Invasive hemlock species discovered in Kent, Sussex County

By Mike Finney
Posted 7/7/21

DOVER — Todd Davis, environmental program manager for the Delaware Department of Agriculture’s Noxious Weed and Seed Lab, warns residents that it is not a good idea right now to cut …

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Invasive hemlock species discovered in Kent, Sussex County


DOVER — Todd Davis, environmental program manager for the Delaware Department of Agriculture’s Noxious Weed and Seed Lab, warns residents that it is not a good idea right now to cut blooming flowers near stormwater ponds in housing developments, ditches or alongside the road.

That’s because environmental scientists have confirmed the presence of poison hemlock (Conicum maculatum) and spotted water hemlock (Cicuta maculata) in both Kent and Sussex County. All parts of the plants — leaves, stems, flowers, and roots — are poisonous to humans and animals.

Both hemlocks are in bloom from June through August. As members of the wild carrot family, both plants have small white flowers in umbrella-like groupings.

“It’s a little bigger than we thought,” said Mr. Davis, of the hemlocks, which were first spotted in Sussex County. “We’re finding it in other areas. We found it in Kent County (Tuesday). It’s kind of like now is the time of year that it flowers and now that we’ve seen it and are comfortable in identifying it it’s easier to see out there, mostly in ditches and sides of roads.

“A couple of the sites that we’ve got in Sussex County are in developments where they’ve got a new stormwater pond – within the last five years maybe. There’s hundreds of stormwater ponds down there. Some folks are letting us know it’s out there and they brought it to our attention.”

Mr. Davis said individuals may mistake the hemlock plants for wild carrot, commonly called Queen Anne’s lace, or wild parsnip or wild celery. People who like to forage for natural foods or cut wildflowers are advised to avoid wild carrot-looking plants to prevent the possibility of being poisoned.

Both the poison hemlock and spotted water hemlock were found in wetland areas in Kent and Sussex County. Poison hemlock is also known to grow in ditches, meadows, pastures and the edges of cultivated fields.

“It’s not really widespread, but the more we look the more we find,” Mr. Davis said. “It’s hard to put a definition on it. The issue we find is a lot of times when we find (hemlock) it appears that someone has been there already and cut off some of the seed heads for a flower arrangement.

“They think it’s a wild carrot and it’s very similar. The more you read into this it talks about different people have different reactions to things. It even says to not cut it because you can breathe in some of the particles that creates in the air.”

He added, “But it is highly toxic. When you look it up, you will find that the spotted water hemlock is the most poisonous plant in America. It’s nothing new. It’s just out there a little more this year.”

ID’ing the hemlocks

Poison hemlock is an invasive biennial that grows from six to eight feet tall. The stems are hairless and have purple blotches.

The plant emits an odor, but people should not crush any part of the plant to smell it because toxic alkaline oils can be released, poisoning the person. Leaves are alternate, dark glossy green, fern-like, triangular, lacy with veins running through the tips of the leaf serrations.

Native to Europe, northern Africa, and western Asia, poison hemlock was introduced into the United States in the 1800s as an ornamental garden plant.

Spotted water hemlock is a native plant that grows up to six feet tall. The stems can vary in color from solid green or purple to green with purple spots or stripes. The leaves are lacy and fern-like, with veins ending at the base of the notch of the leaf edge.

If residents suspect they have found either of these plants, Mr. Davis requests that they take a picture and email it to for identification.

Residents should not try to eradicate these plants themselves. Residents should find a licensed aquatic pest control company  to treat for poison hemlock or spotted water hemlock.

“I just know that hemlock can cause a severe skin irritation to humans and is toxic to livestock if ingested,” said Megan Pleasanton, extension educator for the Small Farms Program at Delaware State University. “It is commonly mistaken as Queen Anne’s Lace or Wild Carrot that also tend to grow in meadows or along ditch banks. I encourage folks to wear gloves, long sleeves, and pay special attention while pulling weeds.”

Mr. Davis said that finding hemlock in Delaware is nothing new.

“We saw it three years ago but that was on a DelDOT site, so it was mowed and sprayed,” he said. “We didn’t see it last year, but it’s there this year. You never know whether the winter makes some of the seeds viable. Some seeds lay there dormant, and the winter weather is what makes them break out.

“We’ve read that some birds can move the seeds even though they’re poisonous, so we don’t know if that’s the case with the stormwater ponds because (the hemlocks are found) all the way around the perimeter. It doesn’t seem to grow right in the standing water, it grows on the land, but closest to the water.”

The dangers of hemlock exposure

Mr. Davis pointed out that people have different reactions when they come in contact with hemlock.

Depending on the exposure — direct contact, ingestion, and inhalation — signs and symptoms of poisoning by spotted water hemlock and poison hemlock in humans can appear as soon as 15 minutes to hours and can include nausea, vomiting, diarrhea, stomach pain, irregular heartbeat, dilation of the pupils, respiratory distress, muscle damage, renal failure, and central nervous system involvement causing seizures, with potential for death.

If a person may have ingested either of these plants or cut one of the plants inhaling the toxic particles, call the Poison Control Center at 1-800-222-1222 or 911.

Mr. Davis said Pennsylvania and Maryland scientists have both also discovered spotted hemlock growing this summer.

The identification and eradication of the poisonous plants are crucial in meadows and fields where livestock and horses graze.

If any part of the plant is ingested, toxicity can occur in animals. All classes of livestock are susceptible to poison hemlock. Ingestion of the plant may lead to death within just 2-3 hours, depending on the amount consumed.

Fresh leaves of poison hemlock are unpalatable to animals, so livestock and horses seldom eat hemlock if other feed is available.

Clinical signs in livestock usually begin within 30-60 minutes after ingestion. There is no antidote. When animals ingest the plant, the toxin affects nerve impulse transmission to the muscles, and animals die due to respiratory failure. Animals often will be found dead before the illness is determined.

“We deal with invasive plants all the time, but this is just one that’s come to light this year and it seems just a little more prevalent and with the toxicity of it we thought that we should get it out there,” Mr. Davis said.