The dark side of the veggie world
- Laurie Sidle, OSU Extension Wayne Co.
- June 29, 2021
- 1062
Most of us would benefit greatly from eating more fresh vegetables and fruits. While it can be a challenge to get children (and some adults) to eat these healthy foods, some of our vegetables’ “cousins” are legitimately troublesome.
Poison hemlock, wild parsnip, cow parsnip, and giant hogweed are four plants in the Apiaceae family of plants which also includes carrots, parsley, celery, and (cultivated) parsnips. Being in the same family, these plants share several characteristics. They have umbrella shaped flower clusters that are usually white. Their leaves resemble anything from carrot tops to giant celery leaves.
These plants typically follow a biennial life cycle. In the first year, the seed forms a low-growing rosette in the spring and stays fairly small while storing nutrients in a large taproot (like a carrot). In the following year, these plants rapidly increase in size and produce a stalk with flowers.
It is extremely rare to find cow parsnip or giant hogweed in or around Wayne County, Ohio. Both of those plants are poisonous and should not be touched. Suspected sightings of these should be reported for confirmation to the ODA by calling 1-800-282-1955.
Because those two plants are so rare, this article will focus on poison hemlock and wild parsnip.
Poison hemlock is a very large plant in its second year, often growing over 6 feet tall. It has hollow stems with purple spots and clusters of white flowers that begin blooming in May. The leaves most closely resemble carrot tops. All parts of the plant are poisonous as they contain alkaloids. Ingesting even small amounts of this plant can be lethal to both people and livestock. While touching poison hemlock may not cause skin irritation or blistering, it is not advised to handle it during control and protective gear and caution should be used as many of its look-a-likes can cause severe skin, eye, and other bodily harm.
Wild parsnip is also a large plant, but usually does not reach heights of more than 5 feet. Unlike most plants in this family, it has yellow flower clusters instead of white. Its stem has pronounced ridges and lacks any purple spots. The leaves of this plant closely resemble celery leaves. Wild parsnip sap contains psoralen, a chemical that causes skin to become extremely sensitive to UV radiation from sunlight, which causes a rash and/or severe blistering. Breaking, mowing, or trimming wild parsnip stems or leaves releases the sap, increasing the likelihood of it coming in contact with skin. This is the same chemical found in giant hogweed and cow parsnip.
Queen Anne’s Lace, also called wild carrot, is another plant in this family. It is much smaller than the two harmful weeds described above and blooms later in the summer. The flowers are white, and the stems are covered in fine hairs. There have been some reports of skin irritation from handling this plant though it is not usually considered dangerous or poisonous to people or livestock.
Control of both poison hemlock and wild parsnip is most effective when the plants are small, prior to flowering in their second year. This can be challenging as the plants are not highly noticeable until they reach several feet and produce flowers.
Mechanical control of these plants can be challenging from a safety and efficacy standpoint. Mowing, cutting, or digging wild parsnip can be a safety hazard as these methods require close proximity and sap exposure is greatly increased. Mowing poison hemlock is most effective when the plant has just started to bolt as the young, low-growing rosette stage will likely be beneath the cutting height.
The most effective chemical control products include 2,4-D + triclopyr (Crossbow), Dicamba, and glyphosate (Roundup). These are most effective when the plants are small. 2,4-D, triclopyr, and dicamba are selective herbicides and will not kill grasses. Glyphosate is non-selective and will kill nearly all plants when applied correctly. Always follow label instructions when applying herbicides including rate, timing, and location.
Once these plants have formed flowers, viable seed production follows closely. Thus, chemical and mechanical control after flowering may not prevent new plants from emerging the following year.
Wild parsnip and poison hemlock are on the Ohio Prohibited Noxious Weed List. Plants on this list must be removed and destroyed by law. Landowners are responsible to control and remove noxious weeds on their property. Proper legal channels to resolve issues typically involve local township authorities. An OSU law bulletin is available online or by request for more information on noxious weed control.
Matthew Nussbaum is an OSU Extension agriculture and natural resources program assistant and may be reached at 330-264-8722.