New invasive vine strangling plants in Jefferson County

Black Swallow-wort, a twining vine with dark purple star-shaped flowers, has recently been found in several locations in the Fort Atkinson area. This aggressive non-native vine can completely take over upland sites, strangling native trees and shrubs and cascading over flowers and grasses, blocking out the sunlight. Suzanne Wade, UWEX Rock River Basin Educator for Natural Resources wants to alert residents throughout the basin of this potential menace to our natural habitats. Wade states “This plants, also known provocatively as ‘dog strangling vine’, has previously been documented in a few locations in Rock, Walworth and Waukesha counties, but recent discoveries by Cindy Wagner of Local Landkeepers, LLC shows it is well established in several locations in Fort Atkinson. We also need to know if it has spread further into Jefferson, Dodge or Dane counties.”

Cindy states, “This is quite a nasty viney invader that is hard to eliminate once it is established. It is in the milkweed family and its seeds float on the wind, incredibly each seed can produce three plants! We need to catch this before the seeds start to disburse. Thick infestations in full sun can produce 2,000 seeds per square meter. I’ve found it along Messmer Street and in the West Park subdivision, which means it must be in other locations as well.” Cindy continues, “Help prevent the spread by pulling the plants and sending them to the landfill in black plastic bags, stick a piece of masking tape on the bag, and mark it invasive plant.”

When black swallow-wort covers old field habitats of goldenrod and grasses it changes the physical structure of the plant community and most likely results in a decline in grassland bird presence. The monarch butterfly is also affected since the monarch caterpillar feeds exclusively on milkweed. Research shows that the butterfly will cue into black swallow-wort and lay eggs, but the larvae do not survive.

Wade explains, “Now through September is the best time to monitor for black swallow-wort as in late summer the plants turn golden yellow and pods become prominent. All pods should be removed before they open, and then burned or landfilled to prevent seed release”.

Eradication is difficult once a colony is established because plants form a dense, knobby mass of underground roots. Initial control efforts should concentrate on plants in sunny areas since they produce the most seeds. Triclopyror glyphosate with a surfactant can be applied to foliage during the growing season. Cut-stem treatment with glyphosate is also effective but labor intensive.

For a fact sheet on black swallow-wort contact the UWEX Jefferson County office at 920-674-7297 or go to dnr.wi.gov/invasives/fact/swallowwort_black.htm. If you find a plant you think is a black swallow-wort, either contact Suzanne Wade, at the Jefferson County UW-Extension office or go to http://dnr.wi.gov/invasives/futureplants/index.htm to learn how to report it. This website also shows other plants to be on the look-out for.