The rosette stage of the poison hemlock, very similar to what people would see now. Unfortunately, most people do not notice the weed until it is at least 3 or 4 feet tall with flowers on it. Photo by Jeff Burbrink.

By Jeff Burbrink
Ag & Natural Resources Extension Educator, Purdue Extension LaGrange

LAGRANGE — The winter of 2024 has been pretty much a bust. The warm temperatures have triggered some plants to begin waking up a little earlier than we are used to seeing here in northern Indiana. Our winter wheat, for example, seemed to green up significantly last week.

Jeff Burbrink

One other plant that woke up is poison hemlock, a member of the parsley family. Chances are, if you have acreage with fence lines, ditch banks, infrequently mowed road frontage, the edges of wooded areas or abutting a railroad, you have had it on your property for a while. Poison hemlock is a non-native invasive species. It is a biennial, mean it grows over two seasons before it goes to seed and dies.

Right now, you would find it as a low growing rosette, and its fairly easy to control. The newly greened rosettes are fairly easy to spot mixed in with the tans and browns of last year’s dead herbaceous plant material.

Later in the summer, it will send up a stalk that is 3-10 feet tall, with a stem that is stout, smooth and has distinctive purple blotches. The white umbrella like flowers will produce 1,000s of seeds. Flowering is when most people notice the issue, but control is very difficult at that point.

As the name implies, the plant is poisonous and can irritate the skin. Cattle and other grazers are sometimes poisoned when it gets baled into hay. The hollow stem, if used as a pea shooter, has been found to poison ornery little children.

Digging up individual plants is a very effective control for small areas. Be sure to wear gloves, long pants and long sleeves, and eye protection to protect from skin irritation. Mowing or cutting can be effective but will need to be repeated numerous times because the taproot stores a lot of energy and will simply send up new shoots for a while.

For larger patches of poison hemlock, herbicides are probably most effective. Glyphosate mixed at the 2% rate is fairly effective in areas where it is ok to burn down all the other plants in the area. If the hemlock is intermixing with grasses, broadleaf herbicides containing 2,4-D, dicamba and triclopyr work well.

For more information including pictures of various stages of the plant, visit tinyurl.com/yjxkekyp or tinyurl.com/yv2dz6jf

A leaflet that has been detached from a rosette. Note the parsley-like look to the leaf. Some people might describe it as fernlike at this stage. Photo by Jeff Burbrink.