The Enemy - Poison hemlock (Conium maculatum) is a biennial plant that grows up to 12 foot tall. This is the most toxic of Idaho's 57 listed noxious weeds. All parts of this plant are poisonous to livestock and humans, in fact the extract of this plant was use to execute Socrates of ancient Greece. The plant hosts white flowers (don’t mistake this plant for wild parsley). This plant is easy to distinguish as the stems have a purple striping up and down them that the other plants do. The leaves are fern-like and pinnately divided. The thick white taproot, which when sliced onto resembles walls with hollow chambers.
The Strategy - This plant inhabits the riparian areas along streams and ditches or even where there are sub-waters near roadways. It can become very thick once the plants become established. As the plant matures it blocks out sunlight and robs the soil of valuable nutrients and water. Wildlife cannot travel through the bamboo like stems (although they don’t turn woody) and obviously little or no animals can feed on it to help control it.
The Defense - There is one insect, a moth, that defoliates this plant. Mechanically digging up the plants can be effective in the first few years of establishment. Be sure to wear rubber gloves and protective clothing when handling this poisonous plant.
Opensight at 3.3 oz when plants are young. Click to view label.
Click for general recommendations on Dow AgroSciences Herbicides.
For technical information on use of Dow AgroSciences herbicides to control of invasive noxious weeds click here.
Click here for more technical information on use of Dow AgroSciences herbicides to control of invasive noxious weeds.
For information about Opensight click here.
Herbicides such as Escort® XP, Telar® XP, 2,4-D and Amine are best, but remember not to get the products inside the ditch banks, unless you're using an aquatically approved herbicide. Treatments in early spring are best, but these products can be used right up to a late bloom stage of the plant.
ERADICATING POISON HEMLOCK
PLEASE NOTE - The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.
For more information, click on the link below to download the Idaho's Noxious Weeds Control Guidelines publication produced by the University of Idaho Extension.
U of I Idaho's Noxious Weeds Control Guidelines (183 KB PDF download)