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Poison hemlock, wild parsnip flourishing – and dangerous


CINCINNATI, Ohio — The persistent rains in the Ohio Valley have played havoc on farmers who have been trying to catch up on spring planting. Now that the moisture has subsided somewhat, producers are faced with in resurgence of unwanted poison hemlock and wild parsnip in and around their fields.

Weeks of rain have spurred these unwanted plants to spread rampantly in Ohio, Indiana, Kentucky, and Michigan.

“Poison hemlock can kill you if you ingest the toxins. The toxins are in the sap and you have to get it inside of you. Wild parsnip is on the outside, so you end up with almost a second-degree sunburn,” said Joe Boggs, with Ohio State University extension.

He said the trajectory over the last 15-20 years shows the appearance of both plants has been on a constant rise. Often the two are seen growing together.

“We all know to look for poison ivy; now we need to look for these weeds, too,” Boggs explained. “Poison hemlock can kill you, while wild parsnip may make you wish you were dead.”

But what about livestock? “Of the two, poison hemlock poses a real danger to livestock,” said Michelle Arnold, extension weed scientist at the University of Kentucky. “Poison hemlock is toxic to a wide variety of animals, including cattle, sheep, goats, pigs, horses, birds, and wildlife Cattle will not eat wild parsnip but deer may feed on it, and birds and small mammals eat the seeds.

“Although cattle seldom eat hemlock, they will if no other forage is available, or it is incorporated in hay or silage. A common question is how much do cattle need to eat to kill them? Unfortunately, experts say, the answer is not clear-cut.”

Arnold said there is considerable variation in the toxic alkaloid content of the plant depending on state of growth, season, moisture, temperature, time of day, and geographical region. “Cattle have died by eating as little as 0.2 to 0.5 percent of their body weight in hemlock.”

Although this plant is often seen along roadways, abandoned lots, fence rows, and other non-cropland sites, it has expanded into grazed pasture lands and hay fields, she said.

“Symptoms of poisoning can occur within 30 minutes to two hours of ingestion depending on the animal, quantity consumed, and other ecological factors,” she added.

Poison hemlock has smooth, hollow stems with random purple spots along the lower stem that help distinguish it from other similar plants. The plant is often associated with areas that are moist, although it can also survive in dry sites.

Mature wild parsnip weeds can grow to as tall as 6 feet, while fully grown poison hemlock can be up to 10 feet tall.

Boggs said all parts of poison hemlock, one of the deadliest North American plants, should be considered dangerous, including the leaves, stems, and seeds. The roots are the most toxic part. The plant’s toxins can enter the human body through rubbing an eye or nose.

Unlike poison ivy, poison hemlock does not cause skin blistering on contact. People sometimes eat the roots of wild carrot, called Queen Anne’s lace, which bears a striking resemblance to poison hemlock.

“With wild parsnip, brushing up against the plant can cause the sap to get onto human skin,” he said. The sap invades the DNA of cells responsible for protecting one from ultraviolet radiation; go into the sun after exposure to the sap, Boggs said, and the blisters appear several days later.

“And don’t be so quick to cut down the wild parsnip,” he said. “If you do mow it, if you do cut it off, you need to make absolutely certain that you are protected against the sap. There have been reports of people using weed eaters, using clippers and things of that nature, and have gotten sap on their legs and on their arms and then ended up in the hospital.”

“With this cool, wet spring, the wild parsnip plants seem to have really enjoyed that and they’ve come up in some places a little stronger than they might normally,” said Ben Phillips, vegetable extension educator at Michigan State University.

“Wild parsnips are wilding this summer, flowering earlier and more frequently than usual. The plant is a relative of the carrot plant, and although it tastes great, it can also cause an uncomfortable rash that can last up to two days.”

The biggest warning, Boggs said, is that there are no signs of either weed slowing their growth in Ohio. “Bottom line is, they produce a lot of seed, so you can go from one plant to hundreds of plants in a very short period of time,” he noted.

Some insects will pollinate off of the flowers, but are are not impacted by the poison, nor is their nectar, which means people can keep eating honey safely.