Typical roadside area with poison hemlock in Elkhart County on April 15. If using herbicide, now is the time to treat this very dangerous plant for best control. Photo provided by Mark Evans.

By Mark Evans
Ag & Natural Resources Plant and Soil Science Extension Educator, Purdue Extension Elkhart County

GOSHEN — Introduced from Europe as an ornamental plant, poison hemlock contains highly poisonous alkaloid compounds that can be fatal to humans and animals. It is commonly found along roadsides, streams, trails, ditches and abandoned unkept areas.

Mark Evans

This plant spreads via seeds, so interrupting the development of new seed formation, while also exhausting the existing seed bank in the soil from previous years, is the key to success over the long term.

Keep in mind that all parts of this plant are poisonous. This includes the pollen that forms on the plant flowers in June which can make one sick or even be lethal if chopping down plants and breathing pollen.

Control when the plant is young is key. The easiest way in many cases is to mow areas where there is an infestation of the plant. Often mowing spreads the plant when mowing after it has gone to seed. The seed and pollen may be very concentrated with the toxin so care should be taken to not be working or playing in areas where these plants dominate. Mowing will need to be repeated until July keeping the plant from entering the reproductive stages of growth.

For chemical control it is essential to start now when plants are young for best control. A nonselective option for areas inundated with poison hemlock would be at least a 41% concentration of glyphosate mixed as a 2% solution.

For a hand pump sprayer, mix 3 ounces of glyphosate with one gallon of water. For best control, spray in the morning and if possible, use soft water that won’t tie up the chemical like extremely hard water.

For most areas where there are also grasses and other plants with the poison hemlock, use 2,4-D or triclopyr which are selective options that will only kill broadleaf plants like poison hemlock while not having an impact on the grass species.

Follow the label instruction for these broadleaf herbicides that may have varying formulations. Herbicides are most effective on young first year rosettes or very small second year plants. Search out these plants now and treat before they bolt with growth in the coming weeks with warmer weather.

For more information check out Purdue Extension’s Invasive Plant series publication FNR-437-W or you may request a printed copy or emailed copy by calling the Purdue Extension Elkhart County office at (574) 533-0554.

Close up view of young poison hemlock along Elkhart County roadside on April 15. If using herbicide, now is the time to treat this very dangerous plant. Photo by Mark Evans.