Many farmers across the state have just made or will soon make their first hay of the season. While making hay, it is important for growers to notice and remove any poison hemlock from their hay or pasture fields.
Native to Europe, poison hemlock is an invasive weed that was introduced as an ornamental in the United States during the 1800s. It is potentially poisonous if ingested by livestock 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 College of Agriculture. "There are no state laws that mandate control of it by landowners or along rights-of-way areas."
The weed is often found along fencerows, roadways and other areas not used for cropland across most of Kentucky and the United States. However, in the past several years, its presence has increased across Kentucky and is now found more frequently in some hay and pasture fields.
If consumed, 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 more likely eat it if no other forage is available or when consumed through hay.
Poison hemlock is often confused with Queen Anne's lace, a non-toxic weed. Both plants produce leaves and clusters of small, white flowers that look somewhat similar. However, poison hemlock has smooth stems with purple spots throughout 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.
Ideally, growers 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. Since 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.