By Katie Martin – Smith County Extension Agent
Do you ever see people arguing on social media? Maybe over politics or religion, maybe over something silly like music or sports. Do you immediately head to the comments to see what everyone is saying and decide who is right and who is wrong? Each year, in gardening pages I am part of, there is inevitably an argument over the identification of a plant someone thinks is poison hemlock. Sometimes it is, and sometimes it isn’t, but it always creates a spirited discussion! People are worried about this weed, and for good reason.
Poison Hemlock is a highly toxic plant that poses a significant risk to both humans and animals. It is sometimes referred to as deadly hemlock, spotted hemlock, or poison parsley, and can be found growing in cool-season grass pastures, roadsides, drainage ditches, and stream banks.
Poison Hemlock is recognizable due to its small, white flowers that form umbrella-shaped clusters, bright green and fern-like leaves, and smooth, hollow, stems which are marked with characteristic purple blotches or streaks. Mature plants typically grow to three to four feet tall. Queen Anne’s Lace or wild carrot is commonly mistaken for poison hemlock. However, their flower shapes differ and Queen Anne’s Lace does not share the purple streaking on the stems. Fortunately, Queen Anne’s Lace is not toxic.
Poison Hemlock is dangerous to grazing livestock, but thankfully deaths are rare due to the plant’s unpalatability. However, that changes after herbicide application. After spraying, the palatability increases, and animals are more likely to graze the plant. Livestock should be excluded from infested areas before applying herbicide. They should continue to be excluded until the plants have died and are brown and dry.
November or March to April are the ideal times for treatment. With thorough coverage that is achievable with spot sprays, products such as 2,4-D, Brash, GrazonNext HL, and Duracor are fairly effective. Before spraying, be sure to thoroughly read the herbicide label and follow all directions and precautions. Realize that plants that are growing upright and nearing the seed head stage will be very hard to kill with herbicides. Bush-hogging to prevent seed formation may be a better option.
For more information about poison hemlock or other weeds, go online to smith.tennessee.edu and check out our weed control page under the agriculture tab. There you can find fact sheets on Poison Hemlock and many other common weeds, as well as UT recommendations for control or contact the UT Extension office at 615-735-2900.
