A Threat to Animals and Humans

Poison Hemlock

​The poison hemlock flower may be attractive to insects, but animals including humans should beware. The plant is highly toxic. Photo by A. Windham, courtesy UTIA.


In 399 B.C.E, Athenian philosopher Socrates was famously condemned to die by drinking a cup of liquid distilled from the poison hemlock plant. Many people know the story of Socrates' death. But what you may not realize is that plant that caused his death is commonly found growing as a weed in pastures throughout the state of Tennessee and it is just as deadly today as it was 2,400 years ago. 
"Poison hemlock is one of the most toxic plants in North America and all parts of the plant are toxic," says Neil Rhodes, Jr., University of Tennessee professor and Extension weed management specialist. Both animals and humans have died due to accidental ingestion. Deaths are often associated with mistaken identity, says Rhodes. "Children have been fatally poisoned by making whistles or pea shooters from the hollow stems. Other human deaths have occurred where the plant is mistaken for wild parsnips or parsley."
The plant is also a danger to grazing livestock. Less than a pound of consumed hemlock can be enough to poison cattle, cautions Rhodes. Thankfully, however, human and livestock deaths from hemlock poisoning is rare, due to the plant's unpalatability. 
The best way to prevent exposure to the plant is by being able to recognize and destroy it. The weed is capable of reaching heights of three to four feet and it produces long, triangular compound leaves that range from eight to 16 inches long. Poison hemlock's most distinctive feature is the many handsome, small, white flowers it blooms. "Knowing how to recognize poison hemlock by sight allows for physical removal and disposal of initial introductions of this weed," says Rhodes. "Fortunately, most pasture infestations of this weed are very localized rather than being scattered across the entire pasture."
Sometimes, however, infestations are too large to remove by hand. In those cases herbicides may be needed. Before spraying, be sure to thoroughly read the herbicide label and follow all directions and precautions. Rhodes also suggests the Extension resource herbicidestewardship.utk.edu for more information. 
For more information about poison hemlock or other weeds, go online to extension.utk.edu/publications and search “weeds,” or contact your local county UT Extension office. The publication Pasture Weed Fact Sheet: Poison Hemlock (W 325) can be viewed directly at https://extension.tennessee.edu/publications/Documents/W325.pdf.
UT Extension provides a gateway to the University of Tennessee as the outreach unit of the Institute of Agriculture. In cooperation with Tennessee State University, UT Extension works with farmers, families, youth and communities to improve lives by addressing problems and issue at the local, state and national levels.

The UT Institute of Agriculture provides instruction, research and outreach through the UT College of Agricultural Sciences and Natural Resources, the UT College of Veterinary Medicine, UT AgResearch, including its system of 10 research and education centers, and UT Extension offices in every county in the state.


Dr. G. Neil Rhodes, Professor of Plant Sciences, Extension Weed Management Specialist, 865-974-7324, nrhodes@utk.edu