Invasive Species: Poison Hemlock

Conium maculatum

Poison Hemlock is a native of Europe, Asia, and North Africa.

It was first documented in 1919 in Multnomah County.

Why is it important to control?

Poison hemlock thrives along streams, in agricultural ditches and in pastures. This species is highly toxic to livestock and humans. It spreads only by seed which can be dispersed by wind, water, animal fur, human clothing and boots, and machinery.

How can you identify it?

Poison Hemlock (Conium maculatum) stem closeupPoison Hemlock (Conium maculatum) flower close up
Habitat: Pastures, along waterways and ditches
Life Cycle: Biennial
Height: 3-7ft
Leaf Description: Leaves are alternate, one per node, petioled(having a stem), and pinnately divided
Fruit & Flower Description: Flowers are white compound umbels like umbrellas
Bloom Time: May-June

How do you control it?

  • Digging can be effective when caught early and plant population is small. Wear rubber gloves and mask.

  • Do not burn the plant, as the smoke can contain deadly toxins.

  • Herbicide control:  Oregon State University Extension recommends a glyphosate or triclopyr based herbicide. Take care to avoid drift and be cautious near crops. FOLLOW ALL LABEL DIRECTIONS!

  • There is a small Agonopterix moth that frequently defoliates hemlock patches, unfortunately its impact is sporadic from year to year.

How to report it?

There are various ways you can report this noxious weed.

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