Giant Hogweed

Most people know about poison ivy, but there is a new, much more poisonous plant invading Ontario's outdoors and putting workers at risk. It's called giant hogweed.

Use this article as a safety talk to inform your outdoor workers about the hazards.


What does it look like?

Giant hogweed is a tall plant that grows up to an astonishing five metres high. Small whisker-like hairs and reddish-purple spots cover its stem. From June to August, it produces a white flower that resembles an umbrella and can stretch one metre wide.

Various parts of the plant (including stems and leaves) release a clear watery sap that is extremely toxic.

Who is at risk?

Outdoor workers in southern Ontario can encounter giant hogweed near roadsides, streams, vacant lots, and waste areas.


How can it hurt you?

Giant hogweed is very poisonous:

  • Skin contact with the sap in the presence of UV light (such as sunlight) can cause swelling, itching, and blistering that lasts for months. Some people then become sensitive to UV light and experience a skin-color change that can last for years.
  • If the sap gets into your eyes, it can cause permanent blindness.

How can we control the hazard?

Employers and supervisors

Before work starts, notify workers about giant hogweed in the area and how it can hurt them.


Workers and others

  • Never touch or brush up against the plant with bare skin.
  • If you must work near the plant, cover all body parts using impermeable coveralls, gloves, and a face shield to protect the eyes and face.
  • Avoid using power tools near the plant because breaking or crushing the stem or leaves can release the toxic sap.
  • The only person that should remove a plant is someone who knows
    • the hazards
    • what controls will prevent contact
    • how to prevent dispersal of the plant (seeds scattering and later growing into full-grown plants).

What do I do if I'm exposed?

  • Wash the affected area immediately with soap and water.
  • Stay out of sunlight and cover up exposed areas.
  • Get medical attention immediately.

Where can I get more resources and info?

A Giant Hogweed Poster is available to download for free at

For more information, contact IHSA or Ontario's Ministry of Agriculture, Food and Rural Affairs at 1-877-424-1300.