Giant Hogweed

Plant Protection and Quarantine

August 2002

The U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) regulates giant hogweed (Heracleum mantegazzianum) as a noxious weed. This weed, which can be either biennial or perennial, grows to a height between 8 and 15 feet. Giant hogweed often has a taproot but can also have fibrous roots. It has hollow stems between 2 and 4 inches in diameter with dark reddish-purple splotches and pustulate coarse white hairs or bristles. The deeply incised compound leaves grow up to 5 feet in width. Hairs on the underside of the leaf are stiff, dense, and stubby. The large umbrella-shaped flower heads are up to 2 1/2 feet in diameter across a flat top with numerous small flowers. The small flower appears from mid-May through July. Giant hogweed produces flattened, oval-shaped fruit with a broad, rounded base and wide marginal ridges. This weed sprouts in the early spring from the roots or seed.

Giant hogweed, which is native to the Caucasus, has been introduced into Europe, Great Britain, Canada, and the United States. Although it is listed as a Federal noxious weed and is illegal to bring into the United States or move across State lines, giant hogweed is known to occur in New York, Pennsylvania, and Washington. Reports of infestations have been received from Maine, Michigan, and Washington, DC. This weed has been planted as an ornamental in the United States and may have also been brought into this country for its fruit, used as a spice (golmar) in Iranian cooking.

Giant hogweed is likely to naturalize in many of the places where it has been first introduced. The plants thrive in many habitats but do particularly well where the soil has been disturbed, such as on wastelands, riverbanks, and along railroads. The weed prefers moist soil and partial shade, and can quickly dominate an area where the conditions are just right.

Both people and animals may have a sensitivity toward the giant hogweed's sap. Furocoumarins in the sap can cause a skin reaction known as photodermatitis. When photodermatitis occurs in people, their skin becomes sensitive to ultraviolet light in sunlight. This sensitivity can lead to long-lasting swelling and blisters. Contact with the eyes can cause temporary and sometimes permanent blindness.

Figure: Heracleum mantegazzianum. A. Portion of leaf, showing its large and compound nature; B. Portion of inflorescence (a compound umbel); C. Portion of umbel in flower (A-C all 0.65x); D. Individual staminate flower from lateral inflorescence, top view; E. Fruit (a schizocarp), side and edge views; F. Mericarp, following dehiscence of schizocarp (D-F all 2.5x).

Sources: A. French 2122, Oregon (NY); B-F. Dixen et al.
488, Denmark (MO)

APHIS' Federal noxious weed program is designed to prevent the introduction into the United States of nonindigenous invasive plants and to prevent the spread of newly introduced invasive plants within the United States. Noxious weed activities include exclusion, permitting, eradication of incipient infestations, survey, data management, public education, and (in cooperation with other agencies) integrated management of introduced weeds, including biological control.

For more information on giant hogweed, contact Dr. Alan Tasker, the Federal Noxious Weeds program coordinator, at (301) 734-5708 or e-mail him at Alan.V.Tasker@aphis.usda.gov

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

Click here for printable file (PDF)