Poisonous plants are a major cause of economic loss to the livestock industry. They can cause death, abortion, poor production, and birth defects, to name a few. Each year these plants adversely affect 3%–5% of the cattle, sheep, and horses that graze Western ranges.
Two such plants common to Oregon are poison hemlock and Western waterhemlock. Ingestion of either by humans or livestock typically results in death.
The deadly properties of hemlock have been known for centuries. Socrates is the most famous victim of these properties; he was forced to drink a toxic potion made from hemlock in 329 B.C. Native Americans also used the juice of the hemlock plant to poison the tips of their arrows.
In the past, the roots of poison hemlock have been mistaken for wild parsnips and eaten by people. A Tacoma, Washington, woman apparently put hemlock in a salad she ate and died. Stories abound regarding pets dying from encounters with it in fields, or children making whistles or snorkels from the hollow stems of these plants and becoming ill and succumbing to the toxic alkaloids present in all parts of the plant.
Let's look at the differences between these deadly plants and include some strategies for eliminating them from your property.
Poison hemlock, Conium maculatum
Poison hemlock, also called poison parsley, is a member of the plant family Apiaceae. Other members of this plant family include carrots, celery, and parsnip. Like other members in this plant family, poison hemlock flowers have white, umbrella-shaped clusters in addition to the fernlike appearance of the leaves. This why people over the years have mistaken poison hemlock for wild carrot, wild parsnip, or wild parsley.
This plant is distributed throughout North America and was brought here by Europeans sometime in the 1800s. Poison hemlock quickly escaped their gardens and now infests roadsides, creeks, irrigation ditches, cultivated fields, and pastures. Poison hemlock typically grows in wet soils, but on occasion can tolerate semi-dry soils. It has been found in gardens, in pastures, and in crops.
Poison hemlock grows into a rosette the first year but does not flower until its second year. Each flower develops into a green, deeply ridged fruit that contains several seeds. After maturity, the fruit turns grayish brown. It is a biennial, or sometimes in favorable conditions it may be a perennial, growing 3–8 feet tall and occasionally reaching 10–12 feet.
During the first year of growth, poison hemlock forms a large rosette and usually remains in the vegetative stage. During the second year, it produces tall stems and then flowers. The large, dried stems have been known to remain toxic for up to three years.
Poison hemlock can be differentiated from a carrot or parsnip plant by the profuse number of purple spots on the stem. Leaves are also smooth and hairless.
Poison hemlock can be differentiated from a carrot or parsnip plant by the profuse number of purple spots on the stem. In addition, the stem is smooth and hairless. Leaves are also smooth and hairless; they are large, glossy green, finely divided and fern-like. Eight known alkaloids contribute to poison hemlock’s toxicity. Poison hemlock typically produces a bad smell that closely resembles mouse urine. This unpleasant odor is especially noticeable when the leaves are crushed.
All parts of poison-hemlock (leaves, stem, fruit, and root) are poisonous. Leaves are especially poisonous in the spring, up to the time the plant flowers.
If the plant is disguised in hay or pasture grasses and ingested, it only takes a small amount to kill. Also avoid silage with hemlock in it.
The good news for livestock producers is animals will avoid this plant as long as there is quality feed available. However, if the plant is disguised in hay or pasture grasses and ingested, it only takes a small amount to kill. Sheep may be poisoned by eating as little as 4–8 ounces of green leaves. Cattle that eat as little as 10–16 ounces may be affected. All classes of livestock and wildlife are susceptible to poison hemlock.
Signs of poisoning usually appear within an hour after an animal eats the plant. Animals die from respiratory paralysis in 2 to 3 hours. Signs to look for in animals include:
- a loss of appetite
- excessive salivation
- a rapid but feeble pulse
- evidence of muscular incoordination, and
- the appearance of great abdominal pain.
Other signs include muscle tremors, frequent urination, defecation, and "nervousness." In animals that die, breathing ceases due to respiratory paralysis before cardiac arrest.
Birth defects due to ingesting sub-lethal amounts of poison hemlock occur in all livestock and may include crooked legs (crooked calf disease, arthrogryposis), cleft palate, and kinked tails. Arthrogrypotic skeletal malformations occur in calves when poison hemlock is ingested by pregnant cows between days 40 and 70 of gestation. For sheep, goats, and pigs, these problems occur when animals are exposed to hemlock during the 30- to 60-day period of gestation. In addition, poison hemlock poisoning is indistinguishable from lupine-induced “crooked calf disease” without a necropsy.
