skip to main content
Flood Status
Low Water Status


Invasive Species

Invasive Species

While there are many websites that now specialize in introduced or invasive species, the purpose of this page is to provide you with information about major, nuisance or toxic species within our jurisdiction.

Giant Hogweed (Heracleum mantegazzianum)

Giant Hogweed is a plant native to Southwestern Asia.  It belongs to the carrot family and is closely related to Cow Parsnip, the only hogweed genus native to North America.

Giant Hogweed was first introduced to North America in the early 1900s and since then has spread widely.  It was first confirmed in Ontario in 1949.  It is a biennial plant producing large leaves during the first year of growth and a flowering stock the second year (typically).  The flowers are large umbrella shaped clusters and bloom from June to August.  A single plant can produce up to 100,000 seeds.  The leaves of Giant Hogweed are large, deeply incised, pointed and serrated.  The stem is hairy and hollow with purple splotches.

Giant Hogweed can grow up to 1.5m tall or well over 6 feet tall (photo above).

NOTE: Giant Hogweed is a dangerous plant. The sap of this plant contains toxins that increases the skin's sensitivity to light. This can result in severe burns, blisters and temporary or permanent blindness.  Do Not Touch This Plant! Please  make sure that children are not playing around this plant.

Safety Tips for Working Around and or Controlling Giant Hogweed

  • wear gloves, a mask and safety helmet with face shield if undertaking any work with this plant
  • cover up affected areas right away (keeping out of the sunlight). Wash affected skin and/or clothing immediately after working with or coming in contact with this plant.
  • wear full-length clothing and closed toed shoes, being extremely careful not touch any part of the plant with bare skin
  • do not burn this plant as a means of control
  • use soap and water to wash down equipment and other tools that may have come in contact with this plant
  • weed-whackers should not be used to control this plant.  Toxic sap may spray outward exposing the operator and or nearby people
  • mowing may work if plants are young, however, this should be continued on a regular basis as the plants will tend to sprout from the root stalk.  Continued mowing will eventually decrease the plant's energy and food storage.
  • small infestations can be hand-pulled or dug up, making sure to use the safety measures above.
  • Large infestations can be treated with Roundup.  You are allowed to use Roundup to control poisonous plants on your own property. An initial application is best made between April and early June. To minimize impact, spray only when there is no wind and avoid spraying around water! Follow all herbicide directions.
  • monitor the same location for a few years afterwards.  Seeds can stay viable in the soil for between 7 - 15 years.


  1. Ontario's Invading Species
  2. Ministry of Natural Resources and Forestry - Hogweed Fact Sheet
  3. Invasive Species Centre of Canada
  4. Early Detection and Distribution Mapping System
  5. How You Can Combat Invasive Species
  6. See it, Map it!
  7. Saugeen Watershed Invasive Species List












© 2021 SVCA

Web Site by Websmart Inc