Non-Native Invasive Species

Wild parsnip

Pastinaca sativa

Wild parsnip

Wild parsnip
Photo: Ohio State Weed Lab Archive, Ohio State University, Bugwood.org

Property owners and wildland managers know how laborious and time-consuming it can be to control invasive plants, whether it's grubbing out honeysuckle shrubs, struggling with dense thickets of barberry, or hand-pulling garlic mustard plantlets. One invasive plant, however, is not only fast-spreading and difficult to eradicate, it's also occasionally poisonous to people and to some animals. Known regionally as poison parsnip and elsewhere as wild parsnip, this yellow-flowering relative of the cultivated root vegetable is nearly ubiquitous along our roadsides.

Wild parsnip

Wild parsnip
Photo: Ohio State Weed Lab Archive, Ohio State University, Bugwood.org

Wild parsnip is usually a biennial, dying after it flowers in its second growing season. The first year it is a well-behaved "rosette" - a low, round, cluster of leaves. In year two, plants grow to three feet or more. Many-parted celery-like leaves are carried on stout stems, most of which, right now in early summer, terminate in flat-topped clusters of tiny yellow-green flowers. Seeds follow in mid-summer, and seed production is enormous.

Prodigious seed set is a big part of the reason wild parsnip has become so common along roadsides in Vermont, where mowing crews unintentionally spread the seeds along right-of-ways and from there into fields, pastures, and even sunny wetlands. Mowing also seems to reduce competition from more desirable plants. Some studies of wild parsnip invasions of Midwestern prairies indicate that benign neglect is the best management strategy: if left uncut, it is usually fairly quickly outcompeted by other species.

Wild parsnip

Wild parsnip
Photo: John Cardina, Ohio State University, Bugwood.org

But if you haven't the time to let nature take its course in your own yard, the most reliable control method is using a shovel to slice off the part of the plant just below the ground. (That removes the growing tip that spurs rosette formation.) And when you do so, dress for the occasion - which is to say wear long pants, long sleeves, and gloves. Wild parsnip "juice" contains compounds which, when splashed on the skin and then exposed to ultraviolet light, causes painful blisters, sometimes very large ones, on some people. (This phenomenon is called "phytophotodermatitis" - "phyto" for "plant" and "photo" for "light.") The blistering occurs hours, even a day or more, after exposure to wild parsnip sap. People who've suffered the ailment say it feels like an awful sunburn. Short-haired animals can also be harmed by wild parsnip sap.

Not insects ingesting it. Careful observers might notice on many or most plants in a group that a caterpillar has come to visit, and eat. Parsnip webworm is very common, but researchers think not common or destructive enough to offer control of this pretty, but noxious, weed.