Noxious Weeds Profile - Poison Hemlock

Table of Contents


  • English - poison hemlock
  • French - ciguë maculée
  • Latin - Conium maculatum L.


Poison hemlock (A - plant before flowering; B - inflorescence of several compound umbels).

Poison hemlock (A - plant before flowering; B - inflorescence of several compound umbels).

Current Status

  • Ontario Weeds Act - noxious
  • Other provinces - noxious in Quebec
  • Canadian Federal Seeds Act - Class 1
  • U.S. Federal Noxious Weed - no
  • U.S. Noxious State Reg - 7 states (including Ohio)


  • Pub 505 - all parts of the plant are poisonous.
  • NE Weeds - Plants parts have a disagreeable odour when crushed. All aprts of the plant contain toxic alkaloids, including coniine, that cause respiratory failure in humans and other animals when ingested.
  • Canadian Poison Plant - Cattle, goats, horses, swine, and sheep as well as rabbits, poultry, deer, and humans have been poisoned after ingesting poison-hemlock. Animal species vary in their susceptibility to acute toxicity (Keeler et al. 1980).
  • Cornell Poison Plant - All plant parts are poisonous. However, the seeds contain the highest concentration of poison. The conium alkaloids are volatile and can even cause toxic reactions when inhaled.
  • Indiana Toxic Plants: TOXICITY RATINGS: Moderate to high. ANIMALS AFFECTED: All animals may be affected. Grazing animals, swine and animals that may eat the seeds (especially poultry) are more at risk than pets. DANGEROUS PARTS OF PLANT: All parts, especially young leaves and seeds. CLASS OF SIGNS: Nervousness, trembling, incoordination, depression, coma, death, birth defects.


  • Occasionally found along roadsides and woodlots. In early 80's was spread in Ontario in a seedlot of alfalfa.

Growth Habit

  • Biennial

Method of Propagation

  • Seeds


  • Not listed on any herbicide labels. Best control is by cutting or pulling and destroying the plant residue
Other Comments
  • One of the more toxic members of the carrot family.

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