Poison hemlock and livestock

By Ben Beckman
Extension offices of Lincoln-Logan-McPherson Counties
Have you noticed tall weeds with umbrella-like white flowers in pastures, ditch banks, and along the roadsides? It may be poison hemlock, a toxic plant to both people and livestock.
Poison hemlock is one of Nebraska’s top ten poisonous plants. It thrives in wet or moist soils along streams, roadsides, and pastures. Hemlock has distinctive fern-like leaves and purple spots on its stems. A biennial plant, it grows as a rosette in its first year and produces a stalk with white flowers in the second.
So, how can you manage this weed? Avoid overgrazing pastures containing hemlock. When there’s plenty of forage, animals will eat the healthy, palatable plants and avoid hemlock. However, if grass gets short, even unpalatable poisonous plants might be consumed. This includes turning hungry animals into fresh pastures with hemlock; desperate animals may eat the first green plant they encounter. Ensure plenty of water, salt, and minerals are always available. Animals deprived of these essentials may eat abnormally, increasing the risk of consuming hemlock. Just five pounds of foliage can be lethal for cows, and only two pounds can be deadly for horses.
Fortunately, hemlock is usually not palatable to most livestock. They won’t eat much unless it’s the only green plant around or if the plant has been altered. Do not attempt to control hemlock during the grazing season by mowing or spraying if the area will eventually contain livestock. These controls can increase its palatability, making it more likely for animals to consume enough to be poisoned. Instead, control poison hemlock in early spring or fall when animals are not in the pasture, or fence off large patches if necessary.  Options for herbicide control may include 2,4-D + Dicamba; Graslan L®; Chaparral®; Cimarron Plus®; DuraCor®; Escort XP®; and Streamline®