WEST LAFAYETTE, Ind. — Crop and livestock producers with
poison hemlock in their pastures, crops or ditches should consider treating the
weed in the fall, a Purdue Extension weed specialist said.
Poison hemlock is a biennial weed that is toxic to both
livestock and humans, if enough is consumed. It can be identified by its finely
divided, toothed leaves and white flowers. Its stems are hairless, have purple
spots or blotches and can grow to 2 to 7 feet in height.
“The weed seems to be spreading, becoming a more common
occurrence in pastures, agronomic crops, fencerows and roadsides,” Bill Johnson
said. “It can be difficult to control in the spring. It’s easier to control in
the fall because it’s more sensitive to herbicides.”
The plant growth and appearance is more visible in the
spring, when the plants “bolt” or elongate rapidly and the white flowers bloom,
so that’s when most people become concerned with it. But Johnson said there is
active rosette formation of the weed in the fall.
“Growers should really think about fall-applied herbicide
treatments whether they’re treating their pastures or fields going to corn or
soybeans next year,” he said. “They should be treating them in the fall to
control poison hemlock.”
For control in grass pastures, he recommended using one of a
couple of herbicides that contain triclopyr as an active ingredient.
The good news for livestock producers is that while poison
hemlock is considered to be most toxic in the fall, livestock usually won’t eat
the plant if there are other options in the pasture.
“Cows won’t usually eat poison hemlock because this weed
doesn’t taste as good as the more desirable pasture species,” Johnson said. “But
if the pasture is limited in desirable forages, then there may be a situation
where the cows will get hungry enough to eat the plant.”
In corn or soybeans where poison hemlock is a nuisance,
growers can try an aggressive tillage program to disrupt it. If a herbicide is
needed for control in agronomic crops, Johnson recommended applying products
Farmers should be aware that some herbicides can damage
legumes or other desired vegetation, so they need to double-check labels before