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Most of the time, weeds simply bother gardeners by crowding out more desirable plants in lawns and shrub beds. We often consider weeds annoying but seldom dangerous. However, several in the Northwest have chemical components that can harm animals or humans if eaten. Most of these are on the Washington State Noxious Weed list.
Tansy ragwort (Tanacetum vulgare) for instance, produces alkaloids
that can kill cattle and horses, and it must be controlled in fields and pastures.
Most dangerous to people are the hemlocks, including poison hemlock, Conium
maculatum. This toxic plant was introduced to North America from Europe, and
has often been mistaken for a garden ornamental. The plant is attractive, but
can be dangerous or even lethal to people and animals.
Poison hemlock is a member of the wild carrot family, and is common throughout western Washington, along waterways, and in cultivated areas. In mid-summer its white flowers show along roadsides and in open fields. It resembles anise or wild parsley, and is classified in the family Umbelliferae, the parsley family. All parts of this plant are poisonous to humans: leaves, stems, roots,and seeds (particularly the seeds.). Poison hemlock contains volatile alkaloids that have been used as a poison since ancient times. The famous incident of Socrates' death in Athens in 329 BC occurred when he was reportedly given the juice of this poison hemlock plant to drink. Children have been sickened by pulling the hollow stems and using them as straws.
How can you identify it? Look closely at the stem of any plant you may suspect of being poison hemlock. The stem is hollow, smooth (not hairy) and marked with purple streaks and blotches. These blotches and streaks on a green hollow hairless stem, and the mottled purple spots, are identifiers of the plant. The purple mottling makes the stems appear menacing in a fairy-tale sort of way. The finely divided leaves are fern-like. . An excellent color photo of this is posted on the King County Noxious Weed Board web site. Photos of tansy ragwort, mentioned above as potentially fatal to livestock, are also pictured. A water-dwelling relative of poison hemlock, called western water hemlock, Cicuta douglasii, grows in very wet meadows and long streams, having flowers resembling the poison hemlock and hollow roots that are strongly poisonous. Strangely, waterfowl such as ducks eat the seeds of this plant, but it cannot be tolerated by livestock or humans.
Poison hemlock is a biennial; it grows from seeds, and produces, during the first year, a rosette of fern-like leaves close to the ground. The second season it bolts to form the tall, erect, flowering stems which can be from 4 to 8 feet tall. The white flowers develop into green, ridged seed capsules which turn brown when the seeds mature.
Poison hemlock must be removed. Dig it out, and do not allow this weed to go to seed. Wear gloves when handling it. Don't put it into the compost -dead stalks can remain poisonous for two or three seasons. Don't incinerate it.
If you need more help identifying this or other troublesome weeds, contact
your local Noxious Weed Control Board. They will help with photos and information
about getting rid of the weed. In King County call 253-872-2972. In Pierce County,
call 253-798-7263.
Hortsense: Managing plant problems with Integrated Pest Management
