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Poison hemlock (Conium maculatum)
Biennial herb 3-10’ tall stems are hollow, hairless, ridged, reddish-purple mottling on lower stem and branched extensively.
Poison hemlock is Prohibited (Red counties) and Restricted (Orange counties)
Other names for this plant include:
- Common names: deadly hemlock, fool's parsley, spotted hemlock, spotted parsley
- Invades a range of habitats from roadsides, fields, stream banks, disturbed areas, to riparian woodlands, and floodplains.
- An individual plant can produce over 30,000 seeds.
- All parts of the plant are toxic to animals and humans.
Classification in Wisconsin: Prohibited/Restricted (Restricted in Buffalo, Crawford, Dane, Grant, Green, Iowa, Jefferson, Kenosha, La Crosse, Lafayette, Milwaukee, Monroe, Ozaukee, Racine, Richland, Rock, Sauk, Sheboygan, Trempealeau, Vernon, Walworth, and Waukesha counties; Prohibited elsewhere)
Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for poison hemlock was based upon this literature review developed by the department.
Leaves: Pinnately compound, toothed, 8-16” long and broadly triangular. Leaf veins end at the tips of the tooth margins. Leaves are shiny, green, and emit an unpleasant odor when crushed.
Flowers: Numerous, small, 5-petaled white flowers in umbels 4-6” across, are at the end of an individual stem that extends from a common stalk. Bloom May-August.
Fruits & seeds: Seeds are ridged and flat. A single plant produces over 30,000 seeds.
Roots: Thick, white taproot.
Similar species: Water hemlock (Cicuta maculate; native) has leaf veins that end in the notches between the tooth margins of the leaflets. Giant hogweed (Heracleum mantegazzianum; invasive) has a hairy stem and larger, less divided leaves.
Counties in WI where poison hemlock has been reported (as of July 2011). Both vouchered and unvouchered reports included.
Do you have poison hemlock in your county but it isn't shaded on the map? Send us a report.
Mechanical: Hand pulling, or mowing close to the ground multiple times for several seasons. Wear gloves when handling this plant.
Chemical: Foliar spray of 2, 4-D plus dicamba before buds are produced.
For more information on control techniques, visit the Poison hemlock factsheet by University of Wisconsin-Extension.
View poison hemlock pictures in our photo gallery!
Sources for content:
- USDA Forest Service, Northeastern Area Forest Health Staff. Weed of the Week: Poison hemlock
- Center for Invasive Species and Ecosystem Health, Invasive.org. Poison hemlock
Links for More Information