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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

June 2000

The lovely culprit in full bloom, with bright yellow flowers on a stalk 2-5 feet high. © Robert Queen

Wild parsnip II

Itching for an update? Here are your tales of encounters with the "burning bush."

David J. Eagan

The lovely culprit in full bloom, with bright yellow flowers on a stalk 2-5 feet high.

© Robert Queen
Learning the hard way | Formula for trouble
Controlling wild parsnip | New "research" and observations
Be observant and beware | Web resources

Editor's note: Last June we printed "Burned by wild parsnip," a comprehensive look at the life history and dramatic health hazards of exposure to wild parsnip (Pastinaca sativa). We invited readers to write us via letter or e-mail to pinpoint where wild parsnip was found and describe their burning experiences with the plant. This update recounts some tales from the field and gives new health and plant control information. Thanks to all who responded.

Learning the hard way

Of 80 e-mails received, most were from Wisconsin, but some came from Minnesota, Illinois, Iowa, Indiana, Vermont and Sweden. Wild parsnip was reported in 23 Wisconsin counties; the most reports from Dane, Iowa, and Grant counties. Many correspondents noted that the weed is invading areas that were formerly parsnip-free. Conservation set-aside programs and mowing restrictions along roadsides have encouraged its spread.

Many readers reported memorable encounters with wild parsnip. You may recall that under the right conditions, this common weed can cause reddened skin and painful, blistering rashes (medically, phyto-photo-dermatitis).

Formula for trouble

Here is how wild parsnip works:

wild parsnip "sap" (photo-sensitizing chemicals in juice from green leaves, stems & seeds)

+ sensitive skin (arms, legs, torso, face, and neck – any place exposed to daylight, usually not the palms of hands. Wet skin, sweat and heat increase the effect.)

+ ultraviolet light (Present on sunny and cloudy days.)

+ time (24 to 48 hours after exposure redness, pain and blisters appear.)

= parsnip burn (Burn-like rash that, once healed, often leaves a brownish pigmentation that can last for years.)

Several wrote of burns that were serious enough to warrant hospital visits. Here is a typical tale: "Last year we did a lot of work outside in the hot sun. One day I noticed two or three nickel-sized blisters on the backs of my legs, which healed after a short time, though I still have faint, dark spots where they were."

Another reader made an interesting observation. The leader of a line of hikers – through a parsnip-infested field – was untouched, but as second in line, our writer suffered severe burns. Others were affected, though severity was "successively less" down the line.

Respondents confirmed that wild parsnip's rash often is misdiagnosed as poison ivy. Several mentioned that the article cleared long-standing mysteries. "After reading your article," someone wrote, "I (now) realize that I was burned by wild parsnip several years ago. I got huge blisters on my hands while on a canoe trip. I thought it was bad sunburn but my doctor said it was poison ivy. Another doctor thought it looked more like a burn but didn't know where the burn came from."

Keep in mind that nobody is "immune" to wild parsnip. Some think that because they never have been burned – after close contact with the plant – they are safe. Getting the right combination of juice, sun and time, however, usually proves the point. One such burn-free doubter joined me in a parsnip-pulling party last July. He wore long pants but only a short-sleeved shirt, insisting he was immune. A few days later he e-mailed: "My arms are resplendent with blisters and pustules – but they don't hurt or itch. It's good to know that I'm normal."

Controlling wild parsnip
If you discover an invasion early, concentrate on preventing plants from flowering and making seeds. For established populations, you will need to cut, pull or treat plants with herbicides for several years in a row. Visit the DNR invasive-species website, or contact your extension agent for advice. don't forget to wear protective clothing!

Cutting the root – With a sharp blade or shovel, cut the root an inch or two below ground level and lift plants out.

Pulling plants – When in flower and after a rain, mature plants can be pulled easily from the ground. Pull before seeds ripen. Roots can be loosened with a trowel or shovel.

Mowing – Large areas can be mowed, but wait until flowering begins. Flower stalks may resprout, so repeated mowing is often enough to prevent seed formation.

Chemical control – Use herbicides sparingly. Spot-spray ear.

New "research" and observations

Wild parsnip is not the only phototoxic plant found in Wisconsin. Cow parsnip (Heracleum lanatum), a larger, native relative, produced some strong burns when tested on skin. And two garden plants – rue (Ruta sp.) and gas-plant (Dictamnus sp.) – were reported by readers as causing sun-induced burns.

I conducted experiments to better understand the burn reaction. In one test, I touched a freshly-cut parsnip leaf stem to my skin – a spot on each arm – then covered one spot with an adhesive bandage. Both arms then received much sunlight. Forty-eight hours later, the uncovered spot was red and became blistered, while the covered spot stayed normal. In another test, again on my arms, wild parsnip juice was applied in several places at sunset, but wasn't exposed to sunlight until the next day, resulting in faint redness or none at all. The sensitizing effects seem to diminish over a relatively short period. According to dermatology textbooks, the skin's sensitivity to ultraviolet light peaks 30-120 minutes after contact.

A few readers mentioned washing as a method of preventing burns. In my experience, washing might help but only if done immediately after contact. Because the active chemicals are lipid-soluble they are absorbed quickly into the skin. In a test, I applied two identical spots of juice indoors, at mid-morning. After 10 minutes I washed one spot thoroughly with soap and water, and washed the second after 30 minutes. I went outdoors around noon, making sure the spots were exposed to full sunlight. Both turned red in 24 hours and after 48 hours a blister formed on the 30-minute spot. Two days after that, the 10-minute spot also blistered.

Two readers noted that despite wearing protective clothing, they still got parsnip burns. One wrote, "Even when wearing gloves, old socks as wrist guards, long pants and long-sleeved shirts, I still had parsnip juice seep through onto my hands and wrists, leaving those telltale blisters."

This happened to me last summer on a steamy day, resulting in mild burns on my arms and sides. While pulling parsnip, juice had soaked into my clothing, mixed with perspiration and got onto my skin. As soon as I was out of the danger zone, I peeled off my sweat-soaked clothes and put shorts back on, exposing my bare, sensitized skin. Lesson learned: next time, I know to change my clothes out of the sunlight and either put on dry, sun-proof clothing or stay indoors. Alternatively, do parsnip control in the early evening and quit after sundown.

Be observant and beware

This time of year, wild parsnip is green, mean and more widespread than ever. Many who responded to last year's query said they often teach about the plant's hazards and help spread the warning to others. One noted, "After my own experiences, I avoid it and educate about wild parsnip whenever possible." I invite you to do the same. With some effort, Wisconsin residents may someday be as familiar with wild parsnip as they are with the dandelion – though I hope it will never be as abundant.

Web resources

By avocation, David Eagan is a naturalist who battles wild parsnip on an Iowa County prairie remnant. (More parsnip stories are invited – e-mail David Eagan or write P.O. Box 3020, Madison, WI 53704.)