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Pale swallow wort found locally

Pale Swallow-wort, an invasive plant species, has been discovered on Huntington University’s campus by a local runner. The area around HU’s campus is the only confirmed case in the state of Indiana. The eradication process has started on campus property, but community members should look out for additional cases as it has begun to spread to the surrounding area. Photo provided.

Pale swallow-wort, an invasive plant species, was recently found in Huntington University’s campus woods making it the only confirmed population in Indiana.
Pale swallow-wort, or vincetoxicum rossicum, is native to Eastern Europe, near the Black Sea. It was likely brought to the U.S. in the late 1800s as an ornamental.

Pale swallow-wort’s Latin name, vincetoxicum rossicum, translates as ‘conqueror of poison’ as some species were used in traditional medicine to treat snake bites and various other ailments. It is also called ‘dog strangling vine’ but as it refers to multiple species in that genus, it is not a precise identification.

Currently, the area around Huntington’s campus remains the only confirmed site in Indiana where pale swallow-wort occurs.

The invasive plant was found by Joanna Stebing as she was running on the city bike trail between Gragg St. and Yeoman Park. Stebing is a biology student at Purdue Fort Wayne who is local to the area.

“As I’m running, I’m always looking at plants and zeroing in on what they are. I’ve run through there so many times, but I’ve never seen it when its blooming, so it caught my eye,” Stebing said. “I took a vine, and literally ran home with the vine so she could figure out exactly what it is.”

After identifying it as pale swallow-wort, Stebing sent photos to Colin Hobbs, biology professor at Huntington University, and others to figure out next steps.

The eradication process has started on the campus property, but there has been one iNaturalist identification across the road, meaning the plant is starting to spread off campus property. Stebing and Hobbs urge the community to keep a look out for other cases as it causes concerns for other plant and animal life.

“Generally, it has a negative effect on diversity,” Stebing said. “There are always multiple critters that use plants for food and shelter and the invasives tend to, since they haven’t developed in that area, cause detrimental effects on wildlife and pollinators.”

The main concerns with pale swallow-wort are:

•It is an invasive species, which means it is not native to the area, and can form thick monocultures along roadsides and hedges, and in old fields and forests. This means the pale swallow-wort will crowd out native species and degrade the natural habitat.

“Some invasives aren’t as aggressive or damaging to local woods, but certain ones will take over, filling up the ground, not leaving room for anything else to grow. And that seems to be the case for this,” Stebing said.

• Several studies have shown that swallow-wort can negatively impact the monarch butterfly populations.
Monarchs lay their eggs on the plant, since they have a hard time distinguishing it from their preferred host plant, most commonly milkweed. However, their larvae cannot survive on swallow-wort and quickly die.

• If it is not treated and eventually eradicated, large colonies will form an intertwining mat four feet tall making it difficult to walk through.
While it is not a vine, the top of the plant will act as a vine, wrapping around shrubs and each other making a tangled mess so thick you cannot walk through it.

• The entire plant, especially the root, is toxic to mammals, including humans, if it is ingested.
• It is currently considered one of the worse invasive plant species in the Canadian province of Ontario and in parts of New England.

• In New York, where the plant has its greatest density of occurrence, there has been reference of pastures, orchards, etc. being abandoned due to the severity of the infestation.
But there are steps to take before the pale swallow-wort overtakes the surrounding area.

The first step is to properly identify it as pale swallow-wort by:
• emailing a picture to chobbs@huntington.edu or jrs.arts@gmail.com,
• using a plant app such as iNatrualist, or
• posting a photo to Facebook groups such as “Indiana Native Plant Society” or “Nature in the Upper Wabash.”

Once you have correctly identified the plant, the eradication process must start sooner rather than later to prevent spreading.

“A lot of these plants spread quickly. These are wind dispersed seeds that can travel a couple hundred yards,” Hobbs said. “An individual plant probably produces several thousand seeds a year so they can spread quickly. But as with all invasive species, the sooner you start eradicating it, the better.” Some of the ways to eradicate it are:

• Hand pulling the plant only works if you dig up the root as well. This may work for one or two plants but can be too much work for larger groups.

• Mowing the plant down can help prevent seed production but will not kill the plant. If you can prevent the plant from blooming and producing seed, at least you can prevent the spread of the species.
The swallow-wort species have the capability to return to seed production status more quickly than other invasive plants post-mow and you must remain alert for a possible return.

• Herbicides, like glyphosate or triclopyr, are effective, but they may require follow-up treatments.

Pale swallow-wort was found in herbaria samples from the University’s botanical garden records in 1959 and 1961 listed as occurring in the campus woods, where it has been discovered recently.

There is speculation that this group of swallow-wort was escaped from the Huntington University botanical gardens which was started in the 30s.
There were three herbarium specimens collected in 1959 and 1961 by Norlan C. Henderson, former biology professor at what was then Huntington College, where he stated they were collected ‘on the campus of Huntington College.

One of these specimens was sent to Illinois where it was recorded and the other two are remain in the Huntington University Herbarium.

“Where the botanical garden was located, which is no longer there, is directly adjacent to where we found specimens on the bike trail and where there are other specimens of that species scattered around the campus woods,” Hobbs said.  “It seems probable but there is no hard evidence.”

However, Stebing’s discovery is the first sighting since those samples were taken, other than one iNaturalist recording on Stultz road in May of 2021 not far from the area Stebing rediscovered it.
Hobbs has been managing invasive plant species in the HU campus woods for nine years.

“Even if we kill every single plant that’s growing right now, there’s still seeds that will come back next year, and we’ll have to go back and look for those. So, it’s not a one-time situation, you have to stay on top of it,” said Hobbs.

“If you truly want to eradicate it, which is hard to do, you have to pay very close attention for five to ten years checking on it from time to time. But you can knock it back a lot, not doing anything is much worse. If you take 90 percent of it out the first year, that’s a huge difference compared to just ignoring it.”

Hobbs and Stebeing have put down 16 gallons of herbicides within two outings, it is the beginning of an ongoing process.