Giant Hogweed

Heracleum mantegazzianum

ERADICATE

Giant hogweed is an aggressive invader that was first introduced to North America as a garden ornamental. It closely resembles our native plant cow parsnip, except the taller giant hogweed can grow up to 6-metres or more; while cow parsnip grows to no more than 2-meters.

* If you find Giant Hogweed, please Report it!

Warning: Giant hogweed stem hairs and leaves contain a clear, highly toxic sap that, when in contact with the skin, can cause burns, blisters and scarring. WorkSafe BC has issued a Toxic Plant Warning for Giant hogweed that requires workers to wear heavy, water-resistant gloves and water-resistant coveralls that completely covers skin while handling the plants. Eye protection is also recommended.

Family: Apiaceae (Carrot).

Other Common Names: Giant Cow-parsnip, Hogweed

Origin: Asia

Description: Herbaceous perennial. Stems are hollow, ridged, green with purple spots to purple – red, may have stiff hairs present. When in flower, plants can grow to 6 meters tall. Flowers have small white flowers clustered in large umbrella-shaped head and up to 1.5meters across. Leaves are green and deeply incised (almost to leaf vein) and have 3 segments. Leaves can exceed 2.5 m in length.

Look-a-likes: Cow Parsnip, Palmate Coltsfoot

Reproduction: Flowers are formed after 1-4 years of growth. Each flower head produces 100,000 seeds; which can persist in the soil for up to 15 years.

Legal Status: Weed Control Act, Community Charters Act, Listed under Bylaw 2347 in the Comox Valley Regional Districts’ Weed Control Regulation Bylaw

Impacts:
Agricultural: Can infest agricultural areas. Ecological: Strongly competitiveplant; dense stands of very, tall plants outcompete native species. Roots are shallow compared to mixed native communities, which may increase erosion risks in riparian areas.
Human: Sap which gets on skin causes hypersensitivity to sunlight; resulting in irritation, blistering and dermatitis which is re-aggravated with exposure to sunlight for several years. Scarring and blindness may result.

Habitat: Adapted to rich, damp soil and tolerates a wide range of light regimes. Grows on wet to moist disturbed sites at low elevations. Inhabits streams, wetlands, ditches, roads, right-of-ways, agricultural areas, wooded ravines, vacant lots, and other disturbed sites.

Distribution: Present in all Regional Districts within the Coastal ISC Service Area. Widespread in Nanaimo area, common in Comox Valley, Cowichan Valley and Strathcona. Limited in Alberni-Clayoquot, Capital, Sunshine Coast and Powell River. Most common in CDFmm and CWHxm but also reported in CWHvm and CWHvh.

Management Strategy: Use protective clothing and eyewear when handling all parts of this plant! Cut off flowers to prevent seed formation. Excavate plants, severing roots 8-12 cm below the soil surface. DO NOT COMPOST; dispose of all plant parts in strong garbage bags. Return to site to check for regrowth. Immature plants can be controlled by covering with black plastic or by mowing at 2 week intervals; 3-5 years of follow-up treatment may be required. Chemical controls can be effective, foliar applications are most effective in spring followed by a summer application on late appearing sprouts. Stem injections or cut stem and injections are effective after heavy sap flow in spring. No biological control agents are available.