It’s that time of year when poison hemlock, a dangerous noxious weed that can be fatal to humans and all classes of livestock, is once again in full growth around the state, officials with the Idaho Weed Awareness Campaign warn.

"Poison hemlock is a hazardous noxious weed that Idahoans absolutely should not take lightly. It can kill a horse or a cow within hours of them eating it," said Roger Batt, statewide coordinator for the Idaho Weed Awareness Campaign. "And there are documented cases where people have died from eating poison hemlock because they mistook the weed for some type of wild parsley, dill or fennel. Poison hemlock roots can be mistaken for parsnips, its leaves for parsley or fennel, and its roots and seeds for wild carrots or anise."

Poison hemlock, whose scientific name is Conium maculatum, is the plant from which juice was used by the ancient Greeks to kill Socrates. It typically grows in riparian areas, stream banks, canals and ditch banks and pastures. It is a biennial plant, meaning it grows for two years, flowers, seeds and then dies.

"It’s important for property owners to get involved in dealing with poison hemlock and other noxious weeds because Idaho law requires them to control noxious weeds on their lands. One of the best ways to control noxious weeds is to learn how to identify them on the lands you own or visit. But if you as a landowner or recreationalist are uncertain about whether you have poison hemlock growing on your property or need technical expertise to identify and eradicate this toxic noxious weed, please contact your county weed superintendent’s office or look in the yellow pages for a private weed control application company,” Batt added.


Poison hemlock. Photo courtesy of

Poison hemlock grows 3 to 6 feet tall with a smooth green stem, usually spotted or streaked with red or purple spots. The leaves are finely divided and lacy, resembling a “carrotlike” leaf. The weed has flowers that are small, white and clustered and resemble the spokes of an umbrella. The poison hemlock root is fleshy and white. When crushed, poison hemlock’s leaves and roots emit a rank, unpleasant odor often compared to that of a mouse or parsnip.


Though highly toxic, poison hemlock is very easy to control and eradicate with hand pulling and the use of broadleaf herbicide treatments. Always wear rubber gloves and protective clothing/gear when pulling this weed, and place the plant into a plastic bag and dispose of it into a trash receptacle. When using an herbicide to control and eradicate poison hemlock, officials say to use an approved registered herbicide and always follow the label and safety instructions on that label.

For more information about poison hemlock and the best ways to eradicate and control it, log on to the Idaho Weed Awareness Campaign’s website and click “Idaho’s Noxious Weeds” and then “Poison Hemlock.”

—From an Idaho Weed Awareness Campaign news release