Poison Hemlock
Poison Hemlock - Conium maculatum - is a tall (up to 2m) riparian herb found along the margins of watercourses in the UK. It is poisonous to humans and all livestock. There is a risk of fatalities to livestock once the plant has been cut as chemicals released by live plants which deter ingestion are no longer produced and animals are often attracted to the dead plant material as a source of ‘hay’.
Poison Hemlock has white flowers which resemble cow parsley. The definitive feature of this plant are the light green smooth stems and distinctive purple-red spots on the stem. Leaves can be up to 30 cm long and have coarsely toothed edges. The plant can grow very tall, up to 2.5 m in favourable places. It grows mainly in damp places along river margins but also on waste ground. It can often be seen along the hard shoulder and central reservations of motorways. The stems have characteristic purple-red spots and are smooth (unlike cow-parsley). The leaves are much more finely dissected than cow-parsley.
Cattle, goats, horses, pigs, sheep, rabbits, poultry, deer and humans have been poisoned after ingesting Poison-Hemlock. It also causes teratogenic (birth defects) effects called crooked calf disease in pigs and cattle. Animal species vary in their susceptibility to acute toxicity. In most cases where ingestion has occurred, especially after the plant has been killed, the end result will be death in a very short time.
Control
Poison Hemlock can be cut, dug up or sprayed with a herbicide containing glyphosate.
Normally, these plants are avoided by grazing livestock but, after cutting or spraying, become
palatable and retain the toxin within the dead plant tissue. Particular care should be taken to keep
livestock away from treated river banks until the controlled plants have decomposed or been
disposed of safely. Particular care should be taken that any poisonous plants are not dumped in
reach of livestock.
DO NOT ALLOW ACCESS FOR LIVESTOCK UNTIL ALL THE PLANT MATERIAL HAS BEEN REMOVED
In situations where these plants are present there will be a risk to animals each time weed control
operations take place. In these circumstances, it may be worth using a herbicide containing
glyphosate to eradicate the plants so as to reduce the risks for future operations.
When a herbicide is used, it is important to fence the area to exclude livestock until all the weed
has died back completely. If the weeds cannot be controlled by herbicide then, for each control
operation, cut weed must be either transported to a safe disposal site or fenced off until all weed
has decomposed or been destroyed by burning.
Care should be taken when cutting or digging up the plant as all parts are poisonous. Wear nonporous
rubber gloves and a face shield for protection from cut ends of stems and contact with
flowers and seeds. The poisonous roots should also be disposed of if the plant is dug up.
Aquatic solutions can porvide qualified operators to apply an approved herbicide to this poisonous plant.