Giant Hogweed

TreatmentHeracleum mantegazzianum

Images of this species:

Common look-alikes:

Identification

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.

Appearance

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.

Foliage

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

Flowers

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.

Fruit

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

Look-a-likes

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

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

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

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.

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.