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Poison Hemlock

Adult poison hemlock plant. Photo credit: Joseph M. DiTomaso, University of California - Davis, Bugwood.org

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Common Name: Poison Hemlock
Scientific Name: Conium maculatum
Origin: Europe

Description

Poison hemlock is biennial herbaceous plant that forms a rosette in the first year and grows a tall flower stalk in the second. Its fern-like leaves are at least 2 feet long and pinnately compound. White flowers, in umbels 3-6 inches long, bloom from May to August. The stem is hairless, hollow and mottled with purple (In comparison, giant hogweed stems have coarse hairs).

Habitat

Poison hemlock thrives in disturbed areas such as roadsides, ditches, stream banks, and pastures. It can also be found in wetlands and riparian forests.

Threat

Poison hemlock produces massive amounts of seed and crowds out native vegetation. It also emerges in early spring, making it more appealing to wildlife and livestock. Ingestion of poison hemlock can be fatal for livestock and humans.
Symptoms of poisoning include nervousness, trembling, ataxia, dilation of the pupils, a weak and slow heartbeat, and coma. Symptoms generally begin within an hour of ingestion.

Management

CAUTION: Poison hemlock is extremely toxic to humans. When working with poison hemlock, wear Personal Protective Equipment (PPE) to limit accidental ingestion.
Plant removal can be achieved through mowing, hand removal, or herbicide application. Management should take place before flowering to limit seed production and spread. Treatments need to be repeated for several years until the seed bank is depleted. Establishing vegetation, such as native grasses, in the treatment area reduces likelihood of re-infestation. Since poison hemlock is so easily spread by seed and mowing, care must be taken to use spread prevention practices when mowing.

Regional Distribution

Common

WNY PRISM Priority

Tier 4 – Local Control

NYS Invasive Species Tiers Chart – Tier Definitions

Pathways

Poison hemlock was introduced to North America as an ornamental plant. It produces numerous seeds which can be spread through mowing and  transport on footwear, clothing, and equipment.

Native Alternatives

Great angelica (Angelica atropurpurea)

Warm season grasses