Ask the Vet

Poison Hemlock an Invasive Issue

Most common in moist areas along fencerows, roads and other areas not used frequently, poison hemlock can be a danger if eaten in enough quantity. (Photo by Thinkstock/istock)

Question: My husband wants to know more about poison hemlock and if it can be a problem for livestock. He says it is new here in southern Indiana and is beginning to be everywhere -- in hay fields, grain fields, also in hay, corn, silage and haylage. He has tried to eradicate it but others don't, and when it goes to seed it just gets carried right back into our fields.

Answer: Poison hemlock is extremely toxic. Humans can develop symptoms just by handling the plant. This is, after all, the same plant used to kill Socrates in ancient Greece. But like many toxic plants, it rarely causes problems in well-managed herds.

Our livestock are usually smart enough not to eat it. Hungry livestock are the ones most likely to consume toxic plants. In Alabama, for example, most farms have Perilla Mint, Bracken Fern, Mountain Laurel and a variety of other toxic plants, but we rarely see problems with them.

Poison hemlock remains very toxic when dried, so the danger to livestock is much greater when it's incorporated into hay and other stored feeds.

An invasive species, poison hemlock was introduced from Europe as an ornamental. It is most common in moist areas along fencerows, roadways and other areas not used for cropland or pasture. It is often confused with Queen Anne's Lace, a non-toxic, lovely late-spring wild flower/weed. Poison hemlock typically blooms earlier, can get much taller and has smooth stems while Queen Anne's Lace has fuzzy stems.

Signs of poisoning include nervousness, trembling, muscle weakness, loss of coordination, pupil dilation, coma and eventually death from respiratory failure.

A variety of herbicides including 2, 4 D do a good job of controlling poison hemlock in its vegetative state. Mowing prior to flowering can prevent seed production.

Even though the chance of poisoning in your herd is low, your concerns about this very toxic plant are legitimate. I would work very hard at eliminating it from your property and try to make others around you aware of its toxic potential and get them to coordinate in your eradication efforts.