Poison hemlock a problem for livestock

As you travel around Henry County and most of the state, you probably notice the tall white flowered plants beside the roadways, along the fences, and out into some fields.  The plant is Poison Hemlock, and it looks as if it is rapidly becoming the new Nodding Head Thistle as a problem for farmers. 

Steve Moore

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“Poison hemlock is potentially poisonous to livestock, particularly when animals may graze poison hemlock plants when other forages are limited, or if large quantities of hay containing poison hemlock are consumed by animals,” says Dr. J. D. Green, UK Agronomist. “In addition, poison hemlock can crowd out desirable plants in areas where it becomes established.”

Introduced to the United States as an ornamental in the 1800s, poison hemlock is widespread throughout most of the state and much of North America. In the past, it was typically found along roadways, abandoned lots, fence rows and other non-cropland sites. But in recent years, its population has exploded across Kentucky, and it is now in many pastures and hayfields.

Poison hemlock can be toxic if ingested by livestock or humans. All parts of the plant are toxic, at any time of the year.  Athenian Philosopher Socrates was put to death in 399 B.C. using a hemlock based liquid.  Cattle, goats and horses are considered to be the most susceptible animals but other animals can consume it. If ingested, poisoning symptoms appear within 30 minutes to two hours, depending on several factors including the animal species and quantity consumed. Lethal doses for cattle range between 0.2 and 0.5 percent of the animal’s weight. Poisoning symptoms include nervousness, trembling, muscle weakness, loss of coordination, pupil dilation, coma and eventually death from respiratory failure. If ingested by a pregnant animal, it can cause fetal deformities.

The best time of the year to effectively control poison hemlock using herbicides is in the early spring when plants are smaller and in the rosette growth stage, particularly when applying herbicides that contain 2,4-D. In the rosette growth stage, plants can be more difficult to find since poison hemlock is growing close to the ground, but producers can easily recognize it in fields due to its parsley-like leaves.

Our animals seem to be pretty good at avoiding this poisonous plant, but if it is put in a bale of hay they may not have much choice on a bitter cold, snowy day next winter.  Best to mow around the plant to keep it out of the animals’ food supply.  But remember where the problem areas are so they can be treated in a timely fashion early next spring.