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Purdue Landscape Report: Poison hemlock was introduced to North America as a garden/ornamental plant. It is a native of Europe, and it is a member of the Apiaceae (parsley) family.

Purdue experts Bill Johnson and Marcelo Zimmer wrote about poison hemlock in a Purdue Pest & Crop newsletter.

They wrote that poison hemlock can be noticed very early in the spring every year, as it is typically one of the first weeds to green up, usually in late February to early March if temperatures are favorable. They said the largest threat of this weed is the toxicity of its alkaloids if ingested by livestock or humans, but it can also reduce the aesthetic value of landscapes and has been reported to creep into no-till corn and soybean fields as well.

poison hemlock

Poison Hemlock

Purdue Extension’s fact sheet on poison hemlock states that it can also be found along roads, streams, trails, ditches, forest edges, and waste areas.

The Purdue experts said that poison hemlock is a biennial weed that exists as a low-growing herb in the first year, and bolts to three to eight feet tall in the second year, when it produces flowers and seed. It is often not noticed until the bolting and reproductive stages of the second year. Poison hemlock is often confused with wild carrot, but can be distinguished by its lack of hairs and purple blotches that occur on the stems.

The experts pointed out that poison hemlock contains five alkaloids that are toxic to humans and livestock, and it can be lethal if ingested. They warn that the plant’s alkaloids may also be absorbed through the skin, so if you find yourself hand-pulling poison hemlock, it would be a good idea to wear gloves. All parts of the plants contain the toxic alkaloids with levels being variable throughout the year. Symptoms of toxicity include nervousness, trembling, and loss of coordination followed by depression, coma, and/or death. Initial symptoms will occur within a few hours of ingestion.

For history buffs, the Greek philosopher Socrates was sentenced to death by hemlock poisoning.

Cases of poisoning due to poison hemlock ingestion are rare as the plants emit a mousy odor that makes it undesirable and unpalatable to livestock and humans. Consumption and toxicity in animals usually occur in poorly managed or overgrazed pastures where animals are forced to graze poison hemlock because desirable forage is lacking.

To view this full article and other Purdue Landscape Report articles, please visit Purdue Landscape Report.

Subscribe and receive the newsletter: Purdue Landscape Report Newsletter.

The Purdue Landscape Report
Purdue Pest & Crop Newsletter
Invasive Plant Species Fact Sheets: Poison Hemlock, The Education Store, Purdue Extension Resource Center
Poison Hemlock (Conium maculatum), United States Department of Agriculture (USDA)
Invasive plants: impact on environment and people, The Education Store, Purdue Extension’s resource center
Woodland Management Moment: Invasive Species Control Process, Video, Purdue Extension – Forestry and Natural Resources (FNR) YouTube Channel
Invasive Species, Playlist, Purdue Extension – FNR YouTube Channel
What are invasive species and why should I care?, Got Nature? Blog, Purdue Extension – FNR
Report Invasive, Purdue College of Agriculture – Entomology

John Woodmansee, Extension Educator, Whitely County
Purdue Extension

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