Remove Poison Hemlock From Forage

The invasive weed poison hemlock can be fatal to livestock, so take care to remove it from pastures and hay.

by Dani Yokhna
Poison hemlock
Courtesy Oregon State University/
Clint Shock

Poison hemlock is an invasive weed that is poisonous to livestock when ingested, so keep it out of your hay and pastures.

Many farmers across the country are in the midst of making their first hay of the season. While making hay, it’s important for farmers to notice and remove traces of poison hemlock from their hay or pasture fields.

Native to Europe, poison hemlock is an invasive weed that was introduced as an ornamental plant in the United States during the 1800s. Poison hemlock is potentially poisonous if ingested by livestock (such as goats) or humans in both its vegetative growth stages and when dry.

“This is a classic example of one invasive plant problem that has gotten out of hand, but people may not be as alarmed about it as with other invasive plants because they may not know what it is,” said J. D. Green, extension weed scientist with the University of Kentucky’s College of Agriculture. “There are no state laws that mandate control of it by landowners or along rights-of-way areas.”

Poison hemlock is often found along fencerows, roadways and other areas not used for cropland across the United States. However, in the past several years, poison hemlock’s presence has increased and is now found more frequently in some hay and pasture fields.

If consumed, poison hemlock’s poisoning symptoms appear rather quickly and include nervousness, trembling, muscle weakness, loss of coordination, pupil dilation, coma and eventually death from respiratory failure. While livestock typically refrain from eating poison hemlock in its natural growing state because of its unpalatable taste, they will eat it if no other forage is available or when consuming hay.

Poison hemlock is often confused with Queen Anne’s lace, a nontoxic wildflower. Both plants produce leaves and clusters of small, white flowers that look somewhat similar. However, poison hemlock has smooth stems with purple spots while Queen Anne’s lace has hair along its stem and leaf bases. Peak bloom for poison hemlock is in late May and early June, whereas Queen Anne’s Lace is just beginning to produce flowers at that time.

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Ideally, farmers can control poison hemlock with herbicide products, such as 2, 4-D, applied during the plant’s vegetative growth stage in the late winter or early spring or with an herbicide treatment in the fall. Because it’s too late this season to make an application and the plants are in full bloom, growers can still control poison hemlock by mowing the plant before it produces new seeds, which occurs soon after flowering.

Forage producers who find poison hemlock in their fields will want to either mow around the weed when cutting hay or mow and separate it from the other forages.

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