Late winter scouting can help battle a poisonous weed

Poison hemlock header
(Photos: MU Extension)

AVA, Mo. — With spring on the horizon, it is time to scout fields for early emerging weeds. According to Ben Polley, an agronomy graduate student working for University of Missouri Extension, many of the weeds start greening up before the rest of the field.

“One weed that is particularly easy to find this time of year is poison hemlock. It presents as a bright green rosette that, once you know what it looks like, is easy to identify,” said Polley.

poison hemlock leaves
Poison hemlock has a smooth, hollow stem covered in purple splotches and compound leaves with many very small leaflets. All parts of the plant are toxic to both humans and livestock. (Photo: MU Extension)

Identify it

Poison hemlock is a biennial plant that has smooth, hollow stems covered in purple splotches. It has compound leaves with many very small leaflets. It has white flowers that grow in clusters that resemble umbrellas. These closely resemble the flowers on Queen Anne’s Lace.


Poison hemlock is aptly named. All parts of the plant contain toxic alkaloids that can cause salivation, vomiting, diarrhea, weakness, paralysis, nervousness, trembling, dilation of pupils, weak pulse, convulsions and coma. Poison hemlock can rapidly take over an area, out competing other plants and creating a sea of poisonous plants, said Polley.

Weed removal

It is important to gain control over poison hemlock as early in the season as possible. In small infestations, physically removing the rosettes in late winter or early spring can be effective. They can be dug out much like dandelions. Due to weather conditions, it is often possible to physically remove them earlier in the season than it is to kill them with herbicides.

poison hemlock in bloom
Poison hemlock is a biennial plant that closely resembles Queen Anne’s Lace when in bloom. Early removal is key to getting ahead of this invasive species. (Photo: MU Extension)

Physically removing mature plants could be dangerous as all parts of the plant are poisonous, including the sap, said Polley. “People should take caution not to get it in their eyes or mouth or on their skin.” There are a number of herbicides on the market that can be used to control poison hemlock. Remember to always read the label and follow all instructions when working with herbicides.

“Do not attempt to use grazing to control this weed,” said Polley. The plant’s odor will deter most animals if they have adequate forage available, but it’s also toxic. “Hungry, and especially young, animals may be tempted to consume the bright green leaves, much to their detriment, and possibly yours,” said Polley.

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