Giant Hogweed

TreatmentHeracleum mantegazzianum


Giant hogweed is designated as a Federal Noxious Weed, because it produces sap that causes skin sensitivity to UV radiation and leads to blistering and severe burns. Learn more about this invasive plant in Vermont


Giant hogweed is a herbaceous biennial that can grow up to 7-20 feet tall. Hollow stems are 2-4 inches in diameter with dark reddish-purple spots and bristles.


The leaves are deeply lobed, sharply pointed. They can be up to 9.8 feet in breadth.


Flowering occurs in late spring to early summer. The white flowers are on a large umbrella-shaped head at that can be up to 2.5 feet in diameter, with 50+ rays per cluster.


Flattened, 3/8 inch long oval dry fruits that have a broadly rounded base and broad marginal ridges.


View New York State's excellent identification summary, including comparisons to native plants including cow parsnip.

a chart comparing hogweed to other plants found in Vermont that look similar



Ecological Threat

Because of its size and rapid growth, giant hogweed is an aggressive competitor capable of displacing native plants. It dies back during the winter months, leaving bare ground open to erosion on riverbanks and steep slopes. The sap of giant hogweed makes human skin sensitive to ultraviolet light, resulting in severe burns and blisters. Contact with the eyes can cause permanent blindness.


Giant hogweed is native to Europe and Asia. It was first introduced into the United States in 1917 for ornamental purposes.


Giant hogweed can invade a variety of habitats but prefers moist, disturbed soils such as riverbanks, ditches and railroad right-of-ways.

Life Cycle

Giant hogweed sprouts in early spring and flowers early July. This perennial plant dies back after flowering, leaving tall dead stalks. It forms perenating buds which lie dormant through winter until the next growing season. It reproduces by seed dispersal only, not vegetatively. Each flower head contains approximately 1500 seeds, which can remain viable for up to ten years. 

Management Options

***Check out the downloadable treatment sheet above***

Mechanical Management

CAUTION: The sap from this plant is dangerous. If it gets on your skin and you are exposed to the sun, it can cause severe burns.

Always wear thick gloves and long pants and shirts.

Manual treatment can be moderately to highly effective for giant hogweed

Giant hogweed leafs out very early compared to most native vegetation, thus making it easy to detect. It is beneficial to manually remove this plant before it begins flowering later in the growing season

Hand Pulling/Digging

  • Pull entire plant by the base of the stem or dig roots with a shovel
  • Be sure to remove entire root system
  • Dry all vegetation (most importantly roots) or collect vegetation and dispose of in a landfill


  • Cut at least 1 time before seeds appear (until July)
  • Repeat for 3-5 years

Chemical Management

Active ingredients commonly used in herbicides: Glyphosate or triclopyr.

  • Be careful not to damage or kill nearby native plants when conducting management work.
  • Always read and follow pesticide label directions. Application of pesticides may require a certification from the Agency of Agriculture, Food and Markets. The Agency website provides information on what applicator certification is needed.

If foliar spraying only:

  • Foliar spray later in the summer (June-mid July)
  • Spray leaf surfaces with low volume backpack sprayer, or high volume mist blower

Low Volume Backpack Sprayer

  • Herbicides (active ingredient): glyphosate or triclopyr with surfactant
  • Used to giant hogweed plants and minimize drift to desirable species



Photo Credit

Terry English, USDA APHIS PPQ,

Donna R. Ellis, University of Connecticut,

Rob Routledge, Sault College,

Robert Videki, Doronicum KFT,

USDA Aphis PPQ Oxford NC,

Information Credit, Giant hogweed

Video: Invasive Species Council of Greater Vancouver, Giant Hogweed

PA Dept Conservation and Natural Resources, Giant Hogweed 

GoBotany, Giant Cow-parsnip 

Vermont Chapter of The Nature Conservancy