Giant Hogweed

Giant hogweed (Heracleum mantegazzianum) is a tall (up to 15-20 ft), herbaceous, biennial plant that invades disturbed areas across both the Northeast and Pacific Northwestern United States.

Although often found in open fields and along roadsides, it has been recently observed along streams in natural areas. Giant hogweed is native to central and southwest Asia.

Impacts

Giant hogweed has two major impacts: ecological and human health. It suppresses growth of native plants, which has a negative impact on the wildlife that depend on them. In addition, direct skin contact with giant hogweed induces extreme photosensitivity, which can lead to severe, slow to heal burns and scarring. It 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.

Identification

Habitat: disturbed soils, roadsides, stream and river banks, railway embankments, and fallow fields.

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.

Giant hogweed flowers resemble those of a very large Queen Anne's lace.

Stems: often purple-mottled, up to 4-in in diameter, hollow and ridged.

Fruit: flat, oval dry fruit, .375” long, broadly rounded base and broad marginal ridges

Reproduction: by seed

Control/Management

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.

An infestation of giant hogweed

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.

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 nonselective.

For more information on control methods, visit the New York State Department of Environmental Conservation Giant Hogweed Control page.

NOTE: Make sure all skin is covered when working with this plant!

Difficult to control due to damage it posses to skin. A small number of plants can be hand dug. Repeated mowing weakens the plants but the large root can remain alive for many years. Foliar treatments with glyphosate or triclopyr have been effective. Make sure all skin is covered when working with this plant.

For More Information:

New York State Department of Environmental Conservation fact page
Giant Hogweed Statewide Distribution Map (2008)
Giant Hogweed (nyis.info)
Giant Hogweed (www.invasive.org)

__________________________________

Select another species