| giant hogweed |
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giant hogweed (heracleum mantegazzianum)
ODA rating: A and T
Description
Perennial; flowers May-July. Grows 10-15 feet tall. Stalk and flower head develop after two to four years, then the plant dies back. Stalks are two to four inches in diameter, hollow, have reddish-purple blotches and pustules with a single erect hair in the center. Flower head is a large umbrella-like inflorescence up to two and one half feet in diameter. Leaves are three to five feet wide, compound and deeply incised. This plant closely resembles native cow parsnip which rarely exceeds six feet with a flower head 8-12 inches wide. Cow parsnip is a common native plant in the northwest and grows in riparian areas and roadsides. Giant hogweed is a member of the carrot or parsley family and its most impressive characteristic is its massive size.
Impacts
This plant is a health hazard to humans. Because of its invasive nature it soon becomes a pest within the garden and readily escapes. It has naturalized in many of the places where it was introduced, and is one of the most invasive weeds in Europe.
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 Images courtesy of Tim Butler, Oregon Dept. of Agriculture |
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If images are downloaded and used from the ODA web site please be sure to credit the photographer.
Known hazards
This plant is a public health hazard. Do not expose bare human skin to the plant or breathe the smoke from fires if it is being burned. The plant exudes a clear watery sap which sensitizes the skin to ultraviolet radiation. Humans often develop severe burns to the affected areas resulting in blistering and painful dermatitis. Blisters can later develop into purplish or blackened scars.
Introduction
Giant hogweed grows as a native in the Caucasus Mountains, a region of Asia between the Black and Caspian seas. Planted as a curiosity in arboretums and private gardens in Europe and North America early in the twentieth century, it soon escaped and naturalized in surrounding areas, especially riparian and urban sites. It is reported to be a problem weed in Europe, England, Scotland, Scandinavia and Germany. In North America it grows in Ontario, British Columbia, Maine, Maryland, New York, Washington and now in Oregon.
Distribution in Oregon
Map legend
Yellow: limited distribution
Red: abundant
Grey: not known to be present
Biological controls
Biological control agents are not used on "A" listed weeds in Oregon. This weed is being managed for eradication or containment.
Informational links
WeedMapper
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