Poison Weed Alert!

Poison hemlock is not new to Lewis County, however Weed Control staff have spotted several new infestations popping up this season. If you aren’t already familiar with this weed, please take the time to learn a few “tricks of the trade” so you don’t find yourself fighting a patch of poison hemlock without the appropriate weapons (and safety gear).

Poison hemlock (Conium maculatum), a Class B noxious weed, is a widespread toxic biennial plant in the Carrot Family often found along streambanks or drainage ditches, open fields, vacant lots, and along roadsides. Eating even a small amount of any part of this plant can kill people, livestock, and wildlife. Poison hemlock stems are not hairy (like the wild carrot), have reddish or purple spots and streaks, and are hollow. Leaves are bright green, fern-like, finely divided, toothed on edges and have a strong musty odor when crushed. Flowers are tiny, white and arranged in small, umbrella-shaped clusters on ends of branched stems.

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As a biennial weed, poison hemlock grows as a basal rosette during its first year and as an erect, towering flowering plant that can measure 6-10' tall in its second year. Native to Europe and western Asia, it is now found in almost every state in the US.

In late spring, second year plants produce numerous umbrella-shaped clusters of tiny, white, 5-petaled flowers. Flowering poison hemlock may be confused with wild carrot (Daucus carota, aka Queen Anne's Lace). In contrast with poison-hemlock, wild carrot has one densely packed umbrella-shaped 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. Wild carrot also flowers later in the summer.

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Poison-hemlock is acutely toxic to people and animals, with symptoms appearing 20 minutes to three hours after ingestion. All parts of the plant are poisonous and even the dead canes remain toxic for up to three years. The amount of toxin varies and tends to be higher in sunny areas. Eating the plant is the main danger, but it is also toxic to the skin and respiratory system. When controlling poison hemlock, minimize exposure by wearing gloves and taking frequent breaks when pulling or mowing large amounts of plants. Avoid taking any actions on hot days as toxins can be absorbed by the skin under hot humid conditions.

The typical symptoms for humans include dilation of the pupils, dizziness, and trembling followed by slowing of the heartbeat, paralysis of the central nervous system, muscle paralysis, and death due to respiratory failure. For animals, symptoms include nervous trembling, salivation, lack of coordination, pupil dilation, rapid weak pulse, respiratory paralysis, coma, and sometimes death. For both people and animals, quick treatment can reverse the harm and typically there aren’t noticeable aftereffects. If you suspect poisoning from this plant, call for help immediately because the toxins are fast-acting – for people, call 911 or poison-control at 1-800-222-1222 or for animals, call your veterinarian.

Lewis County Noxious Weed Control encourages all property owners to remove poison hemlock where possible and to avoid introducing it to new landscapes. Please contact our office to get site specific recommendations on how to remove it. If you think you’ve observed a new infestation of poison hemlock in Lewis County, please report it to us by calling Lewis County Noxious Weed Control at #(360) 740-1218, or email Lewis County Noxious Weed Control at casey.risley@lewiscountywa.gov

Posted: July 14, 2021