Giant hogweed (Heracleum mantegazzianum) is a tall (up to 15-20 ft), herbaceous, biennial plant.
Origin/Introduction into U.S.:
Giant hogweed is native to central and southwest Asia. It was intentionally introduced via the nursery industry where it eventually escaped and spread.
Giant hogweed suppresses the growth of native plants, which has a negative impact on native wildlife. In addition, giant hogweed poses a threat to human health as direct skin contact with the plant’s toxic sap induces extreme photosensitivity causing slow to heal burns and scarring. this sap can also cause blindness upon contact with the eyes. Costs are incurred for both medical treatment and efforts to keep the plant under control. Over 100,000 seeds per plant are dispersed annually by water, wind, or humans. Giant hogweed is a designated Federal Noxious Weed.
Habitat: Giant hogweed invades disturbed areas across both the Northeast and Pacific Northwestern United States. Although often found in open fields and along roadsides, it has been observed along streams in natural areas.
Leaves: palmately compound, with three deeply incised leaflets, with spotted leaf stalk, enormous, lower leaves can be 5’ wide. Only basal leaves are produced the first year.
Flowers: 50-150 white, small, many borne in large, loose umbels at tops of stems. Blooms late June through August.
Stems: often purple-mottled, up to 4-in in diameter, hollow and ridged.
Fruit/Seeds: flat, oval dry fruit, .375” long, broadly rounded base and broad marginal ridges
Reproduction: by seed
NOTE: Make sure all skin is covered when working with this plant!
Physical/Mechanical Control: Hogweed is difficult to control due to its toxic effects on the skin. A small number of plants can be hand dug, but care should be taken to remove most of the root and to protect skin and eyes.
Repeated mowing does not kill the plant and causes resprouting, but it may weaken the plant if done consistently and persistently enough to starve the roots.
Chemical Control:Foliar treatments with glyphosate or triclopyr have been effective. Glyphosate is considered the most effective herbicide and should be used in spring and early summer when plants are less than three feet tall. A follow-up application in midsummer may be necessary. Use caution around desirable species since glyphosate is non-selective.
For More Information:
Profile photo: New York Invasive Species Information, http://www.nyis.info/index.php?action=invasive_detail&id=45. Giant hogweed burn: USDA APHIS PPQ, Oxford, NC, bugwood.org. Leaves photo: Donna R. Ellis, University of CT, bugwood.org.Flower photo: Terry English, USDA APHIS PPQ, bugwood.org. Stem photos: Leslie J.Mehrohff, University of CT, bugwood.org. Fruit/Seed photo: Cesar Calderon, USDA APHIS PPQ, bugwood.org.