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Our first run-in with water hemlock

This summer during haying my son noticed a questionable weed in the field he and his father were haying. We have been reading our Edible and Medicinal Plants of Canada book a lot this summer trying to identify many wild flowers growing in our area we have never seen before.

This turned out to be a good use of time since he was able to immediately spot outcroppings of a plant that looked suspiciously like water hemlock. There is also a weed in our area that again is non-poisonous cow parsnips (Heracleum maximum) which is what most of the locals believe this weed to be.

To be safe we conferred with the local Manitoba Agriculture, Food and Rural Initiatives office to get a positive identification of our hemlock and were unpleasantly surprised to find out we were right. We in fact are growing a bumper crop of this weed. Their recommendation was to cease all use of this land till we can eradicate the hemlock.


The next question had to be “So how poisonous is it?” Rhubarb leaves for example are poisonous but a 145-pound mammal has to eat 11 pounds to die. But considering I remembered learning that Socrates committed suicide by drinking a glass of hemlock I encouraged my husband this plant deserved further research. We learned one root can kill a 1,600-pound cow and that all parts of the plant are toxic. Proper identification is crucial.

Water hemlock has narrow leaves with sharp tooth-like margins. The flowers are small, white and in umbrella-like clusters. The roots are very bulbous, which distinguishes it from look-alike plants such as cow parsnip, which also has narrow leaves, but lacks tooth-like margins and bulbous roots.

Cow parsnip is also very common in our area, but it is generally a larger plant and has very large fan-like leaves. In drier conditions, cattle and other livestock can graze cow parsnip and it actually has good feed value. In fact, there are areas where cow parsnips are harvested for silage and the cows have a greater milk yield then cows fed on clover and timothy grass silage. The cow parsnip silage also provides a higher amount of digestible protein, volatile fatty acid, and cellulolytic activity and carotene values.

Water hemlock on the other hand cannot be fed. It is deadly fresh or in dried hay. When ingested, it attacks the central nervous system of the animal. Salivation and frothing at the mouth are often the first signs of poisoning. This is promptly followed by muscle twitching, seizures, coma and death. It is also associated with cattle birth defects and can pass in the milk of an animal. Although there is some documentation that the poisons dissipate, the longer it is dried there is no real data to show when it is safe to use. This is also a very deadly plant for humans. All parts of the plant are poisonous and it closely resembles wild caraway so if it is in an area people should be very careful. Even ingesting a small part of the root can be fatal.

Livestock poisonings from water hemlock generally occur in the early spring when cattle eat the young shoots, which appear before much else is growing. Hemlock likes wetter conditions so is often found around dugouts, streams and other water sources. It generally does not like a lot of shade so is often in the open. Apparently a lot of the toxins found in the rest of the plant during the other parts of the year are more concentrated in the root in the fall. Therefore the late fall — when other vegetation is sparse — is another critical time when poisonings occur from eating the bulbous roots. The plant in its entirety can be pulled out easily which is how livestock, especially cattle, gain access to the roots.


Our farm pastures have not been contaminated but hayland has. Since one plant can produce 30,000 seeds that remain viable for three to six years, and it reproduces solely by seed, this will make eradication interesting.

The recommendation from the agriculture people is to plough it under this fall so that the plants rot. At this time it is clearly visible due to the white flowers/seed heads and it is quite tall. In the spring, once the area greens up, we are supposed to disc it lightly. The idea is to kill what might have grown without disturbing seeds which should be far enough underground as to not germinate. Then they said to reseed the area to hay and we should be fine. What we may do is cover the area with rotted manure then disc further reassuring ourselves that we aren’t just replanting this weed.

This will be our course of action along with having to purchase replacement hay from an area that is not having a sudden problem with the weed.

This problem made me think of stories my Gran told me as a child about her husband walking his fields in the evening after supper to pull offensive plants. Maybe we all need to be spending a bit more time getting reacquainted with our land since we must have had this weed for a few years and never noticed it till it was a large problem.

— Debbie Chikousky farms with her family at Narcisse, Man. Visitors are always welcome. This article appeared in the Oct. 7, 2013 edition of Grainews (page 46).

CLICK HERE to read Dr. Roy Lewis’ column on water hemlock, and its risks to cattle, also from the Oct. 7 issue of Grainews.


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