Plowing or repeated cultivation will prevent poison hemlock from establishing. Digging poison hemlock can be effective when caught early and the plant population is small. Take care when digging or mowing poison hemlock. Wear rubber gloves and a mask when handling this plant. On a hot day, the plants’ toxins may be absorbed into the skin.
Do not burn the plant, as the smoke can contain deadly toxins. In fact, hemlock is so poisonous that some of poison hemlock’s alkaloid compounds have the ability to pass into milk when animals feed on sublethal amounts of this plant, which can adversely alter the flavor and safety of milk used for human consumption.
Treating poison hemlock with herbicides is most effective in late spring or early summer. Several combinations of herbicides are effective, including 2,4-D plus dicamba (2.5lb + 1 lb a.i./acre). Glyphosate and triclopyr have also been used with success. Herbicides should be used on seedlings or small rosettes and not on fully mature plants for ultimate success. To achieve complete eradication, repeated applications may be required until the seed bank has been depleted.
Please use caution; herbicides sprayed within 50 feet of a body of water can pose significant environmental hazards and typically require an aquatic herbicide. Be sure to contact your local weed control authority or OSU Extension for specific herbicide recommendations, and check the herbicide label for restrictions.
Western waterhemlock, Cicuta douglasii
Western waterhemlock is a member of the plant family Apiaceae. It is described as the most violently toxic of all North American plants. It only takes a piece of the root the size of a walnut to kill a 1,200-pound cow or horse. Also known as cowbane, wild parsnip, and beaver poison, this plant is herbaceous and thrives along streams, marshes, rivers, and irrigation ditches all over the Western United States and Canada.
Western waterhemlock grows from 2 to 8 feet tall, depending on its location. The stems are hollow, and it is easily identifiable by its root — a bulbous structure that is mostly hollow, with the exception of a few partitions that form distinct chambers. Thick, fleshy tubers and slender individual roots grow from the bottom of the main rootstalk.
Seeds from plants growing along irrigation canals can be transported by water or mud to other locations and can remain viable in soil for up to three years.
The leaves of western waterhemlock are arranged like a feather, dividing 1–3 times into narrow-toothed and lance-shaped leaflets 1–4 inches long. The leaflet veins run from the midrib to the notches along the leaf edges, and then branch to the teeth-like tips. Like poison hemlock, Western waterhemlock’s flowers are white and grouped in umbrella-shaped clusters.
Likewise, each flower is two-seeded. The tea-colored seeds are somewhat kidney-shaped with corky ridges. Western waterhemlock reproduces from seed and vegetatively through overwintering root structures. Seeds from plants growing along irrigation canals can be transported by water or mud to other locations and can remain viable in soil for up to three years.
The toxic substance in waterhemlock is cicutoxin, a highly poisonous unsaturated alcohol that has a strong, carrot-like odor. It is found principally in the tubers or roots but is also present in the leaves, stems, and immature seeds. If the tuber is cut or broken, it exudes a highly poisonous brown or straw-colored liquid. This liquid is deadly; animals have been poisoned after waterhemlock roots were trampled in the water, releasing the toxic liquid.
Livestock that ingest just the upper part of the plant may survive, as this part is not as toxic as the roots. But that is not as common. Typically, cattle pull the whole plant out of the soil due to the wet conditions and eat it, root and all. This is always fatal. Cattle are common victims, but horses, sheep, and swine are sometimes killed, too.
All classes of livestock and wildlife are susceptible to poisoning, with cattle, goats, and horses being the most sensitive. Most animal losses take place in the spring, as it is one of the first plants to emerge. Fortunately, animals tend to avoid this plant when other forage is available, but they will consume it when grazing is poor. Consumption and poisoning may also occur when hemlock is present in green chop, silage, or hay. Even when it is mature and dried out, it still possesses toxins.
Fortunately, animals tend to avoid this plant when other forage is available, but they will consume it when grazing is poor.
The best way to avoid livestock losses from western water hemlock poisoning is to eliminate it. If eradication is not complete, then areas known to be infested with Western waterhemlock, especially in the early spring, need to be strictly avoided. Use fencing or move livestock to other paddocks. Similarly, it is critical when cleaning ditches or clearing land to avoid exposing the toxic roots of waterhemlock, which then can be more easily ingested by livestock.
