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Giant Hogweed Identification

Updated on September 13, 2012
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Sean has been in the industry of gardening and landscaping since 2006. He is also a certified arborist that tends to focus on plant health.

Common Name
Giant Hogweed

Latin Name
Heracleaum mantegazzianum

Flowering Hogweed

Identifying Giant Hogweed

Giant hogweed is labelled as a noxious and dangerous weed. It is a tall, robust, herbaceous biennial or monocarpic perennial. Giant hogweed can grow up to 16 feet tall with large hollow stems. It stays in a basal rosette stage for several years before growing many feet in height. The basal rosette stage has no prominent stem and resides close to the ground.

The sap of mature giant hogweed causes phytophotodermatitis. Contact with skin in the presence of sunlight causes severe rashes, blisters, and skin discoloration. Wear gloves, long sleeves, and long pants when handling giant hogweed. If sap is contacted, one must go indoors and gently wash the sap off. Burns may even occur after washing, depending how long the skin was exposed.

Giant hogweed invades woodland areas, roadsides, and disturbed soils. It prefers areas with moist soils and some shade, such as stream banks.

Giant hogweed leaves are compound and about 1 to 5 feet wide. They are deeply palmate with pointed lobes. The undersides are covered in coarse white hairs.

The flowers are white, 5-petaled flowers in large flat-topped umbels. They bloom from May to July. The flowers can be up to 2.5 feet wide.

The dry fruits are two-winged and contain one flattened, oval seed in each fruit.

One large, deep taproot.

Ecological Threats of Giant Hogweed

Giant hogweed can easily overcrowd native vegetation, increase soil erosion, and can easily disperse seed into waterways. The taproot is deep and difficult for nature to eliminate.

Hogweed Burns

Burns suffered from Giant Hogweed sap and sunlight exposure
Burns suffered from Giant Hogweed sap and sunlight exposure | Source

Eradication of Giant Hogweed

Mechanical Eradication
A shovel can be used to sever the taproot from the stem. Dig into the root a few inches below the soil surface before seeds develop. Promptly burn, bag or landfill the flower heads.

Chemical Eradication
Foliar spray herbicides with glyphosate are effective. Spray should also be applied to a freshly cut stump. Apply herbicides according to their label directions, and always use personal protective equipment. Be very careful to eliminate pesticide drift that may contact non-target plants. Always use the correct personal protective equipment.


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      ctbrown7 6 years ago

      Thanks for the reminder to avoid hogweed. Those burns look terrible.


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