Poison Hemlock Needs To Be Watched

OMAHA (DTN) -- As the name implies, poison hemlock is toxic to both animals and humans. The plant can pretty much grow anywhere, but is often found in pastures and hay fields, especially in areas that tend to be damp.

How much livestock would have to eat to kill them is not clear cut. However, there are different control methods, which can be utilized in pastures and hay fields, according to extension specialists.

LIVESTOCK CAN BE POISONED

In a February 2024 article titled "Be Aware of Poison Hemlock Dangers to Livestock", University of Kentucky Extension agent for Carter County Rebecca Konopka wrote people are usually poisoned when they eat the plant, mistaking it for wild parsley, wild carrot or wild anise. See that here: https://carter.ca.uky.edu/…. Cattle will seldom eat poison hemlock but will if there is no other forage available or if it is in hay or silage.

The plants are often seen along roadways, abandoned lots, fencerows and other non-cropland. Konopka wrote in recent years, the plants have expanded into grazed pasture lands and hay fields.

"Poison hemlock is classified as a biennial that reproduces only by seed," Konopka wrote. "It is capable, however, of completing its lifecycle as a winter annual in Kentucky if it germinates in the fall."

A common question Konopka receives is how much do cattle need to eat to kill them. This question is not clear cut with considerable variation in the toxic content of the plant depending on stage of growth, season, moisture, temperature, time of day and even geographical region, she said.

POISON AFFECTS LIVESTOCK TWO WAYS

The plant's poison has two major effects on animals. One would be rapid, sometimes fatal effects on the nervous system; the other is birth defects in offspring. "Cattle have died by eating as little as 0.2-0.5 percent of their body weight in green hemlock," Konopka wrote.

Symptoms of poisoning can occur within 30 minutes to two hours of ingestion depending on the animal, quantity consumed and other ecologic factors. Signs of acute poisoning include nervousness, trembling, muscle weakness, incoordination, salivation or slobbering.

Although acute disease is the primary concern, an equally serious problem would be subacute intoxication of pregnant livestock, which could cause deformed bones or joints in calves or pigs.

For this to happen, the animals must eat the plant for an extended period during the first trimester of pregnancy. The susceptible stage of gestation for maternal exposure for cattle is from 50 to 75 days for skeletal defects to occur, such as crooked legs, deformed necks and spines, she wrote.

"Public health is a concern when dealing with poisoned animals because of the possibility of alkaloid residues in meat," Konopka wrote. "Elimination of plant toxicants through the milk is a minor route of excretion but may be important when consumed by a calf or human."

DIFFERENT METHODS TO CONTROL HEMLOCK

According to the article "Haying and Cattle Grazing Areas with Hemlock" by the University of Nebraska-Lincoln (UNL) Extension from August 2024, there are two ways to control the deadly plants. See that here: https://beef.unl.edu/…. Producers can attempt to control the weed by physical or chemical methods.

Physical removal of plants can be effective if it is a steady effort and is applied over time. Personal protective equipment (PPE) should be used, as hemlock is poisonous for humans through skin contact or ingestion.

For larger infestations, UNL suggested chemical control be used via a broadleaf herbicide. 2,4-D plus Dicamba is an example and spraying in the spring and the fall are the most effective application times.

"Since water hemlock grows near water sources, herbicides will need to be labeled for use in water area and should be done with caution," the UNL report said. "Read the herbicide label."

It is also important to know if physical removal is utilized, you should never burn the plants. The smoke from burning hemlock is highly toxic to humans if inhaled, according to the UNL article.

ERADICATE PLANTS TO PROTECT LIVESTOCK

If you notice that your grazing or hay lands contain hemlock plants, strongly consider eradicating these plants, according to UNL. It is also recommended fencing livestock out of patches until the hemlock can be killed and removed.

Livestock producers should also try to avoid incorporating hemlock into hay bales. If you suspect that hemlock may be in hay that you plan to feed, strongly consider feeding it unprocessed and in sufficient quality to allow livestock to sort out the less palatable hemlock.

"However, animals may still be at risk for poisoning if the hemlock is consumed by the animal," the UNL report said.

There are several resources to help you identify poison or water hemlock, as there are other benign plants that look similar.

This link provides pictures and information about both hemlocks: https://extensionpubs.unl.edu/… .

DTN Crop Technology Editor Pamela Smith recently wrote a blog about poison hemlock and wild parsnip. The post can be found here: https://www.dtnpf.com/….

Russ Quinn can be reached at Russ.Quinn@dtn.com

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