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Johnson County

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Johnson County
11811 S. Sunset Drive
Suite 1500
Olathe, KS 66061

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(913) 715-7000
(913) 715-7005 fax

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Kansas State University Agricultural Experiment Station and Cooperative Extension Service

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Poison Hemlock

     You’re probably familiar with poison ivy and how abundant it is. You might have heard of some other poisonous plants like poison oak or poison sumac though neither occur in Kansas. But there is another poisonous plant that can be abundant in our area: poison hemlock. While not listed as a noxious weed in Kansas, the side effects of ingesting this plant mean that if you identify some on your property it would be best to remove it.

How to Identify Poison Hemlock:

     Similar looking flowers to Queen Anne’s Lace and overall similar appearance to wild carrots, poison hemlock has lacey leaves, and clusters of white flowers. Poison hemlock has a smooth, hollow stem (unlike wild carrots, which are covered in hair), and there are purple splotches on it. The white flowers give off a very distinctive smell. For the first year, poison hemlock grows low to the ground in rosettes. In the second year, it is upright and can reach a height of 10 feet.

Risks of Poison Hemlock:

     All parts of poison hemlock are toxic and have the ability to affect the nervous system. Poison hemlock poses a serious risk to livestock if ingested, though most animals tend to avoid eating it. Risks include birth defects in pregnant animals and death from nervous system failure. It is best to remove it from pastures to keep animals safe. In humans, poison hemlock is most toxic when ingested, though inhalation or contact with skin can cause reactions as well.

Control Methods:

     Wear gloves if pulling by hand, and a respirator if mowing it down. Mow to ensure it does not go to seed. Control beginning in spring and when the plant is in rosette stage. Several herbicides are approved and suggested for control of poison hemlock including Aminopyralid plus Metsulfuron (ex Chaparral) and Picloram plus 2,4D (ex Grazon P+D). For additional herbicide information, access the K-State Research and Extension Chemical Weed Control Guide. Always follow chemical label instructions for proper application.