Watch out for poisonous plants in Ohio

poison hemlock flower
Poison hemlock is one of the most toxic plants in the area. Infestations of this plant and wild parsnip are flourishing in southern Ohio. (Photo by Joe Boggs, OSU Extension)

SALEM, Ohio — Poison hemlock and wild parsnip infestations are thriving in southern Ohio this year, after increasing for the last 15 years, according to Ohio State University Extension assistant professor Joe Boggs.

It may be too late to manage infestations in southern Ohio, but the central and northern regions may still have time.

Identifying the plants

invasive weed field guide
Poison hemlock and wild parsnip infestations are flourishing in southern Ohio. It is important to learn how to identify and manage these poisonous plants.

In a blog for Buckeye Yard & Garden onLine, Boggs and commercial horticulture educator, Erik Draper, said poison hemlock and wild parsnip look similar, not only to each other, but also to some innocuous plants.

The plants are often found growing together. Boggs said there are several ways to tell them apart. Poison hemlock has white flowers in an umbrella shape, while wild parsnip has yellow, flat-topped flowers.

Poison hemlock has purple mottled stems, while wild parsnips have stems with deep grooves and no mottling.

According to Ohio Perennial and Biennial Weed Guide, poison hemlock can grow nearly to 10 feet, while wild parsnips only reach about 5 feet.

Innocuous species

Poison hemlock can be mistaken for wild carrot, or Queen Anne’s lace. Boggs said while wild carrot has white flowers, they are flat-topped, not umbrella-shaped like poison hemlock flowers.

Garden angelica, which has a deep purple stem, has also been mistaken for poison hemlock. Boggs said garden angelica has a solid purple stem, not mottled purple like poison hemlock.

It can be difficult to recognize plants without seeing them in person.

“Use the pictures to find the plant, and then identify the plant and see what it looks like in real life,” Boggs said. After identifying a plant in-person, most people will have an easier time recognizing it without the pictures in the future.

Managing infestations

Boggs recommended using selective herbicides to manage both plants. Non-selective herbicides will also kill other plants and create room for poison hemlock or wild parsnip seeds left behind to germinate.

He said people can also try cutting the plants down, but advised caution.

“It doesn’t take a lot to produce a reaction,” he said about wild parsnips.

Similarly, poison hemlock is one of the most toxic plants in the area and small amounts can be very harmful. While it must be ingested or pass through a mucous membrane to do harm, people should be cautious when cutting poison hemlock.

Effective management

If a plant is already in full flower and pollinated, it could still produce seeds that bring the infestation back next year. Boggs suggested marking where infestations are present and using selective herbicides on those areas early in the spring next year.

“A lot of people focus their weed management a little too late” for these plants, Boggs said, noting both are very early season plants.

Symptoms of poisoning

Poison hemlock can kill. It can cause respiratory failure and death in mammals, and all parts of the plant are dangerous.

Wild parsnip is dangerous because of the sap. The sap damages skin cells that protect skin from the long-wave ultraviolet radiation in sunlight. So, when skin affected by the sap comes into contact with long-wave ultraviolet radiation from the sun, it blisters.

“The blistering is very similar to a second-degree burn,” Boggs said.

Because symptoms do not appear for around 24 hours after exposure, many people do not realize the symptoms they experience come from wild parsnips.

The best way to avoid poisoning is to avoid handling these plants. Boggs said anyone who does come into contact with either plant should seek medical attention.


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