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Report an Invasive Species

Poison hemlock

Poison hemlock

Poison hemlock

(Conium masculatum )

Priority: -  Prevent

Tags: Terrestrial | Toxic

Identification and Reproduction

Identification: 

  • Poison hemlock is a toxic biennial in the Apiaceae family (carrot).
  • Puts off an unpleasant odor when crushed. 
  • This plant typically grows between 1 to 3 m tall. 
  • Hallow stems are green with purple reddish blotches and are hairless.  

  • Leaves are light green, triangular and fern-like. 

 

  • Flowers are small and clustered in an umbrella-shaped head.

Reproduction: 

  • Poison hemlock reproduces by seed. 
  • A single plant can produce 40,000 seeds that will remian viable for up to 6 years. 
  • Seeds are easily transported by machinery, animals, water movement and humans. 

Habitat & Ecology

  • Thrives in moist soils in sunny locations. 
  • Commonly found along ditches, road sides, fields and disturbed ares. 

Impacts

Social: 

Poison-hemlock is toxic and all parts of the plant are poisonous. Poses as a risk to both people and animals. If you suspect someone has eaten poison hemlock, call the BC Poison Control Centre immediately (1-800-567-8911). 

  • Dead canes can remain toxic for up to 3 years. 
  • Can cause sever skin irritation and issues to the respiratory system. 
  • Out completes native forage species and will be hazardous to livestock. 
  • Often confused with edible plants in the carrot family. 

Management

When performing any control treatment to poison hemlock, minimize skin exposure; wear gloves, safety glasses and long sleeves. Wash hands, tools and clothes thoroughly after handling poison hemlock. 

Mechanical/Manual Control: 

  • For small infestations hand pulling or digging up the plants is effective. Be sure to remove the entire root system. 
  • If plant roots are too large to remove cut at least 3cm below ground. 
  • Manual removal is best done prior to flowering to reduce seeds being left on site. 
  • Use and apply a layer of mulch to suppress new growth after removing plants. 
  • Mowing is not recommended as this can lead to respiratory problems by breathing in the toxins. 
  • Do not compost this plant. Place removed plant fragments in a bag for disposal. 

Resources

Download the Capital Region Invasive Species Program's Alert Sheet on Poison Hemlock here

Sometimes confused with giant hogweed. Please check out Maine's Department of Agriculture, Conservaion and Forestry's resource guide comparing lookalike species here

Download the King County Noxious Weed Alert's Factsheet on Poison Hemlock here. Please note this a US resource and Canadian guidelines and regulations may differ. Be sure to carefully read all labels before use. 

Header photo (Françoise Caclin).