Dr. Leonard Perry, University of Vermont Extension Professor
(Wild Parsnip, photo courtesy it.wikipedia.org)
If you live in all but the most southern parts of the Southeast U.S., you may be seeing a tall yellow “wildflower” 4 to 6 feet tall about now all along roads (and if like me throughout your garden beds too)– somewhat attractive in mass and first glance. This is the wild parsnip (Pastinaca sativa), the escaped and naturalized form of the parsnip that was introduced as a root crop. It is similar to the cow parsnip or giant hogweed which is in a different genus (Heracleum) and has white flowers instead. Both have flowers in forked umbrella arrangement (umbels) similar to Queen Anne’s lace and other members of the carrot family. If growing in a wet area, has purple mottling on stems, white flowers, is about 10feet tall, and has a “mousy” odor not a “parsnip” odor, it may be the quite poisonous related water hemlock (Conium).
What makes wild parsnip so bad (yes it has edible roots), is that it is VERY seed invasive. A few years ago I saw a plant or two in our field, then only a few years later it is everywhere and virtually impossible to get all the plants. The seeds are quite viable, will germinate among tall grasses, and kill out much other vegetation.
Beauty and the Burn (to quote the NY DEC magazine article title)– Another bad feature is that the sap, when it gets on the skin in sunlight, causes rashes and blistering for several hours in many people– a malady termed phytophotodermititis. So use long sleeves and gloves when pulling it out or working with or around it. It can cause similar symptoms in light-skinned cattle, livestock and horses and, if ingested either fresh or dried in hay, can result in severe sunburning. (The toxic furanocoumarin, specifically psoralen, in the sap causes injury when exposed to the UV rays in sunlight.) So as this invasive spreads through pastures, it is important that farmers make sure their hay doesn’t contain it. And if livestock such as goats graze, make sure they don’t eat it.
As I write this in Vermont the end of June, flowers are peaking, and over the next 3 weeks will produce viable seeds. This period is the best time to deal with it, as 1. it is quite visible and easy to find, and 2. cutting off at the base or preferably just below the ground level (I used long-handled loppers or simply a spade) it is less likely to resprout then. Earlier in the season it merely resprouts, as it does with burning. Chemicals (such as those with glyphosate) can be used too, applying according to label directions to the basal portions once the top is cut off. Use caution as such herbicides kill other surrounding vegetation they touch as well. Or, you can merely cut off the tops before they go to seed, just keeping in mind they may then reflower later so need attention then too. If a large infested area without desirable ornamentals or other plants, you can merely mow the whole area such as with a brush cutter or weeder (with heavy duty grass blade).
This perennial is called “monocarpic”, meaning it takes one of more years to develop a basal rosette of leaves, then flowers, and once seeds are produced it dies. So keeping the seeds from forming and spreading will eventually provide the best control. Act now, do your part to keep this invader out of gardens and off invasive plant lists (many of which it surprisingly isn’t on, yet, especially in New England). Much of the online information is from Midwestern states, such as the MN DOT (http://www.dot.state.mn.us/adopt/files/WildParsnip%20IIII_1.pdf).