Toxic and invasive, poison hemlock is one to control early

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Poison hemlock leaf

Poison hemlock is not a plant to tolerate. Its likely to spread and become a bigger problem.

Poison hemlock is invasive, highly toxic and, lately, on the increase in many states. You don’t want it.

All parts of the plant are toxic to both humans and livestock. Human deaths have occurred when people mistook poison hemlock for edible wild parsnip or wild dill. Children have been fatally poisoned when they made pea shooters from its hollow stems. For cattle, poison hemlock is toxic if grazed or consumed in hay.

And, yes, this is the same plant used to execute Greek philosopher Socrates in 399 B.C.

It’s just as toxic now as it was then.

An import from Europe, poison hemlock (Conium maculatum) is a biennial in the carrot family. The family includes wild carrot (Queen Anne’s lace). 


Poison hemlock and wild carrot have similar, fernlike leaves and umbrellalike clusters of small, white flowers. Poison hemlock has smooth stems with purple spots while Queen Anne’s lace has hair along its stem and leaf bases without the purple spots. 

One of the first plants to green up in the spring, poison hemlock forms a rosette in its first year and then bolts and flowers in its second. It commonly reaches heights 4 to 6 feet and may grow taller. 

Each poison hemlock plant can produce up to 38,000 seeds, viable up to three years. Mowing has been one of the chief ways to spread those seeds.

Poison hemlock commonly appears on roadsides, in fencerows, along creeks and, increasingly, in pastures and hayfields. It often begins as a small infestation and quickly expands. For that reason, it’s a problem to tackle soon after you notice it.

Cattle that ingest poison hemlock will start to show symptoms within two hours. Horses may show symptoms within 30 to 40 minutes. Symptoms include dilation of the pupils, reduced heart rate, trembling, nervousness, coma and, eventually, death from respiratory paralysis.

Livestock typically won’t graze poison hemlock because of its unpalatability. But they will eat it if no other forage is available, if it’s the only thing green or when they consume it through hay.


Poison hemlock is most susceptible to spraying when it’s in the rosette stage, but DuraCor® herbicide has been effective even later. For the best results, apply DuraCor at the labeled rate of 12 fluid ounces to hemlock rosettes in the fall or early spring. Use higher rates in labeled rate range — 16 to 20 ounces — after the plant has bolted or if you want longer residual control.

Be aware that toxic plants may become more palatable after spraying. Consider exclusion of animals from these affected areas until poison hemlock has melted down.”


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® Trademarks of Corteva Agriscience and its affiliated companies. Under normal field conditions, DuraCor® is nonvolatile. DuraCor has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. Label precautions apply to forage treated with DuraCor and to manure and urine from animals that have consumed treated forage. DuraCor is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.

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