Giant hogweed (Heracleum mantegazzianum)

Giant hogweed can grow up to 15 feet tall and produce large clusters of white flowers. If a person gets the sap on their skin and their skin is exposed to sunlight it can cause chemical burns. It is not known to be present in Minnesota and is a prohibited noxious weed on the eradicate list. Cow parsnip (Heracleum maximum) is a common native plant in Minnesota that looks very similar to giant hogweed. Due to the health hazard of giant hogweed and how similar it looks to a common native plant, suspected plants should be reported to the Minnesota Department of Agriculture to confirm identification and consult on next steps.

Description

Appearance

Giant hogweed can grow up to 15 feet tall, produce large clusters of white flowers that can be 2.5 feet wide, and have leaves up to 5 feet wide. It looks very similar to the native plant cow parsnip.

Leaves and stem

In mature plants, individual leaves can be up to 5 feet wide and as tall as a person. Leaves attach to the stem alternately (one leaf per node). Leaves are deeply lobed with serrated leaf edges. Giant hogweed produces a cluster of leaves close to the ground (a rosette) from its base in its first year and does not flower. The rosette stage can last up to five years before the plant flowers. The leaves in the rosette are often not deeply lobed. When the plant flowers, it sends up a tall flower stalk with deeply incised leaves. The underside of the leaves have white hairs.

The stem can reach 2-4 inches in diameter. Stems are hollow and have white hairs and purple splotches.

Flowers

The flowering heads are made of many small white flowers in multiple clusters. The flowering heads can be up to 2.5 feet wide. The individual flowers have 5 petals. Flowers bloom from May to July.

Seeds

When seeds mature they are brown, flat, and oval. Seeds have four brown lines (oil tubes) on them.

Roots

Giant hogweed has a deep taproot.

Biology

Giant hogweed produces a cluster of leaves close to the ground (a rosette) in its first year and does not flower. It may take up to five years for the plant to send up the tall flower stalk. The plant dies after flowering. Plants can grow in full sun to partial shade. Plants can grow in moist areas, ditches, roadsides, pastures, stream banks, and other open areas.

Origin and spread

Giant hogweed in native to Asia. It was introduced the United States as an ornamental plant. It has spread from areas where it was planted. It has not been found in Minnesota, but is known to be in Wisconsin.

Refer to EDDMapS Distribution Maps for current distribution.

Don't be fooled by these look-alikes

• Cow parsnip, Heracleum maximum, formerly Heracleum lanatum (native) – Cow parsnip has leaves that are less deeply incised than giant hogweed. Cow parsnip is generally 5-9 feet tall when mature so is shorter than mature giant hogweed. Cow parsnip is a common native plant in Minnesota and is often mistaken for giant hogweed.
• Angelica, Angelica atropurpurea (native) – Angelica flower clusters are more ball-shaped than giant hogweed. Angelica leaves have 5-11 leaflets. Angelica is a common native plant in Minnesota and can be mistaken for giant hogweed.
• Poison hemlock, Conium maculatum (invasive) – Poison hemlock leaves have a delicate, lacy, fern-like appearance.
• Wild parsnip, Pastinaca sativa (invasive) – Wild parsnip has yellow flowers and is generally about 4 feet tall.
• See additional identification guides listed in the "Resources" section of this webpage for side by side comparisons, such as the giant hogweed identification and look-alikes guide from the New York Department of Environmental Conservation.

 

Regulatory classification

This species is a Minnesota Department of Agriculture Prohibited Noxious Weed on the Eradicate List meaning that the above and belowground parts of the plant must be destroyed. Additionally no transportation, propagation, or sale is allowed.

Threat to Minnesota

• Giant hogweed has the potential to impact human health. Giant hogweed sap has a chemical that can cause chemical burns when the sap is on skin and then skin is exposed to sunlight. Temporary and permanent blindness have been reported from sap in the eyes.
• It produces abundant seed and can form dense cover reducing habitat for native plants.

What you should do

One way that invasive plant seeds and fragments can spread is in soil.  Sometimes plants are planted purposefully.  You can prevent the spread of invasive plants.

PlayCleanGo: Stop Invasive Species in Your Tracks

• REMOVE plants, animals and mud from boots, gear, pets and vehicle.
• CLEAN your gear before entering and leaving the recreation site.
• STAY on designated roads and trails.
• PLANT non-invasive species.

Native substitutes

• Cow parsnip (Heracleum maximum, formerly Heracleum lanatum)
• Tall meadow rue (Thalictrum dasycarpum)
• Culver's root (Veronicastrum virginicum)
• Flowering spurge (Euphorbia corollata)
• Virginia mountain mint (Pycnanthemum virginianum)

 

Control methods

Due to the need for extensive personal protective equipment while managing giant hogweed, contact the Minnesota Department of Agriculture for advice on managing this plant.

Reporting

Report new occurrences by submitting a report through EDDMapS, emailing Report a Pest, calling Report a Pest (1-888-545-6684), or contacting your local county agricultural inspector

Resources

• Identification
  • Giant hogweed identification and look-alikes (New York Department of Environmental Conservation)
  • Mistaken Identity - Invasive Plants and their Native Look-Alikes (Delaware Department of Agriculture)
  • Giant hogweed identification training module (Midwest Invasive Species Identification Network)
  • Video on distinguishing giant hogweed from native cow parsnip (Greater Vancouver Invasive Plant Council)
• Identification and management
  • Identification and management of giant hogweed (Minnesota Department of Agriculture)
  • Identification and management of Minnesota Noxious Weeds (MN Department of Transportation)
  • Identification and management of giant hogweed (Michigan State University)