Cow parsnip or the toxic hogweed (Heracleum)

submitted by Fred Schueler for Fragile Inheritance Natural History
In the late spring of recent years, there’s always a lot of public fuss about “Wild” or “Poison” Parsnips, and the threat they pose to anyone who comes into contact with them. In the past couple of years, counties and the city of Ottawa have been spraying herbicides to kill roadside Parsnips and other broad-leaved “weeds,” and issuing warnings about the frightening danger Parsnips pose.
It seems that, over the past 30 years, these escaped descendants of the garden vegetable have become more widespread in Ontario. In many summers, the roadsides of eastern Ontario are overrun with their yellow blooms, though there’s a sudden cut-off along many roads when they enter the Shield bedrock of the Frontenac Axis. The sap of Parsnips will cause what is termed “phyto-photo-dermatitis” if it gets on tender skin which is subsequently exposed to the sun. It’s the combination of sap+sun that’s the problem, and some people seem to be more sensitive than others. The rash can be quite painful, although not itchy, with the skin lumpy from rash and blisters, like a very severe case of poison ivy. These blisters are much longer-lasting than those of poison ivy, and the scars last for years.
It’s likely that the combined increase in feral populations of Parsnip, the modern preference for running about half-clad, and the recent prevalence of vegetation-shredding machinery has increased the rate at which sensitive skin simultaneously comes in contact with Parsnip sap and sunlight.
I’ve only been nailed by Parsnip sap once, on the inside of my elbow, when I was cutting plants for chicken feed. The blister lasted for a couple of months, and the scar for a few years. The sap of many other plants in this family, Apiaceae or Umbellifers, including Carrots, can also cause phyto-photo-dermatitis. Parsnip flowers are a wonderful nectar source for flies and other small insects, and Parsnips are a host plant for gorgeous Black Swallowtail caterpillars, which mature as one of our handsomest butterflies.
When it’s necessary to remove Parsnips from a small area, the plants can be pulled up in the evening, or on an overcast day, while wearing clothes. I’ve cleaned up neglected gardens which were yellow with Parsnip bloom by working after dusk, wearing gloves, and piling the pulled plants so the seed heads are off the ground. If the seed can’t fall down onto bare soil it won’t (in my experience) germinate.
Extensive stands can be repeatedly mowed, when the Sun isn’t out (and washing up afterwards): mowing only once will just result in the sprouting of smaller flowerstalks. Any control needs to continue for a few years, because there will be a “seed bank” in the soil which will continue to germinate plants until it is exhausted.
One Parsnip plant isn’t a threat, as one poison ivy plant might be, because the dermatitis isn’t contact dermatitis, it’s due to the sap from broken stems and leaves, and the threat comes in shredding or hacking through large stands and getting smeared or sprayed with the sap.
The tastiest way to diminish any threat from the sap of the tall second-year plants is to dig and eat the roots of the first-year plants after frost. These are just as edible as their domesticated cousins, though the daughter’s infant name for them – “Rattails” – suggests their average size, and it’s important not to eat any of the related poisonous species, such as Water Hemlock (an Internet search, or any edible plant guide will give the identifying characters).
As with domestic Parsnips, the roots are sweeter after frost and they are also edible in the spring, though a little softer and more fibrous than in the fall. Even in late May, as the stalks are beginning to elongate, the roots can be cooked up, though at this season they’re rugged with tough fibres.
Naturalists are concerned that publicity about Parsnips focuses on exaggerated accounts of the phyto-photo-dermatitis, without referencing the use of the roots for food, and that control programmes for Parsnip ignore the question of how to encourage Webworms to provide some degree of natural control.

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