LINCOLN, Neb. — Have you noticed tall weeds with umbrella-like white flowers in pastures, ditchbanks and along the roadsides? It may be poison hemlock and be careful, as it is poisonous to livestock and people.
Poison hemlock is on the list of top 10 poisonous plants here in Nebraska. This weed can be found throughout the state, especially in wet or moist soils along streams, roadsides and pastures. Hemlock has fern-like leaves with purple spots on the stems. Poison hemlock is a biennial broadleaf plant, meaning it will grow as a rosette its first year and produce a stalk with white flowers in its second year of growth. They have taken off growing around the state with the recent much needed rain.
So how can you manage this weed?
It’s critical that you avoid overgrazing pastures that contain hemlock. When adequate forage is available to graze, animals select healthy, palatable plants to eat and avoid the hemlock. But if grass gets short, even unpalatable poisonous plants might be eaten. This includes turning hungry animals out into fresh pastures containing hemlock — some hungry animals will eat the first green plant they come to, palatable or not.
Be sure plenty of water, salt and mineral are always available, as animals deprived of water or mineral may eat abnormally, increasing the risk of consuming some hemlock. Consuming just five pounds of foliage can be potentially lethal for cows, while just two pounds can be deadly for horses.
Fortunately, hemlock usually is not palatable to most livestock. Animals won’t eat much of it unless it is the only green plant around or if the plant has been altered in some way. Do not — and I repeat, do not — try to control hemlock during the grazing season by mowing or spraying with 2,4-D + Dicamba. This alters the plant and can actually increase its palatability, making it more likely animals will eat enough of it to cause poisoning. Instead, control poison hemlock in the early spring or fall when animals are not in the pasture or fence off large patches from livestock if control is necessary.
— Melissa Bartels, Extension Educator, University of Nebraska-Lincoln