Poison Hemlock

Information

Conium maculatum - Apiaceae Family - Biennial

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Identification

Flowers: Small, white flowers found in umbrella-like clusters.
Seeds: Long, barrel-shaped, ribbed, 1/8 inches long.
Leaves/Stems: Triangular, lacey fern-like leaves. Stems are ribbed, green with purple spots, and hollow.
Flowering Time: Biennial and doesn’t flower until the second year. After the first year, flowers appear June – August.
Life cycle/Other: Flower stems persist through the winter, allowing for a long seed dispersal period (from September through February). This plant is often mistaken for wild parsnip or wild carrot.

Impacts

Toxic to humans, wildlife, and livestock, affecting the central nervous and reproductive systems. Sensitive people may experience contact dermatitis when handling this plant.
Invades rangelands, pastures, roadsides, and cultivated fields, reducing forage for livestock and wildlife.
Poison hemlock reproduces solely via seed. One plant may produce up to 30,000 seeds, which remain viable for 3-6 years.

Most effective control methods

Hand pulling is the most effective method of controlling small infestations. Protective clothing should be worn when working in areas with this weed, and inhalation of plant particles should be minimized.
Minimize soil disturbance, which encourages further germination of seeds at infested sites. Plowing or repeated mowing of newly germinated plants will prevent Poison hemlock from reestablishing.
For larger infestations, broadleaf selective herbicides such as 2,4-D and triclopyr are most effective when used on seedlings or small rosettes. Herbicides are not effective on fully mature plants.

Control methods and timing

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Chem

Prevention (Prev) Monitor and destroy new plants before seed production.

Mechanical (Mech) Hand pulling, digging, cutting, mowing and tilling.

Cultural (Cult) Biological control agents, livestock grazing, and revegetation practices.

Chemical (Chem) Selective herbicides based on the plant and the specific location. Check our weed fact sheets for specific control information.

Poison hemlock: flower

Poison hemlock: foliage

Poison hemlock

Poison hemlock: stem

Poison hemlock: fruits

Poison hemlock: infestation

Poison hemlock