Poison parsnip invasion spreading

ADDISON COUNTY — Driving south down Route 30 one summer morning, Addison County Forester Chris Olson came across an out-of-state car parked along the side of the road. He drew closer and noticed a woman picking wildflowers that looked just like Queen Anne’s lace, only yellow in color.
“As I whipped by I saw what she had in her hand,” said Olson.
So he spun around, pulled up behind her, got out of his car and approached the woman holding a bouquet of the yellow flowers.
“Don’t be alarmed,” he told the woman. “I’m the state of Vermont’s County Forester, and the reason that I’m stopping is because that plant that you’re holding in your hand is poison parsnip, and it creates a sun-activated chemical burn.”
She opened her hand and dropped the flowers.
“What I recommend is that as soon as you can, you go and wash your hands because it’s a light activated chemical that will create serious blisters,” said Olson, who has felt the blistering wrath of poison parsnip every summer for the last ten years.
Click here to read about Giant Hogweed, another invasive plant species.
This invasive species is by now no stranger to Addison County residents, who should recognize its yellow flowers lining many local roads. When the sap from the inside of the stems or leaves of the wild parsnip gets on skin, exposure to ultra violet light can cause a burn. It’s not like poison ivy, which has oil on its leaves that stimulates a reaction when it touches the skin.
What might come as a surprise is that this hostile variety of parsnip is a sibling to the one found in domestic gardens.
“The same active compounds are present in the parsnip that you find along the road as are in your gardens,” said Tim Schmalz, state plant pathologist for the Agency of Agriculture. “They occur in much lower concentrations … but they’re there, and we encourage people to be careful when dealing with the tops of their parsnips in their gardens, just as we would the folks dealing with it along the highway.”
According to Schmalz, these same compounds can be found in carrots, cilantro, fennel, Queen Anne’s lace, hemlock, celery, dill and many other plants belonging to the larger biological family (known as Apiaceae).
“You can eat the parsnips that are growing along the side of the road, but you probably won’t like them,” said Schmalz. “It’s just the species parsnip, but probably not the same variety or cultivar that you’re accustomed to eating.”
Many local experts, like Olson, note that wild parsnip seems to be rapidly taking over.
“My impression is that the population has exploded over the past ten years. I think it’s been expanding at an exponential rate,” said Olson. “I understand that the Pringle Herbarium at UVM (University of Vermont) has record of this being in Vermont for a long time. So it’s not new to Vermont in the last 15 years, but something has caused it to be more prevalent.”
The reasons for the increase appear to stem from the relationship of the plant to human behavior. Parsnip is a biennial, meaning that it takes two years to seed and then dies. But its seeds can lie in the ground and remain viable for as long as four years.
Tim Parsons, horticulturalist and arborist for Middlebury College, thinks that the plant’s rapid expansion along roadsides might be due to mowing schedules.
“The way to think about poison parsnip … is come hell or high water it wants to bloom that second year,” he said. “If you mow the plant before it blooms it’s got a large enough tap root that it can send more shoots out. So therefore you cut off one bloom and you’ve got four or five (more) blooms. (People) seem to be mowing before the plants bloom, so they actually seem to be producing more blooms.”
At the same time, Parsons finds it difficult to imagine waiting until July or August to mow the roadsides.
Another theory proposed by Olson is that underused farmland in Addison County has given the wild parsnip, which thrives in well-lit swathes of land, a chance to proliferate.
“I think generally there might be more fallow agricultural land due to the industry being in the state that it’s in, which has allowed the problem to perpetuate,” said Olson. “I sort of wonder if there’s some change in temperature, moisture, heating degree days, whatever the metric would be – CO2 levels or something – that promotes its growth or allows it to expand faster than plants that have otherwise competed with it. But I don’t know the reason behind this.”
None of the plant experts who spoke with the Independent were able to identify a salient cause behind this invasive species’ expansion, and there doesn’t seem to be a government or non-governmental organization that has been able to quantitatively chart the plant’s proliferation.
There are, however, means to eliminate wild parsnip.
One way to control it, Schmalz said, is by waiting to cut the plant until right before its seeds are able to germinate. Only in the second year will the plant bloom.
Therefore, the plant can’t be cut too early because doing so will create more blooms, and the plant can’t be cut too late because doing so will send fully developed seeds into the ground, where they can sprout for up to four years.
“It’s easily managed prior to seed set if you cut it before the seeds become viable … you’ve got to time (cutting) to your infestation,” said Schmalz. “I would guess in Middlebury area you’ll probably do your best cutting in mid-July … but there’s no hard-and-fast rule for everywhere.”
Schmalz and Parsons mentioned that certain herbicides might also work, and Parsons believes that the most effective method is to overcrowd the parsnip with another crop and choke it out.
In order to avoid parsnip’s painful burns, which left Parsons with scars for years after a previous run-in, Schmalz provides a remedy.
He recommends wearing long pants, sleeves and eyeglasses, and dealing with the plant early in the morning or on a rainy day when sun exposure is reduced. He said to wash immediately after and not to weed-whack in the middle of the day.
“Be aware of it and how to avoid it, and you can avoid being burned by these plants,” Schmalz said. “I work with (parsnip) a lot and I’ve never had a problem with it, and I’m not out there in a bee keeper’s suit.”
For more information on dealing with poison parsnip, Vermont Plant Pathologist Tim Schmalz is available at 802-241-3544.
Reporter Andrew Stein is at [email protected]

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