How to get rid of poison hemlock for good

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(Photo: Jan Samanek, State Phytosanitary Administration, Bugwood.org)You’ll find poison hemlock along fencelines and ditches around this time in Ohio, and it’s a weed livestock owners cannot afford to ignore because all parts of this plant, including leaves, stems and roots, are poisonous when ingested.

I thought poison hemlock awareness was increasing significantly, but then reality hit me.

While driving back from Cincinnati to Marietta, with my family, we stop to explore the Serpent Mound in Peebles, Ohio. While making our way there, we saw a farm selling hay, so I stopped to ask how much since I was running low this year due to the lack of forage production at the beginning of the growing season.

As I was pulling up to the house, I couldn’t help but notice all the 1-foot poison hemlock plants, so I jokingly asked the farmer if he was in the business of growing poison hemlock or milking cows.

He quickly replied, “Well, I guess both.”

After pointing it out and describing the effects to him, he mentioned that his cows were “acting funny” the other day and thought they got into something. He had no idea this invasive plant was on his farm and quite frankly, never gave it much thought.

It can kill

Poison hemlock is highly toxic to humans and livestock when ingested — either in its vegetative growth stage and when dried.

Typically, grazing animals will avoid poison hemlock because of its unpalatable taste unless there is little other feed or forages available or when it’s consumed through hay.

When consumed, poisoning symptoms appear rather quickly which includes: bloody feces, vomiting, paralysis, trembling, loss of coordination, pupil dilation, coma and eventually death from respiratory failure.

How to control

Poison hemlock can be controlled quite easily. I completely eradicated it from my farm in two years using nothing but a machete, a little patience and botany.

In the summer of 2015, the county township asked if they could spread soil along my property to help build-up and stabilize the road since the road was 4-5 feet higher than my pasture.

At the time, I said yes, but I did not realize the soil source came from road ditches that the county had been clearing.

When spring of 2016 rolled around, the amount of junk weeds that appeared along my property was heartbreaking, and, of course, poison hemlock was among the junk weeds.

Since poison hemlock is a biennial (a plant that takes two years to grow from seed to fruition and die — this is where botany comes in to play), I used a little patience and waited for the plant to flower.

One week after the plants flowered, I simply chopped them down at the base and discarded the plants over the hill and away from livestock. By cutting the plant down after flowering, I eliminated its potential to produce more seeds.

At this time, the plants did not have enough reserves to shoot up another flowering stalk.

In the spring of 2017, I had a few more plants bolt up (leftover 2015 seeds that germinated in 2016), so I simply repeated what I did the year before to control it.

Now in 2018, I did not have a single plant bolt up and all it took was patience, botany and a machete.

Of course, if this plant has been present on your property for a while, it may take you up to 3-5 years to completely eradicate and exhaust the soil’s seed bank. Poison hemlock seeds are viable for only 3-5 years.

What does it look like

The first step to controlling poison hemlock is being able to recognize the plant. Right now is a great time to identify the plant, because currently, poison hemlock is somewhere between 2 to 5 feet — with the potential to reach heights of 10 to 12 feet in moist conditions.

Leaves are dark glossy green, fern-like, triangular, and 3-4 times pinnately compound (as shown in the picture). Probably the most distinguishing feature is the plant’s smooth hairless purple-spotted stem, which is hollow between the nodes.

Once the plants start to flower, they will be small, white, and found in umbrella-shaped clusters.

Looks like wild carrot

Sometimes poison hemlock gets confused with wild carrot (a.k.a.: lace flower, Queen Anne’s lace). However, wild carrot has hairs along its slender stem and leaf bases while poison hemlock’s stem is smooth and purple-spotted.

Peak bloom for poison hemlock is in late May and early June, whereas wild carrot is just beginning to produce flowers. Wild carrot will only reach heights of 3 feet or less.

Also, poison hemlock is more branch-like than wild carrot.

Take action

Once poison hemlock is successfully recognized and confirmed, the next step is to take action to control it.

Besides using my method of mechanically controlling the plant (hand-pulling, whacking, cutting, mowing, etc.) chemical control is also a viable option. Since poison hemlock is a biennial, it is best to control first-year plants by applying herbicides in the fall, and for second-year plants, applying herbicides in the spring before the plant gets too large.

