed of the Month: Pale Swallow-wort
Christina Basch, Minnesota Department of Agriculture
There are over 2,900 described species in the milkweed subfamily (Asclepiadoideae) containing herbs, shrubs, vines, and trees. Minnesota is home to 14 native milkweeds, all which are herbaceous perennials. Last month, the Minnesota Weed of the Month highlighted rough potato, a newly discovered vining milkweed from east Asia. Pale swallow-wort (Cynanchum rossicum) is another newly observed vining milkweed native to southwest Russia and Ukraine.
Pale swallow-wort is closely related to black swallow-wort which is a designated Prohibited Eradicate Noxious Weed with limited populations found around the Twin Cities area. Pale swallow-wort was introduced to the United States as a cultivated plant. It is linked to the decline in monarch butterfly populations on the East Coast. The foliage is toxic to monarch caterpillars.
A risk assessment from 2012 evaluated whether pale swallow-wort could survive in Minnesota. Though it concluded that pale swallow-wort was unlikely to establish and become a serious invasive pest, two populations were discovered in 2020 in Scott County. Both populations are documented to be reproducing and spreading into adjacent areas. We need your help. Please be on the lookout for this potentially invasive pest in Minnesota.
How to Identify
Pale swallow-wort is an herbaceous, perennial vine that dies back to the ground each winter. Leaves are opposite with smooth edges and a glossy green exterior. Flowers have five petals that curl around the edge. Flowers are small with a diameter of only 1/8 inch and form smooth slender seed pods roughly 2 inches in length.
 Pale Swallow-wort flower
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 Black Swallow-wort flower
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 Pale swallow-wort seed pods
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 Pale swallow-wort leaves
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Reporting
If you suspect you have found pale swallow-wort, note the exact location with the address or GPS coordinates. If it is possible, take digital photos of the flower, vine, leaves, and fruit, and email them to the Minnesota Department of Agriculture (MDA) for identification.
Infestations can be reported to one of two places:
- The MDA by email at arrest.the.pest@state.mn.us or voicemail at 1-888-545-6684
- Directly to EDDMapS through the EDDMapS app on a smartphone or tablet, or at EDDMapS.org
MEDIA: For more information on Weed of the Month, contact Allen Sommerfeld, MDA Communications, at allen.sommerfeld@state.mn.us or 651-201-6185
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