Giant Hogweed

Giant hogweed (Heracleum mantegazzianum) is a tall (up to 15-20 ft), herbaceous, biennial plant.

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.
hogweed skin


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.    hogweed leaves

Flowers: 50-150 white, small, many borne in large, loose umbels at tops of stems. Blooms late June through August.

hogweed flower

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

hogweed stem

hogweed stem open

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

hogweed seeds

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 roots 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.

NYS Department of Environmental Conservation Giant Hogweed Control Program

From late April through August, NYS DEC field crews visit each confirmed giant hogweed site and use the appropriate control method. This is free of charge to the landowner. In general, root-cutting is used at smaller sites with less than 400 plants, the herbicide is used at larger sites with greater than 400 plants and flower/seed head removal is used at all sites to limit seed dispersal. Sites are visited each year until the plants are eradicated. When no more plants are found the site will be monitored for three subsequent years.

For a site to be visited and controlled, landowners must give annual permission. For crews to use herbicide control, landowners must first sign a property permission form. Learn more at the NYSDEC website

Report: ghogweed@dec.ny.gov or call the Giant Hogweed Information Line: 845-256-3111. Provide photos, and detailed directions to the plant infestation (GPS coordinates and street address a plus) and estimate the number of plants.


For More Information:

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.

Photo Credits:

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.


Prevent the introduction of invasive species into the SLELO PRISM.

Rapidly detect new and recent invaders and eliminate all individuals within a specific area.

Share resources, including funding personnel, equipment, information, and expertise.

Collect, utilize, and share information regarding surveys, infestations, control methods, monitoring, and research.

Control invasive species infestations by using best management practices, methods and techniques to include: ERADICATION (which is to eliminate all individuals and the seed bank from an area), CONTAINMENT (which is reducing the spread of established infestations from entering an uninfested area) and SUPPRESSION which is to reduce the density but not necessarily the total infested area.

Develop and implement effective restoration methods for areas that have been degraded by invasive species and where suppression or control has taken place.

Increase public awareness and understanding of invasive species.

Develop and implement innovative technologies that help us to better understand, visualize, alleviate or manage invasive species and their impacts or that serve to strengthen ecosystem function and/or processes.

Rob Williams                              rwilliams@tnc.org                     Program Director

Megan Pistolese megan.pistolese@tnc.org
Outreach and Education

Brittney Rogers brittney.rogers@tnc.org 
Aquatic Invasive Species

Robert Smith       robert.l.smith@tnc.org 
Terrestrial Invasive Species

Zachary Simek    zachary.simek@TNC.ORG     Conservation and GIS Analyst

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