By Marcus T. McCartney

Right now, one of our most toxic weeds is thriving everywhere in Washington County. This weed can be seen growing along roadways, river and creek banks, fields and pastures, fence rows, urban settings, and parks. Poison Hemlock is a noxious weed in Ohio, meaning this weed is regulated by Ohio State law and should be destroyed or eradicated if found on your property. All parts of this plant are poisonous to humans and livestock, so it is important to know how to identify and to properly remove and destroy it. Poison Hemlock is a biennial, meaning its life span is two years. During the first year (vegetative growth), leafy rosette form extending upwards of two feet. During the s year’s growth is when the plant shoots up its tall reproductive shoot (stem) with flowers.

It Can Kill

Poison hemlock is highly toxic to humans and livestock when ingested — either in its vegetative stage or when dried. As the tale goes, this plant was used to poison and execute the Greek philosopher Socrates after he was found guilty of corrupting the minds of young Athenians and for not believing in the gods of the state.

Typically, grazing animals will avoid poison hemlock because of its unpalatable taste, unless there is little other feed or forages available or when it’s consumed through hay.

When consumed, poisoning symptoms appear rather quickly which includes: bloody feces, vomiting, paralysis, trembling, loss of coordination, pupil dilation, coma and eventually death from respiratory failure.

Also, caution should be taken when handling the plant. The sap (juices) can cause toxic reactions in humans, resulting in a red irritating skin rash.

What does it look like

The first step to controlling poison hemlock is being able to recognize the plant. Right now, is a great time to identify the plant, because currently it is somewhere between 2 to 5 feet — with the potential to reach heights of 10 to 12 feet in moist conditions.

The leaves are dark glossy green, fern-like, triangular, and 3-4 times pinnately compound (Fig. #1). Probably the most identifiable characteristic is the plant’s smooth hairless purple-spotted stem (Fig. #2). The stem is also hollow between the nodes (where the leaves attach to the stem).

The plant’s flowers are small, white, and found in umbel-shaped clusters (Fig. #3). In Washington County, the plant will begin to flower around mid-May.

How To Control Poison Hemlock

Poison hemlock can be controlled quite easily, either by mechanical (organic) or chemically.

Mechanical Control (organic): Since poison hemlock is a biennial, it wants to die after flower pollination, therefore the plant does not store any energy in its reserves for later use. It takes up for six weeks for the seeds to become viable. About a week after the plant has flowered, simply chop it down at the base while wearing gloves, and either discard it away humans and livestock or throw it away in the trash. No regrowth will occur at this time because there are not any plant reserves in its roots. This will end seed production. Of course, if this plant has been present on your property for a while, it may take you up to 3-5 years to completely eradicate and exhaust the soil’s seed bank. Poison Hemlock seeds are only viable for 3-5 years.

Chemical Control: According to the Ohio State University Weed Control Guide, Crossbow and Remedy Ultra has the best rating for controlling poison hemlock, followed by glyphosate (Roundup), dicamba, and Cimarron Max. The plant can be sprayed anytime, but best results occur when the plant is small. Remember when applying chemicals, the applicator should wear proper PPE (personal protective equipment) and follow the label accordingly.

If you think you have poison hemlock on your property and need help identifying it, please call the OSU Extension office for assistance: 740-376-7431.

Marcus McCartney is the OSU Extension Agriculture and Natural Resources Educator for Washington County. He has been with extension since 2014. Marcus received both his bachelor’s and master’s degrees from West Virginia University.