According to the Ohio State University Weed Control Guide, Crossbow and Remedy Ultra has the best rating for controlling poison hemlock (rating of 9) followed by glyphosate (Roundup), dicamba, and Cimarron Max, which all have a rating of 8.

It is important to note that these herbicides are either broadleaf killers (including legumes) or nonselective (kills both grasses and legumes). For light infestations, spot treatment may be the preferred method.

Remember, poison hemlock is one of Ohio’s 21 noxious weeds and should be controlled.

For more information on poison hemlock or help with identifying it, contact your local Extension office.

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Marcus McCartney is an OSU Extension agriculture and natural resources educator in Washington County. Send questions or comments to Mccartney.138@osu.edu or write c/o Farm and Dairy, P.O. Box 38, Salem OH 44460.

12 COMMENTS

  1. Why wait to flower? We have an acre and this hemlock was introduced with a load of soil. we have been having a hard time getting rid of it. We try not to use chemicals, but wow. For homeowner keeping on top of this has been tough.
    Thanks,
    Linda

  2. Hi Linda, Typically when doing mechanical control, like chopping a plant down, if you chop it early, before it flowers, it still has plenty of energy in the root to send up a shoot (albeit usually shorter) and then flower and go to seed. If you chop it after it has flowered, often, as Marcus wrote in his article, it won’t have the energy to recover at that point in its life-cycle, and you won’t see it sprouting back up and setting seed.

  3. What about mowing them down vs machete? I would mow to the middle and gather and dispose of, as well as clean mover so as not to spread to the rest of the property.
    Thank you,
    Liz

  4. Yes – you can mow them down but keep in mind, if you mow them down now, you’ll have to make multiple mowings because the plant should have enough energy in its taproot to shoot up another reproductive stalk. Keep monitoring the site for regrowth and cut/mow as needed. Th goal with mowing is not let the plant develop flowers.

    • TWO YEARS AGO, I READ IN THE “EAST COAST EQUESTRIAN” TO DRESS LIKE YOUR RIPPING OUT POISON IVY. HAT,PROTECTIVE EYEWEAR,GLOVES,MASK,LONG SLEEVE SHIRT, LONG PANTS AND APPROPRIATE FOOTWEAR.

  5. Just be careful not to get the sap/juices on your skin and definitely do not ingest it. Covering your skin and wearing gloves is recommended.

  6. We’ve been digging up the plants and getting most of the root on the big ones. So since it is a bi-annual, does that mean any small pieces of the root that break off will not regrow?

    • I shouldn’t regrow but this depends on the time of year you are digging it up and the stage of plant growth.

  7. I have noticed poison hemlock spreading everywhere on my 40 acres. I have used Roundup and it comes back. I’ve pulled it out in one meadow…but it’s back. I bought a flame thrower. Can’t use it on poison ivy because the flame vaporizes the poison and humans can then breath in the poison. Would torching the hemlock be the same risk? I also can cut and gather the cuttings with my leaf picker upper on the flat portions of my property but it is in the ravine and woods where I can’t take the mower. …and then, what does one do with the piles of cuttings? I hate using Roundup and other chemicals…

    Thank you for any help

    • Laurie and Brian,

      The plants keeps coming back due to new plant seeds germinating. For an area to be completely eradicated of Poison Hemlock, the soil’s seedbank needs to be exhausted. A weakness of poison hemlock is a short viable seed life; around 5 years – relatively short compared to other plants which can be up to 30 years or longer. Seeds which germinated this season, will be forming rosettes close to the ground. These rosettes can be sprayed with an effective herbicide; killing the plant and creating no bolting situation the following season. Or, wait until next season to cut it down when the plant has bolted and flowered to control it. Again, it will take up to 5 years or so to completed eradicate the soil seedbank; especially if it has been allowed to buildup.

  8. Laurie, it’s coming back because seeds are still in the soil. In theory you should be able to eradicate a biennial by taking care of it for two successive years. But there are always exceptions with seeds that take longer to grow. Keep at it and you will be successful. My late brother in law had loads of soil delivered and spread over a new septic bed. When I moved to help my sister after he died, I found a forest of 8-10 foot tall blooming plants.

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