Thursday, July 2, 2015

Identifying Poison-Hemlock by Audrey Stokes

Poison-Hemlock (Conium maculatum).
Scientists recommend that you learn to identify and avoid plants that produce dangerous toxins. Your life may depend on it! Each year dozens of people die or are sickened by weeds they didn’t know would cause them harm. Gardeners and outdoor enthusiasts need to be well-informed in order to stay safe. Recently in Larimer County, a dog died from ingesting water hemlock.

Why are some weeds poisonous?  Most plants produce their own naturally occurring pesticide to deter predators so they won’t be eaten. No plant could survive without producing some defense mechanism. Most lists of Colorado’s toxic weed species that I researched were topped by the very dangerous Poison-hemlock (Conium maculatum). I found this especially alarming due to the fact that I have this weed growing on my property!  Originally imported from Europe as an ornamental plant, it has spread rampantly across North America.
Hemlock and other poisonous weeds are often cousins of edible foods and share similar flowers, leaves, fruit and seeds. Hemlock is a biennial weed with fern-like leaves that can be easily mistaken for parsley.  Poison-hemlock can be confused with wild carrot (Daucus carota, or Queen Anne's Lace), as with many other members of the parsley family that resemble it.   In contrast, wild carrot has one dense flower cluster on a narrow, hairy stem, usually with one purple flower in the center of the flower cluster, and is usually 3 feet tall or less.
Hairless Hollow stalk on Poison-hemlock
It has hairless hollow stalks with purple/red blotches – a good identification tool. It can get quite tall, sometimes up to 8 feet or higher. It produces many umbrella-shaped flower clusters in an open and branching arrangement.

Why is Poison-hemlock so dangerous?
  • The plant produces a number of toxic substances, but the most deadly is the alkaloid coniine – a neurotoxin that disrupts the central nervous system. 
  • All parts of the plant are poisonous and even the dead canes remain toxic for up to three years.  
  • It is acutely toxic to people and animals, with symptoms appearing 20 minutes to three hours after ingestion.  
  • Eating even the smallest amount can result in rapid respiratory collapse and death. It is also toxic to the skin and respiratory system. 
  • The typical symptoms for humans include dilation of the pupils, dizziness, and trembling followed by slowing of the heartbeat, muscle paralysis, and death due to respiratory failure. If you suspect poisoning from this plant, call for help immediately because the toxins are fast-acting!
  • Several herbicides are effective in controlling Poison- hemlock. 
  • When digging or mowing large amounts of this plant it is best to wear gloves and a mask or take frequent breaks to avoid becoming ill. 

If you are still not alarmed about this dangerous plant, keep in mind:
  • This is the species responsible for the death of the Greek philosopher Socrates! 
  • Native Americans were known to dip their arrows in hemlock!

Keep yourself educated about all the poisonous plants in our region to help ensure the safety of your families and pets!

See these articles to learn more about identification and control of  Poison-hemlock:

King County, Washington – Noxious Weeds:

Weed Society of America: The Deadly Problem of Noxious Weeds: