Eric Coombs, Oregon Department of Agriculture, Bugwood.org

Family: Apiaceae (Carrot Family)

Synonym(s):

Duration: Biennial

Habit: Herb

Listed by:
Invasive Plant Atlas of the US: 1
Federal Noxious Weed: 0
TDA Noxious Weed: 0
TPWD Prohibited Exotic Species: 0

Description: Erect, biennial, up to 8' tall forb; stems green with purple spots, freely branched, and hollow; all parts deadly poisonous.
Flower gives an 'umbrella appearance' with white, 5-parted; inflorescence of many 2"-3 1/2" mostly terminal umbels often with 2-4 together from the top stem node. Over time, the side umbels overtop the central one. Blooms are from June to August.

History: Poison hemlock is native to Europe and was introduced into North America in the 1800s as an ornamental.

Biology & Spread: Poison hemlock is an herbaceous (soft stem) plant that reproduces solely by seeds. The seeds separate from the plant when it becomes mature, and despite the plant’s prolific seed production, does not have a mechanism for long-distance seed dispersal. The seeds drop close to the parent plant and may be spread over distance by water, birds, and rodents and remain viable for only two to three years.

Ecological Threat: All plant parts are poisonous; however, the seeds contain the highest concentration of poison. (It was probably used to poison Socrates.) It contains highly poisonous alkaloids toxic to all classes of livestock and humans. Human deaths have occurred from harvesting and consuming the roots as wild carrots or parsnips. It may act as a pioneer species quickly colonizing disturbed sites and displacing natives during early successional areas.

US Habitat: Waste places, weedy areas, and woodland borders.

Distribution

US Nativity: Introduced to U.S.

Native Origin: Europe

US States: AL, AR, AZ, CA, CO, CT, DE, GA, IA, ID, IL, IN, KS, KY, LA, MA, MD, ME, MI, MN, MO, MT, NC, ND, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY

Resembles/Alternatives: There are many species that can resemble Poison Hemlock because of the 'white umbrella of flowers'.
This PDF here can show the difference between this invasive and native such as Ragweed, Elderberry, Yarrow and Angelica.

• It also shows similarities between Poison Hemlock and Giant Hogweed, Wild Carrot and Wild Parsnip.

Management: Due to the noxious nature of the plant, it is highly recommended that you call a professional to handle this plant. You may need to combine mechanical and chemical control for best results, and it may take more than one or two years to control this weed.

Mechanical: If you choose to manage poison hemlock yourself, be sure to wear gloves and other protective clothing including eye wear. Shower afterwards to be sure you have no toxic sap on your skin, and launder your clothes.

Mechanical: There are several herbicides (e.g. glyphosate, or 2,4-D) on the market to control poison hemlock. Most of these herbicides require you to apply it to this weed early in the season when this plant is in a seeding or small rosette stage. This may require you to carefully spot spray the rosette. If it is too late for your chemical control measures for this year, start planning your control measures for next year/next season today!

USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.

Listing Source

Texas Department ofAgriculture Noxious Plant List
Texas Parks and Wildlife Department Prohibited Exotic Species
Invaders Program
Federal Noxious Weed
Union of Concerned Scientists
United States Forest Service Southern Research Station

Text References

(Bailey, L.H. and E.Z. Bailey. 1977. Hortus Third: A Concise Dictionary of Plants Cultivated in the United States and Canada, MacMillan Publishing Co., Inc., New York.

USDA, NRCS. 2001. The PLANTS Database, Version 3.1, National Plant Data Center, Baton Rouge, LA 70874-4490 USA. - http://plants.usda.gov/

USDA Forest Service, Forest Health Staff, Newtown Square, PA. Invasive Plants website: http://www.na.fs.fed.us/fhp/invasive_plants.

Data Source

https://extension.umn.edu/identify-invasive-species/poison-hemlock

https://extension.umd.edu/resource/poison-hemlock-identification-and-management/

Last Updated: 2024-02-08 by Ashley Morgan-Olvera, TISI