Giant Hogweed

Description

Giant Hogweedis an invasive perennial and a member of the carrot or parsley family (Apiaceae), originating from Asia and Eastern Europe. Introduced for ornamental purposes, it has since escaped cultivation and spread across various parts of Canada, including Ontario and British Columbia. It poses a significant threat not only to human health, with its toxic sap causing severe dermatitis, but also to local ecosystems by outcompeting native flora [1].

  • Scientific name: Heracleum mantegazzianum

  • Common name(s): Giant Hogweed

  • French name: Berce du Caucase

  • Regulatory status: Giant Hogweed has been recognized as a significant invasive and noxious weed in various provinces across Canada due to its harmful effects on human health and negative impacts on biodiversity and ecosystems. Specific regulatory actions and statuses can vary by province.

Giant Hogweed

© Kasper Malmberg via iNaturalist.org, used under CC BY

Habitat

This species is adaptable to various soil moisture conditions and thrives along moist area edges, in meadows, and is increasingly found in forage and pasture fields near river flats. Although Giant Hogweed prefers sunny locations, it can also grow in partially shaded areas. [2]

Identifying Features

  • Growth Pattern: Can reach a towering height of up to 4.5 meters, with a rapid growth rate of up to 10 cm/day in early spring.

  • Stems: Hollow, up to 10 cm in diameter, covered in reddish-purple speckles and short whisker-like hairs.

  • Leaves: Deeply lobed and toothed, basal rosette leaves can span up to 1 meter wide on large plants. Stem leaves are similar but smaller.

  • Flowers: Features a large, umbrella-shaped flowering head, 40–60 cm wide, composed of small white petals. This species flowers every 3 to 4 years and can be commonly confused with the native species Cow Parsnip.

  • Seeds: Oval, about 10 mm long, yellowish-brown with prominent oil ducts.

    Giant Hogweed Fact Sheet, Capital Regional District (CRD) 2021

Impacts

  • Causes phytophotodermatitis, a skin irritation that can cause blisters and long-term sensitivity to sunlight in humans. In some cases, its sap has even led to blindness.
  • Crowds out native vegetation, reducing plant biodiversity.
  • Can potentially spread into various environments, particularly impacting riverbanks, roadsides, and open fields.

Management and Control

Managing Giant Hogweed requires caution due to its toxic sap. Effective measures include:

  • Wearing protective eyewear and gear to avoid skin contact, however it is recommended to consult a professional to undertake removal and management.
  • Manual removal by digging up small populations, ensuring the entire root is removed.
  • Disposal of plant material securely to prevent seed spread.
  • Chemical control through licensed pesticide applicators.

What You Can Do

  • Learn to identify Giant Hogweed and distinguish it from similar species like cow parsnip.
  • Avoid touching or handling the plant without proper protection.
  • Report sightings to local environmental agencies or through invasive species reporting tools like iNaturalist.ca.
  • Support and engage in local eradication efforts where possible.
  • PlantWise – plant only native and non-invasive plants in your garden. www.Plant-Wise.ca

For more detailed information on identifying and safely managing Giant Hogweed and to support conservation efforts, please visit resources such as:

  • https://www.ontarioinvasiveplants.ca/wp-content/uploads/2020/10/GiantHogweed_BMP.pdf

  • https://natureconservancy.ca/en/what-we-do/resource-centre/invasive-species/giant-hogweed.html

  • https://www.ontario.ca/document/weed-identification-guide-ontario-crops/giant-hogweed

  • https://www2.gnb.ca/content/dam/gnb/Departments/10/pdf/Agriculture/GiantHogweed.pdf

  • https://www2.gnb.ca/content/dam/gnb/Departments/10/pdf/Agriculture/GiantHogweed.pdf

  • https://www.quebec.ca/en/housing-territory/healthy-living-environment/identifying-and-getting-rid-of-giant-hogweed

1. Nicholas A. Page, Ronald E. Wall, Stephen J. Darbyshire, and Gerald A. Mulligan. 2006. The Biology of Invasive Alien Plants in Canada. 4. Heracleum mantegazzianum Sommier & Levier. Canadian Journal of Plant Science. 86(2): 569-589. https://doi.org/10.4141/P05-158
2. Trottier N, Groeneveld E, Lavoie C. Giant hogweed at its northern distribution limit in North America: Experiments for a better understanding of its dispersal dynamics along rivers. River Res Applic. 2017; 33: 1098–1106. https://doi.org/10.1002/rra.3149

Invasive Species Categories

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