Giant Hogweed

Domestic Programs Pest Evaluation. Arthur E. Miller, USDA-APHIS-PPQ, AERO, Raleigh, NC. November 16, 2001

Scientific name: Heracleum mantegazzianum Sommier & Levier (Apiaceae)

Physical description: A biennial or perennial herb growing to 15 feet tall. It has a taproot or fibrous roots. Hollow stems are 2 to 4 inches in diameter with dark reddish-purple spots and bristles. The deeply incised compound leaves grow up to 5 feet in width. GHW has a large umbrella-shaped head up to 2 1/2 feet in diameter across its flat top with numerous small flowers produced in mid-May through July. The plant produces flattened, 3/8 inch long oval dry fruits that have a broadly rounded base and broad marginal ridges.

Origin and North American Distribution: GHW is a native of the Caucasus which has been introduced to Europe, Great Britain, Canada, and the United States as an ornamental. It has become established in New York, Pennsylvania, and Washington state.

Quarantines: GHW is a Federal Noxious Weed and is listed as a Class A weed on the Washington State Noxious Weed List.

Dispersal: Seeds may be distributed and planted as an ornamental, or dried fruits of the plant may be imported as a spice or foodstuff called "golpar" in Iranian cooking. Birds may consume the fruits or mericarps and spread the seeds.

Control: Property managers and cooperators may use these strategies:

Cultural Control. Mowing does not appear to be effective. The Pennsylvania Department of Agriculture has used a rototiller and planted a lawn seed mix to return areas to a natural state.

Chemical Control. The Pennsylvania Department of Agriculture recommends utilizing both pre and post emergent herbicides, plus competitive vegetation. PDA applies Pre-M at 1-1.5 oz./1000 s.f. in late-March. When germination of hogweed seed was noticed, Transline was incorporated at .5 oz./1000 s.f. along with Pre-M at the 1.5 oz/1000 s.f. rate. This continued until other vegetation started to grow. Later in the season, they used Drive at 1 oz./A. Post-emergent applications of 91% Thinvert, 7% Garlon 3A and 2% Transline are initiated in mid-April. These herbicide applications continue until snowfall covers the hogweed.

Previously, glyphosate has been considered the most effective herbicide, but it should be used with caution around desirable plants. The herbicides 2,4-D, TBA, MCPA, and dicamba are not effective on GHW roots. Rodeo (glyphosate) has been recommended in wet areas. Herbicides should be applied to large plants with protective clothing.

Biological Control. In Switzerland 12 phytophagous insect species found on native hogweed have been identified as possible candidates as biological control. Cattle and pigs are cited as possible biocontrol agents.

Economic impact: Giant Hogweed sap causes a skin reaction known as photo-dermatitis or photo-sensitivity, causing large painful blisters with eruptions on humans. In the 1970's, many cases of poisoning were seen in Great Britain where children played with the hollow stems of the plant as pea-shooters or telescopes. In 1998, cyclists complained that contact with "large green plants" left their legs covered in broken and bleeding skin. Contact with the eyes can lead to temporary or permanent blindness.

Environmental impact: It has naturalized in many of the places where it was first introduced. The plants thrive in many habitats but do particularly well where the soil has been disturbed, such as on wasteland, on riverbanks, and along railroads. It prefers moist soil and can quickly dominate ravines and stream banks.

Benefits of control: Giant Hogweed is both a public health and environmental hazard.