Poison Hemlock

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Joanna talks with Simpson County Agricultural & Natural Resources Agent about poison hemlock identification and control.
The toxicity of poison hemlock has been known for quite some time. This weed is credited with the death of Socrates in 329 B.C. Poison hemlock is a biennial weed meaning that its life cycle lasts for two years. It is most easily killed during the first year in the rosette stage but is most commonly noticed when it is large and flowering in the second year of growth. The stalk is hollow and tough and is mostly green with characteristic purple splotches. The leaves are small and dissected, and the plant has small white blooms. .2% - .5% of an animal’s body weight must be ingested in order to be lethal but smaller doses can cause other issues. Our biggest concern is calves and other small ruminants when other good grasses are not available. It also retains toxicity when dry, so it is a concern in hayfields as well. The weed poison hemlock is most often confused with is Queen Anne’s Lace aka wild carrot aka chigger weed. The leaves and blooms of both weeds are very similar, but Queen Anne’s Lace doesn’t get as nearly as tall as poison hemlock and features an all green stem that is much more herbaceous. Poison hemlock is best controlled with 2,4-D based products in November, but can also be effective March-April. Refer to publication AGR-207 for more information on identification and control.
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Warren County Cooperative Extension Service