Poison Hemlock: A Growing Threat in Ohio

Poison Hemlock is an invasive weed in many parts of the U.S., but is currently spreading in Ohio. Ingesting the plant or its seeds is deadly to humans and livestock.


Photo by Lev via Adobe Stock

Photo by Lev via Adobe Stock

Poison hemlock (Conium maculatum), a highly toxic invasive plant, has been spreading across Ohio, posing significant risks to both humans and livestock. Originally native to Europe, North Africa, and Western Asia, this noxious weed has found favorable conditions in the Buckeye State, flourishing in fields, along roadsides, and in waste areas.

Identification and Characteristics

Poison hemlock is a biennial plant, meaning it has a two-year life cycle. It can grow up to 10 feet tall, with smooth, hollow stems adorned with purple spots and finely divided, fern-like leaves. The plant produces small, white flowers in umbrella-shaped clusters during its second year. While it might resemble other harmless plants such as Queen Anne’s lace, its toxicity is what sets it apart and makes accurate identification crucial.

The Spread in Ohio

The spread of poison hemlock in Ohio has been rapid and alarming. Favorable conditions such as moist soil, abundant sunlight, and disturbed ground have allowed the plant to proliferate.

Factors contributing to its spread include:

  • Human Activity: Construction, agriculture, and roadside maintenance activities disturb the soil, providing an ideal environment for poison hemlock to take root and spread.
  • Natural Dispersal: The plant produces a large number of seeds that are easily dispersed by wind, water, and animals.
  • Lack of Awareness: Many people are unaware of the plant’s presence and dangers, leading to unintentional spreading through activities such as mowing and tilling.

Threats to Humans

Poison hemlock is one of the deadliest plants in North America. All parts of the plant contain toxic alkaloids, with the highest concentrations in the seeds and roots. These alkaloids can cause severe respiratory distress, nervous system disruption, and even death if ingested. Skin contact can also result in dermatitis and other allergic reactions.

Symptoms of poison hemlock poisoning in humans include:

  • Nausea and vomiting
  • Tremors and muscle paralysis
  • Dilated pupils
  • Weak pulse
  • Respiratory failure

Because of its similarity to other harmless plants, accidental ingestion is a significant risk, particularly for foragers and children.

hemlock-seeds_osu extension.png

Poison Hemlock Seeds

Ohio State University Extension

Threats to Livestock

Livestock, including cattle, sheep, horses, and goats, are at high risk from poison hemlock. Animals that graze on contaminated pastures or consume contaminated hay can suffer from severe poisoning.

Symptoms in livestock mirror those in humans and include:

  • Nervousness and trembling
  • Rapid or weak pulse
  • Salivation and bloating
  • Respiratory paralysis leading to death

The presence of poison hemlock in grazing areas can lead to substantial economic losses for farmers due to livestock deaths and the need for veterinary care.

Management and Control

The spread of poison hemlock in Ohio represents a growing environmental and public health concern. Effective management requires cooperation among landowners, government agencies, and the public to prevent its proliferation and mitigate its risks. Awareness, education, and proactive control measures are essential to protect both human health and livestock from this dangerous plant.

Controlling the spread of poison hemlock requires a multifaceted approach:

  1. Education and Awareness: Increasing public awareness about the identification and dangers of poison hemlock is crucial. Educational programs and resources for landowners, farmers, and the general public can help prevent accidental poisoning.
  2. Mechanical Control: Mowing, cutting, and removing plants before they set seed can help reduce their spread. However, care must be taken to wear protective clothing to avoid skin contact.
  3. Chemical Control: Herbicides can be effective, particularly when applied in the plant’s first year of growth. It is essential to follow local guidelines and regulations when using chemical treatments.
  4. Monitoring and Early Detection: Regular monitoring of susceptible areas, such as pastures and roadsides, can help detect and manage new infestations before they become widespread.
  5. Restoration and Prevention: Promoting the growth of native plant species and maintaining healthy ecosystems can prevent poison hemlock from establishing itself.
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Marion is a digital content manager for RFD-TV and The Cowboy Channel. She started working for Rural Media Group in May 2022, bringing a decade of experience in the digital side of broadcast media as well as some professional cooking experience to the team.