Giant Hogweed

TreatmentHeracleum mantegazzianum

Invader Images

    • Giant hogweed has thick, hollow stems, with purple patches and course bristles
      Giant hogweed has thick, hollow stems, with purple patches and course bristles
    • Giant hogweed flower clusters have an "umbrella shape"
      Giant hogweed flower clusters have an "umbrella shape"
    • Giant hogweed can reach heights of 15-20 feet
      Giant hogweed can reach heights of 15-20 feet

Common Look-alikes

    • American cow parsnip (native to North America) is large, but has flat-topped flower clusters
      American cow parsnip (native to North America) is large, but has flat-topped flower clusters

Identification

Giant hogweed is a tall (up to 15-20 ft. [4.6-6.1 m]), herbaceous, biennial plant that invades disturbed areas across both the Northeast and Pacific Northwestern United States. 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. The large stem is hollow and usually marked with purple blotches. The leaves are deeply lobed, sharply pointed, and up to 5 ft. (1.5 m) wide. 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 ft. (0.8 m) in diameter. Giant hogweed can invade a variety of habitats but prefers moist, disturbed soils such as riverbanks, ditches and railroad right-of-ways.

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

 

Biology

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.

Origin

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

Habitat

Forests, forest edges, meadows, fields, disturbed areas

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

Mowing/cutting

  • 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

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

**Be careful not to damage or kill nearby native plants when conducting management work. And when using herbicides, always follow the instructions on the label.**

Citations

Photo Credit

Giant Hogweed next to building, UGA1151035, Terry English, USDA APHIS PPQ, CC 3.0

Giant Hogweed flower clusters, 1460061, Donna R. Ellis, University of Connecticut, CC 3.0

Giant Hogweed, 5474254, Rob Routledge, Sault College, CC 3.0

American Cow Parsnip, 5382426, William M. Ciesla, Forest Health Management International, CC Non-com 3.0

Information Credit

Invasive.org, 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