We’ve all heard the story of how Socrates was forced to drink a potion containing poison hemlock (Conium maculatum). All parts of it are toxic, and the plant is relatively common in many places including this region. Plants are deathly poisonous to livestock, pets and humans.
We have another lookalike to this toxic weed. Not only does water hemlock (Cicuta sp.) look like poison hemlock, it’s even more common and more toxic. All parts of the plant can kill you in as little as 15 minutes. According to several sources, it only takes a piece of root the size of a walnut to kill a 1200-pound cow or horse.
Both species strongly resemble Queen Anne’s Lace (Daucus carota), often called wild carrot. Wild carrot is a commonly used medicinal plant and is often found near the poison impostors. All are in the same plant family, as is wild parsnip (Pastinaca sativa), a common foraging herb. It can be confused with its poisonous relatives also.
Water hemlock, like the name implies, is usually found in wet places. Many ditches are full of it. It’s blooming right now as are most of its non-poisonous cousins. Plants are usually three to six feet tall, but I’ve seen some significantly taller.
Flowers grow in white circular clusters called umbels. Several small umbels make up a larger disc-shaped structure called an inflorescence. Leaves emerge from stems one at a time. They are what botanists call tri-pinnate, in that they branch three times and individual blades run three directions. Blades have toothed edges.
Most folks need not worry too much about water hemlock, since it generally grows in wet places they do not frequent. However, their pets might romp in thick patches of it. Furthermore, seed can be dispersed into places where livestock might consume it.
Killing it can be a little tricky. I’ve read where a combination of glyphosate and imazapyr can be effective. Both are non-selective, which means they kill whatever they hit. Both are also systemic. That means they kill the entire plant.
Finding herbicides that will kill water hemlock only solves one part of the problem. There are regulations concerning spraying pesticides in waterways. Contacting someone who knows the regulations is important or you might wind up in trouble.
There are guidelines that must be followed before spraying pesticides in or near water, particularly if there is risk to drinking water supplies or a neighbor’s property. Sometimes hiring a professional with proper licensing and liability insurance is a wise move.
Another problem with spraying water hemlock is that while plants are dying, palatability for livestock increases. Keeping pets and livestock from accessing treated areas is critical.
Now that I’ve thoroughly scared you, water hemlock is still used as a medicinal herb. Preparations can be made to control migraines, menstrual pain and intestinal worms. I wouldn’t recommend this to anyone under any conditions. Much safer options are available.
If I offend any herbalists out there, I’m sorry. Using water hemlock to treat any human or livestock ailments is insane. Even the slightest dosage miscalculation could be fatal.
good stand of water hemlock with a soybean backdrop
Water hemlock among the cattails
Water hemlock at the edge of the road
Ted Manzer teaches agriculture at Northeastern High School (tmanzer@ecpps.k12.nc.us).
tedmanzer 
It looks like you found a corndog orchard too, in the second picture from the bottom.
Poison hemlock is not very common here, but even where it is common, we have no problem controlling it reasonably well just by pulling up the big plants before they bloom. They do not seem to get established here.
The biggest problem here is that nobody knows what it is, so they don’t do anything about it and it spreads.
Because it does not spread as aggressively in our semi-arid climate, we could probably nearly eliminate it from urban and suburban areas if more people just got rid of it. I think that it will always live in small colonies in the few riparian areas. Tree huggers would want to protect it if there was too much effort put into eliminating it, just like the blue gum eucalyptus, pampas grass, and every other invasive plant.
Spot on.
LOL. I wrote Ted and asked him to write about this plant. I live on a tidal creek that I am planting with native flood-tolerant plants. This summer is the first time I have had water hemlock and I eradicated around 15 plants. I found the biggest before it set a flower and thought it was a pot plant! After noticing the hollow stem, I googled until I found it and was horrified by how dangerous it was. Because most of the Queen Anne’s Lace I see is while driving, I only notice the flower and not the leaves. I am willing to bet a lot of the “Queen Anne’s Lace” I have seen by ditches is actually water hemlock. I am very grateful that Ted chose to write about it because most people would reasonably assume it was Queen Anne’s Lace. Most people are not as familiar with plants as you and Ted.
We actually know it as Queen Anne’s lace! Oh my! However, everyone seems to know to get rid of it, and to not bring it in as cut flower.
I wrote about Queen Anne’s lace back in 2012 and included some pictures. From a distance the two might look similar, but up close nobody should confuse them. The problem is they often grow in close proximity, just like the meadow mushroom and the destroying angel. There’s no room for error.