How to recognize and fight poisonous hemlock | Home & Garden

URBANA – Poisonous hemlock (Conium maculatum) has received a lot of attention lately, with reports of nationwide population expansion and resulting increased human contact with this poisonous plant. However, there is some confusion about the risk this plant poses to humans and animals and what measures should be taken to protect it.

The wild carrot family (Apiaceae) has long been known to include plants with potentially harmful effects on humans. Many plants in this family, including poison hemlock, are dangerous or even deadly if eaten, and many produce other chemical defenses that have serious effects if we simply come into contact with parts of the plant.

Wild parsnip (Pastinaca sativa), another plant in the carrot family, is known for its photoreactive juice. Compounds in the juice called furanocoumarins cause a painful rash when the juice comes in contact with skin in the presence of sunlight. Every year, many people are unknowingly exposed to this plant, resulting in a mysterious skin rash. In my experience, it is the most common member of the wild carrot family that causes harm to humans.

The risk of developing a skin rash from exposure to poison hemlock varies depending on the health of the plants involved. It is possible to be exposed to sap and not get a rash, which has led to some confusion as to whether or not poison hemlock has the ability to cause rashes.

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Danger of swallowing poisonous hemlock

However, the risk of death from ingesting poison hemlock is not questioned. Another group of compounds produced by this plant, notably coniine and some other toxic alkaloids, cause rapid death in very small amounts if they enter the body through ingestion or otherwise.

This attribute has been somewhat sensationalized in recent years, attracting much media attention and creating a general panic surrounding exposure to poison hemlock. That’s not to say that precautions shouldn’t be taken around this poisonous plant, but it’s highly unlikely that death could result from being in the vicinity of poisonous hemlock plants alone.

Poison hemlock is a non-native, invasive plant commonly seen along fence lines and pasture edges, posing a serious threat to grazing animals. When eaten, the plant is just as deadly to livestock as it is to humans. It is not a preferred forage crop, however, and grazing animals usually prefer other higher quality plants to poison hemlock. However, action must be taken quickly when this plant occurs in or near pastures.

Where is poison hemlock found in Illinois?

While poison hemlock is certainly widespread in rural areas, it is less dangerous in more developed landscapes. The plant thrives on disturbances and occupies mainly degraded habitats.

It is unlikely to show up in your vegetable garden or landscaping.

It’s most likely along highways, railroads, field edges, and other areas that are rarely mowed.

How to control poison hemlock

Controlling poison hemlock is a bit tricky because the plant, like many others in the carrot family, is a biannual, meaning it will grow for two years before setting seed and dying. Control measures focus on stopping seed production, but vary depending on the life stage of the plants.

At this point in the season, chemical control is not a good option as the plant has started flowering and may be near seed set. However, it is an opportune time to hand pull or remove plants with a sharp shovel as plant resources are low due to the high investment required to flower and set the seeds. Use a sharp shovel to sever the taproot below the soil line. Or plants can be hand grown if soil moisture permits. Grown or cut plants must be bagged and sent to landfill as seed production can still take place.

Mowing is a good option to stop or limit seed production when other measures cannot be taken. Repeated mowing can actually eliminate the plant if applied consistently over multiple growing seasons. However, be sure to mow before seed production begins, otherwise your mower may spread seed to new locations the next time you mow.


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