Beware of hemlock for humans, animals


All I’m going to say this week regarding planting progress in Clinton County is… Rain, &%*#$# rain, go ahead!

Please pray for farmers who still have acres to plant this year. Oh yeah, while you’re at it, say “Thank you” to a farmer for all they do to help put food on our tables. It’s years like this that they need our support. This planting season has been stressful to say the least.

For the rest of my article this week, I want to focus on a weed seen throughout the county called poison hemlock. Hemlock is a member of the Apiaceae or parsley family, which also includes wild carrot (Queen Anne’s lace), wild parsnip, cow parsnip and giant hogweed.

Poison hemlock has been around in Ohio for a long time, and there are many areas where it never comes under any control measures, such as abandoned fields and woodlots. Other areas where poison hemlock can be found and seen include field edges, banks of ditches, roads, hay and pasture fields, etc.

These are areas where it could or should be controlled, particularly where it may pose a risk to quality or safety. Poison hemlock is toxic to animals and humans, but it is important to understand that poisoning only occurs when ingested.

For an animal, it has a strong odor and bad taste, so unless there is nothing else to eat, animals tend to leave it alone.

However, it can inadvertently end up in hay bales – where it retains its toxicity. For hemlock, the toxins will remain viable and deadly regardless of the drying process and methods of hay storage. All parts of the plant are poisonous, with the seed heads being the most poisonous.

For us humans, I wouldn’t eat any plant that I don’t really know what it is. Some accidental poisonings in the United States have occurred due to people mistaking poison hemlock for Queen Anne’s lace (wild carrot) in which the flowers can be eaten.

Poisonous hemlock contains eight piperidine alkaloids, with coniine (mature plants) and g-coniceine (young plants) being the two predominant toxic compounds. Experimental hemlock poisoning in cattle showed a wide range of clinical signs suggesting variation in the toxic alkaloid content of the plant.

Cattle eating as little as 300 grams up to 0.5% of their body weight have been shown to be fatal. Bluish discoloration of the skin due to poor circulation, respiratory paralysis, and coma without convulsions are common signs before death, which usually occur within 2-3 hours of consuming a lethal dose.

Contact with hemlock can also cause skin and eye problems that are far more likely than internal poisoning.

The severity of this response varies depending on the sensitivity of the individual and the degree of contact. This only occurs with direct contact with plant parts or plant fluids.

Anyone mowing or removing hemlock by hand should keep this in mind and protect themselves from skin and eye contact.

I’ve also read suggestions not to mow large populations of poison hemlock in an open tractor, as tiny plant parts or juices can become airborne and could be ingested, which could lead to poisoning.

Poison hemlock is a biennial weed. It spends the first year as a basal rosette and the second year as an upright, towering flowering plant that can grow 6 to 10 feet tall.

The leaves are alternate, pinnately compound, finely divided, toothed and shiny green. Stems are branched, waxy with purple spots, hollow between nodes and grooved.

It usually blooms from June to August, but this year it has already been blooming for a few weeks. The flowers occur in clusters of small, white, 5-petalled flowers in a loose, umbrella-shaped raceme 2 to 7 inches across. It has a fleshy taproot.

Poison hemlock is on Ohio’s noxious weed list. Therefore, it must be controlled before it grows large enough to pose a threat and before seed production occurs to prevent spread. Information on Ohio’s Noxious Weed Law can be found here:

Application of herbicides

At this time of year when these plants flower, set seed and die, it is not always possible to use chemicals to control them. The aim should be to get rid of existing plants by cutting, mowing or manual removal, and to limit the production and spread of seeds.

The most effective time for herbicide application is fall when plants are low-growing rosettes in their first year of growth, or early the following spring when plants are still small.

Suggested herbicides and their respective efficacy ratings can be found in Table 21 of the “Weed Control Guide for Ohio, Indiana, and Illinois,” which lists pasture and CRP herbicides.

There are other products labeled for roadsides, industrial areas, etc., but they will not be included in this guide.

There is an excellent article online at which has excellent images and does a good job presenting information on other species in the Apiaceae family or parsley, including identification. wild carrot (Queen Anne’s lace), wild parsnip, cow parsnip and giant hogweed.

As always, for more information or questions, please do not hesitate to contact me at [email protected] or contact our office at (937) 382-0901.

Tony Nye is the state coordinator of The Ohio State University’s Small Farm Extension Program and has been an OSU extension educator for agriculture and natural resources for more than 30 years, currently serving Clinton County and Miami Valley EERA.


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