Giant Hogweed, invasive, phototoxic

Giant Hogweed (Heracleum mantegazzianum)

WARNING: DO NOT TOUCH THIS PLANT! Giant Hogweed is a perennial herb that grows up to 5 metres tall (16 feet). It looks very similar to the native cow parsnip (Heracleum maximum). It has large umbrella-shaped flower heads that are small white flower clusters. The stems are hollow with purple spots and the leaves are dark green, resembling a coarsely-toothed maple leaf. It produces up to 50,000 seeds. It spreads by seed and buds from the crown and rootstock.

LRISS Category: PREVENT

Habitat & Ecology

Giant Hogweed was introduced from Asia as an ornamental plant. It flourishes at the coast and in wet places in BC. It prefers rich, wet soils and can tolerate varied amounts of light. Large stands can form in riparian areas and ditchlines.

Impacts

This plant is a health hazard to humans and pets. The leaves and stem contain a poisonous sap that when it comes into contact with human skin and is exposed to sunlight, it causes serious burns and blisters. Blisters can reoccur for up to 10 years later if the area is exposed to the sun again. When working around this plant, full protective gear is necessary (refer to Worksafe BC guidelines). Ecologically, hogweed is very competitive and can out complete native species.

Management

LRISS does not recommend treating this plant at all. Hire a knowledgeable contractor due to the risk of burns. If removing a small infestation (e.g. less than 1 m square), use rubber gloves, protective clothing and eyewear and follow the Worksafe guidelines.

References

BC Government. 1996, 2016 edition. Field Guide to Noxious Weeds and other Selected Invasive Plants of British Columbia. Ninth Edition.

Invasive Plant Council of BC. April 2008. Giant Hogweed Targeted Invasive Plant Solutions.