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Giant Hogweed

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(Heracleum mantegazzianum)

Giant Hogweed is an invasive weed species that can cause skin irritation, blistering and burning upon contact. The plant has moved into Ontario and British Columbia at this time and recent media stories have raised local public concerns and interest in the plant.

According to Alberta Agriculture and Rural Development, the plants reported in Alberta to date have proven to be Cow Parsnip. Strathcona County has developed a comprehensive excerpt about determining the difference between Giant Hogweed and Cow Parsnip.

Giant hogweed (Heracleum mantegazzianum) has numerous small white flowers clusters in an umbrella-shaped head, with stout, hollow green stems covered in purple spots. Dark green leaves are coarsely toothed in 3 large segments with stiff underside hairs, and lower leaves can exceed 2.5 metres in length. Giant hogweed can grow up to 5 metres in height at maturity.

Giant hogweed is a highly competitive plant due to vigorous early-season growth, tolerance of full shade and seasonal flooding, as well as its ability to co-exist with other aggressive invasive plant species. Each plant can produce up to 100,000 winged seeds (typically 50,000) that remain viable in the soil for up to 15 years. Plants generally die after flowering.

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.