Hand-pulling Western waterhemlock is effective when the soil is moist. Be careful to pull the entire plant, including all roots, and dispose of it in a garbage bag. Several articles recommend burning hemlock after pulling, but the smoke may contain toxins that could cause severe illness and even death. Be sure to wear appropriate gloves, as contact dermatitis is possible. If your hands come into contact with the plant — especially the root — and then touch your eyes or mouth, you can become very ill.
For western waterhemlock, application of chemicals is most effective in late spring or early summer. Several types of herbicide can be effective, including Glyphosate, 2,4-D, and picloram and 2,4-D, and MCPA. Glyphosate is nonselective, so exercise caution to minimize injury or mortality of desirable plants that might help suppress new poison hemlock seedlings.
Keep animals away from treated plants for three weeks after spraying.
Also, after Western water hemlock is sprayed with herbicides, an increase in palatability can occur. Keep animals away from treated plants for three weeks after spraying. Chemical treatment of Western waterhemlock may require repeated applications to deplete the seed bank.
A word of caution: Herbicides sprayed within 50 feet of a body of water can pose significant environmental hazards. These situations typically require an aquatic herbicide. Be sure to contact your local weed control authority or OSU Extension office for specific herbicide recommendations. Check the herbicide label for restrictions.
Both poison hemlock and Western waterhemlock plants require caution when handling. Constant vigilance is required to eliminate these toxic weeds from your property. A good manager can contain or eliminate hemlock in order to keep your livestock safe.
Panter, K.E., M.H. Ralphs, J.A. Pfister, D.R. Gardner, B.L. Stegelmeier, S.T. Lee, K.D. Welch, B.T. Green, T.Z. Davis, and D. Cook. 2011. Plants Poisonous to Livestock in the Western States. U.S. Department of Agriculture, Agriculture Bulletin No. 415.
Pokorny, M.L., and R.L. Sheley. 2000. Poison Hemlock. MSU Cooperative Extension Fact Sheet MT200013AG.
Beecher, C. 2014. Garden Visitor Can Be Deadly If Eaten. Poison hemlock is easily mistaken for edible plants. Food Safety News.
DiTomaso, J.M., J.A. Roncoroni, S.V. Swain, S.D. Wright. 2013. Poison Hemlock. Integrated Pest Management for Land Managers. Pest Notes. University of California, Ag and Natural Resources, Statewide Integrated Pest Management Program. Publication 74162.
Graham, J., and W.S. Johnson. Managing Poison and Western Water Hemlocks. UNR Cooperative Extension Fact Sheet-04-09.
Whaley, D K., G.L. Piper. 2013. Western Waterhemlock in the Pacific Northwest. Pacific Northwest Extension Publication. PNW 109.
United States Department of Agriculture. Ag Research Service. 2006. Poisonous Plant Research. Water Hemlock.
Cattle that eat 300 to 500 gm may be poisoned. Signs usually appear within an hour after an animal eats the plant. Animals die from respiratory paralysis in 2 to 3 hours. Convulsions, which are common in western water hemlock poisoning, seldom occur with poison-hemlock.
Poison hemlock is a much larger plant than wild carrot. Water hemlock has a spotted stem like poison hemlock, but is a perennial that produces a cluster of fleshy tubers at crown, and the leaflets are not finely divided like poison hemlock.
"Depending on the situation, it can be a dangerous plant," Gibson said. "Most of the harm is if you ingest any part of the plant, but the worst parts or the most dangerous are the seeds or the taproot or the roots." Gibson said if you brush up against poison hemlock, you should be fine.
Toxicity. Poison-hemlock is acutely toxic to people and animals, with symptoms appearing 20 minutes to three hours after ingestion. All parts of the plant are poisonous and even the dead canes remain toxic for up to three years. The amount of toxin varies and tends to be higher in sunny areas.
Poison hemlock is toxic to a wide variety of animals including birds, wildlife, cattle, sheep, goats, pigs, horses and to humans. People are usually poisoned when they eat hemlock mistaken for plants such as parsley, wild carrot or wild anise.
It's also very toxic for humans. Simply touching the plant can make you sick.” Poison hemlock features white, umbrella shaped flower clusters with fern-like leaves.
