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OSU Extension

College of Food, Agricultural, and Environmental Sciences

May 14, 2024 - 9:15am --

Two common weed questions we get this time of year concern poison hemlock and “that yellow weed in my fields” which is cressleaf groundsel.  Both species are poisonous to livestock and can present a challenge to control.  We should be cautious when we do discuss plants that are poisonous to livestock.  Typical control measures will also remove beneficial legume species.  Sporadic plants within a pasture, hay field, or fence row usually are not a problem.  Livestock will ignore these plants and preferentially chose to consume the more palatable species in the field.  It is when pastures become overgrazed, or weed populations become too high, that our concern elevates, and control becomes more important.  As always, a well-managed pasture and hay field will be your best friend for weed control.

Specifically, Poison Hemlock is a biennial weed from the carrot family that will be frequently found in fence rows, road ditches, and pasture and hay fields. Once the seed germinates, it will remain a small plant during the first summer.  After overwintering it will re-emerge and grow into an initial rosette by early March.  Usually in June, it will be bolting, then flowering and seed set. 

Studies: Harmful to horses, cattle

It is often confused with wild carrot, wild parsnip, spotted waterhemlock, and purple stemmed angelica.  The plant has a hairless, hollow main stem with purple blotches/spots.  Poison Hemlock contains several pyridine alkaloids which makes all parts of the plant potentially toxic, but the mature seeds are the most poisonous.  Studies have shown toxicosis in horses and cattle when they consume 2.5 to 5 lbs of plant material per 1000 lbs of animal body weight.  Muscle paralysis and suffocation are the typical signs of a significant poisoning.

Cressleaf groundsel is a member of the aster family and has daisy-like blooms.  Their upright, hollow, stem will have a purple hue.  They are a winter annual, with seeds germinating in the fall and flowering occurring the following spring.  Plant populations can quickly increase when not controlled.  Although studies indicating specific consumption amounts that relate to toxicosis haven’t been performed, affected animals may exhibit weight loss, unthriftiness, poor hair coat, anorexia, behavioral changes, sunscald, aimless walking, diarrhea, jaundice, liver damage, and possibly death.  Drying or ensiling the plants does not reduce their toxicity.  Cressleaf groundsel is most often confused with yellow rocket.

As both species are broadleafs, any of our traditional broadleaf herbicide products will be effective for an early spring or late fall application.  Products such as 2,4D or crossbow are very effective, as are the general contact herbicides like glyphosate or glufonisate.  Early season brush mowing can slow the plants spread, but this should be done just as the plant is flowering and prior to seed set.  In heavy infestations, if mowing is the preferred control option, it may be necessary to remove the plant residue from the field and composting or other disposal method.

H2Ohio program sign-up

There is still time to sign up for the newly expanded H2Ohio program.  The original program was first initiated in northwest Ohio and was recently expanded to cover the entire state.  Sponsored by the Ohio Department of Agriculture, the H2Ohio program is designed to reduce nutrient runoff by incentivizing producers to implement certain best management practices on their farm.  Eligible producers can enroll acreage into a Voluntary Nutrient Management Plan to earn $10 per acre.  Producers can also earn incentives of $10 per acre or $15 per acre for implementation of the plan and utilization of practices such as variable rate nutrient applications.  To learn more about this program, or to sign up, you should contact the Wayne County Soil and Water office.  The enrollment deadline is May 31st, 2024.

As spring planting and early season forage harvesting progress, I want to continue to wish you a safe and productive season.  We will continue to have some programming options throughout the summer months, so be watchful for those announcements.  As always, if you have any management or farm business questions, don’t hesitate to give me a call at the OSU Extension – Wayne County office.  Our phone number is 330-264-8722 and my email is

John Yost is an Extension Educator IV, Agriculture and Natural Resources, at OSU Extension-Wayne County
This article was previously published in The Daily Record.