An invasive vine not reported in North America for more than 60 years turned up this summer in a small central Minnesota city — a discovery that has local and state officials puzzled as they work to eradicate the plants.
Rough potato — a type of vining milkweed native to several countries in eastern Asia — was found this summer along the Lake Wobegon Trail in Holdingford, in Stearns County. Additional surveys found 18 infestations in and around the city, ranging from a few vines to a quarter-acre.
The Minnesota Department of Agriculture said the only previous known occurrence in North America was in 1958 near the Iowa State University campus in Ames, Iowa — possibly a remnant of a World War II-era research project.
"We do not know how it arrived in Minnesota," said Monika Chandler, an invasive species specialist with the MDA. The previous occurrence "was a long time ago, so it was a big surprise to find it in Holdingford. ... It certainly has us scratching our heads, as to how it got there."
State agriculture officials said Sherry Kutter, a University of Minnesota Extension Master Naturalist, first noticed the odd plant in late August. Stearns County Agricultural Inspector Bob Dunning then surveyed the infestations and notified landowners.
Dunning said it's comparable in some ways — though maybe not quite as aggressive — as kudzu in the southern U.S., climbing and covering other plants. He said once the plant first arrived in Holdingford, birds likely spread the seeds around the area.
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"We're gonna go after it," Dunning said Thursday. "A couple weeks ago, we hired a [Conservation Corps Minnesota] crew, and they came in and collected seed pods. They had a few thousand."
The seed pods were incinerated. Those efforts left many of the vines broken, so Dunning said there will be another round of work next year — herbicide and possibly some removal of the vines by hand. He estimated that the vines have been growing in the area for 3 to 5 years. (That would put the vines’ arrival well before this year’s reports of people getting “mystery” seed packets from China in the mail.)
"It's anybody's guess" how it first arrived in Minnesota, he said. "Seeds travel in funny ways. You know, it could be anything. An ATV, or somebody who was riding a bicycle somewhere else got a seed in their shoe. The odd thing is it hasn't been reported anywhere. And to me, with its aggressive nature, if there's a lot of it around, people would be noticing."
Chandler said she could not find the plant listed for sale online, and it doesn't appear to be a plant sold by garden centers. An additional mystery is how it's survived in Minnesota, because it's listed as a plant that would not do well in colder climates.
"That has not been the case; it is doing very well in central Minnesota," she said, noting the vines appear to grow well in both full sun and shade — making them more difficult to manage. Officials have not had a chance to do a formal process to assess the risk of rough potato, but Chandler said they determined the risk of the aggressive vines spreading further warranted immediate eradication efforts.
There are no vining milkweeds native to Minnesota; two other invasive types of vining milkweed — black and pale swallow-wort — have previously been found in the state.
State agriculture officials asked that anyone who sees a vining milkweed plant report it to the MDA’s Arrest the Pest line — email email@example.com, or call (888) 545-6684.