The plant is poisonous at all stages of development and is most toxic in the spring. Poisonings typically result from ingestions; however, cicutoxin also may be absorbed through the skin. Mild toxicity from water hemlock produces nausea, abdominal pain, and epigastric distress within 15-90 minutes.
The toxins can also be absorbed through the skin and lungs, so be sure to wear gloves and a mask when handling these plants.
Water hemlock has small, white flowers that grow in umbrella like clusters. Side veins of the leaves lead to notches, not to tips at the outer margin. The thick rootstalk of water hemlock contains a number of small chambers.
The alkaloids slowly poison the nerve-muscle junctions and cause the failure of the breathing muscles. Even touching this plant may cause a skin reaction known as dermatitis (itchy skin rash) in sensitive people. Lack of antidote makes hemlock poisoning more difficult to treat.
Do not burn the plant, as the smoke can contain deadly toxins. In fact, hemlock is so poisonous that some of poison hemlock's alkaloid compounds have the ability to pass into milk when animals feed on sublethal amounts of this plant, which can adversely alter the flavor and safety of milk used for human consumption.
Mowing is not recommended due to the risk of breathing in plant particles. Cut plants will regrow. There are various herbicides that may help with preventing and managing poison hemlock. Spraying the foliage in spring and once more in late sum- mer has proven to be effective in management of this weed.
The general symptoms of hemlock poisoning are effects on nervous system (stimulation followed by paralysis of motor nerve endings and CNS stimulation and later depression), vomiting, trembling, problems in movement, slow and weak later rapid pulse, rapid respiration, salivation, urination, nausea, convulsions, coma and ...
All parts of this plant contain toxic alkaloids that can be fatal even in small amounts. The alkaloids can affect nerve impulse transmission to your muscles, eventually killing you through respiratory failure. Even touching this plant may cause a skin reaction in some people. To date, there is no antidote.
The plant can be found in every state in the country, with the exception of Alaska, Florida, Hawaii and Mississippi, according to the USDA.
Did you know that white-tailed deer can survive eating most toxic plants in our area? Deer are often seen foraging on huge amounts of nightshade, poison ivy, pokeweed, and hemlock with no apparent ill effects. They've even been known to become addicted to the psychoactive effects of some poisonous plants!
Poison Hemlock and its invasive nature
Additionally, birds are unaffected by the poison, and eat the seeds. And birds are the main reason this plant is so invasive. Once the plant has turned brown/died, the seeds will stay on top of the dried flowers throughout the winter.
Clinical signs include drooling, dilated pupils, weakness, agitation, nervousness, twitching, seizures, cardiac abnormalities, difficult breathing, and death from respiratory paralysis.
Ingesting hemlock is the most dangerous type of exposure, but every part is poisonous, especially the seeds. Touching it can lead to severe skin irritation, and inhaling air near mowed hemlock can cause respiratory irritation. Even dead plant canes can be poisonous for up to three years.
Major toxicity and death occur when a depression phase develops. The heart and the diaphragm muscles can slow down more and more, causing death. In humans, coniine affects the nervous system and causes tremors, paralysis, and breathing difficulties. Muscle damage and kidney failure may occur in severe cases.
Small stands of poison hemlock can be controlled through hand removal. Plants should be dug, taking care to remove the entire long taproot. Plant parts should be disposed of responsibly, as plant parts remain poisonous even after dried.
Chemical screening test for alkaloids in plant material provides confirmation of toxicity due to poison or water hemlock.
The term sardonic grin comes from the grisley practice in Phoenician Sardinia of disposing of criminals and old people using Hemlock Water Dropwort. The poison acts by constricting the muscles causing death by asphixia which also causes a rictus like death grin, the sardonic grin.
The oleander, also known as laurel of flower or trinitaria, is a shrub plant (of Mediterranean origin and therefore, resistant to droughts) with intensely green leaves and whose leaves, flowers, stems, branches and seeds are all highly poisonous, hence it is also known as "the most poisonous plant in the world".
All parts of the plant are toxic, especially the seeds and roots, and especially when ingested.
Is Poison Hemlock Toxic to Dogs? Poison hemlock is toxic, when ingested, to people, livestock and, yes, cats and dogs.
► Chemical There are two herbicides that can be used to control Poison hemlock they are both non-selective chemicals and kill nearly all types of plants. Glyphosate is a non-selective active ingredient found in a number of products (like RoundUp Pro® , with 41% glyphosate) that are effective in controlling hemlock.
