Stevens County Noxious Weed Control Board
This web site will help you identify & control noxious weed with information and photographs to aid you.

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Poison hemlock
Conium maculatum                      
Parsley family

Key identifying traits

  • A big plant normally 6 to 8 feet tall
  • Flowers are small and white consisting of 5 petals and borne in numerous umbrella like clusters
  • Stems are erect, stout, and purple spotted with distinct ridges and extensively branched
  • Leaves are fern like and have a musty odor
  • Has a large white fleshy tap root
  • Seeds are paired, 1/8 inch long, brown, ribbed and concave

Biology and ecology

  • A biennial, occasionally growing up to 10 feet tall
  • Tolerates poorly drained soils and often found along streams and ditch banks
  • Also found on roadsides and gradually invading perennial crops and pastures
  • All plant parts including the white fleshy root are poisonous to humans and livestock
  • It was the liquid extracted from this plant that Socrates reportedly used to kill himself in 399BC

Control

Prevention Learn to identify plants; know your property; beware of parsley type plants invading along waterways or wet roadsides

Biological The poison hemlock moth has been a very effective defoliator of Poison hemlock plants where introduced on large infestations in Washington state.

Cultural Good vegetative cover lessens likelihood of initial infestations

Mechanical Tillage, digging and pulling are all effective controls but care must be used in handling

Chemical Several effective at label rates but must use care near water; refer to the PNW Weed Management Handbook for specific chemical recommendations

ph1.jpg (164482 bytes)

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purple spotted stem

ph3.jpg (59431 bytes)
fern-like leaf

ph4.jpg (44993 bytes)
flowers


Where found
Occasionally found in Stevens County, generally in wet, poorly drained areas including ditch banks, bogs and wet pastures.

MSdoc     pdf

 

weedboard@co.stevens.wa.us
Last Edit: March 25, 2015
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