Poison Hemlock

(Conium Maculatum)

Poison Hemlock is a Class “B” Noxious Weed in Benton County

All parts of this plant are poisonous to humans & animals when consumed. This plant can be toxic to the skin and respiratory system.

Identification: Poison Hemlock is an erect biennial that reproduces by seed. It is a member of the parsnip/carrot family. A rosette of leaves is formed in the first year, with stems and flowers following in the second year. Stems grow to be tall, hollow, and green with purple blotches on them. Leaves are pinnately-divided, fern-like, and have a musty odor. Flowers form at the ends of stalks and are small, with five petals, white, and appear in umbrella-like clusters. Seeds are oval, brown, ribbed and flattened. It has a thick taproot.

Control Methods:

·      Mechanical:

Repeated tilling, mowing, digging, cutting, or hand removal, are effective if done throughout the season and before seed production. Repeated cultivation are more effective when followed by mulching and replanting an area with desired vegetation.

·      Chemical:

There are pre-emergent herbicides available. You can also apply herbicides in the spring when the plant is in the rosette stage or before buds are produced. When the stems are elongating, the control of these plants with any herbicide is likely to diminish. Don’t cut the stems after an application, since this will prevent root absorption. Refer to the Pacific Northwest Weed Management Handbook for further information. Always follow the herbicide labels.


Dispose of Poison Hemlock so that children & animals are not at risk. This plant remains toxic years after being pulled. Always wear gloves & protective clothing when handling. A mask may be necessary when digging or mowing large infestations. Don’t compost any part of the plant.

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