The entire plant is poisonous. The tubers, stems, and leaves contain oenanthotoxin, a highly unsaturated higher alcohol, which is known to be poisonous and a powerful convulsant.
Closely related to poison hemlock (the plant that famously killed Socrates), water hemlock has been deemed "the most violently toxic plant in North America." A large wildflower in the carrot family, water hemlock resembles Queen Anne's lace and is sometimes confused with edible parsnips or celery.
Though Healthline states that there is no known antidote to hemlock poisoning, if you think you may have touched any part of the plant, breathed in its particles, or been otherwise exposed, you should seek medical attention immediately.
Despite serious safety concerns, hemlock leaves, root, and seeds are used to make medicine. It is used for breathing problems including bronchitis, whooping cough, and asthma; and for painful conditions including teething in children, swollen and painful joints, and cramps. Hemlock is also used for anxiety and mania.
But be extra careful: its distinctive reddish-purple spotting roots can be easily mistaken for wild parsnips, and its fern-like leaves look a lot like parsley. Poison hemlock can also be distinguished from its tasty lookalikes by smell. Once crushed, it has been described as having a musty or “mouse urine”-type odor.
This plant, along with Spotted Water Hemlock (Cicuta maculata), are poisonous to livestock and humans. Osha or Porter's Lovage (Ligusticum porter) is an edible plant, and looks very similar to poison hemlock.
Plants emerge as a cluster of leaves that form a rosette. Poison hemlock is most noticeable at this stage of growth in late fall through early spring with its parsley-like leaves which are highly dissected or fern-like. The individual leaves are shiny green and triangular in appearance.
Symptoms can range from vomiting to seizures to respiratory failure. There's no antidote for hemlock poisoning. Your healthcare provider will treat your symptoms, but the condition can be fatal. You can prevent hemlock poisoning by getting rid of any hemlock plants in your yard.
The signs of poisoning are those of severe gastrointestinal irritation and include: Red and/or ulcerated oral tissues; Salivation; Blood-tinged milk; Diarrhea; Abdominal pain; Depression or excitation; Convulsions; Death.
Poison hemlock was imported into the U.S. as an ornamental in the late 1800s from Europe, West Asia, and North Africa. Rogue plants remained relatively rare until around 30 years ago. Since that time, poison hemlock has moved from an uncommon oddity to a common threat.
The top five trees poisonous to large animals are the red maple, oak, box elder, chokecherry and black walnut. Careful attention must be paid to animals pastured close to these trees, and every effort must be made to prevent access.
Cattle have been known to eat lethal amounts of water hemlock in pastures having adequate forage; therefore, animals should be prevented from grazing over water hemlock-infested areas.
Clinical signs include drooling, dilated pupils, weakness, agitation, nervousness, twitching, seizures, cardiac abnormalities, difficult breathing, and death from respiratory paralysis.
- feeling and being sick.
- stomach pain.
- drowsiness, dizziness or weakness.
- high temperature.
- chills (shivering)
- loss of appetite.
- Behavioral changes – These include crankiness and restlessness.
- Loss of appetite.
- Minor skin irritation.
Nitrate. Nitrate poisoning of animals is actually nitrite poisoning occurring when nitrate is reduced to nitrite in the gastrointestinal tract. The nitrite is absorbed into the bloodstream where it reacts with hemoglobin to form methemoglobin.
If plant juices contact skin and the skin is then exposed to sunlight (specifically ultraviolet light), severe blistering can occur, as well as skin discoloration that may last several months.
Mechanical: Caution: toxins can be inhaled when mowing poison hemlock. Mowing is not recommended due to risk of breathing in toxins. In addition, cut plants can regrow.
Producers should evaluate their pastures to determine if adequate forage exists before turning livestock out to graze. If there is a lack of adequate forage, livestock may be more likely to eat poisonous plants, Knight said.
- Ragwort. While ragwort has a bitter taste and is rarely eaten by horses when it is growing, when it is wilted or dried it becomes more palatable. ...
- Foxglove. ...
- Deadly nightshade. ...
- Buttercups. ...
- Acorns. ...
- Yew. ...
- Privet. ...
With proper management to insure adequate sunlight for forage, a pasture with trees can produce substantial beef gains and tree crop returns. On pastures or grasslands without existing trees, plant rows of pines or nut-producing trees, spaced to allow adequate sunlight penetration for forage growth.