Giant Hogweed

You are here

Giant Hogweed is an invasive, non-native plant that poses a serious threat to human health and natural ecosystems.

Some of the chracteristics are:

  • It can reach up to 6 metres in height
  • It has hollow stems that may be 5 to 10 centimetres in diameter with dark red-purple splotches and coarse white hair
  • The leaves of the plant can grow over 1 metre in width and have hairs on the underside
  • The plant also produces flattened oval shaped fruit and numerous white flowers clustered in an umbrella shape form
  • Giant Hogweed is sometimes confused with similar harmless plants such as cow parsnip, angelica and Queen Anne's lace

What are the human health risks?

  • A clear and watery sap is found in the stem and hairs of Giant Hogweed. Contact with the sap can cause a skin reaction whereby skin becomes sensitive to the ultraviolet light in the sun light.
  • Reactions can occur up to 48 hours after contact, and sensitivity can lead to painful blisters and burns. The affected skin may remain sensitive to ultraviolet light for years.
  • Blisters can lead to pigmented purple and black scars that may last for long periods and may be permanent.
  • Contact with the eyes can cause temporary and sometimes permanent blindness.
  • Unfortunately, children are the most likely to get hurt by Giant Hogweed because they don't know the risks.

What are the effects to the eco system?

Giant Hogweed is an aggressive competitor, able to out-compete native plant species reducing the amount of suitable habitat available for insects, birds and mammals.

Where can it be found?

Giant Hogweed is native to the Caucasus Mountains and Southwestern Asia. It was introduced as an ornamental plant into Europe and has since spread to Canada and the United States. It can be found throughout Southern Ontario. In York Region, isolated plants have been found in Jackson's Point on properties on Lake Drive East, Hoffman Drive, and on Malone Street. A single strand of Giant Hogweed has been found in the laneway between High Street and North Street in Sutton.

What are the control measures of Giant Hogweed?

Giant Hogweed is very difficult to eradicate. The average Giant Hogweed plant produces approximately 20,000 seeds but individual plants have been reported with over 100,000 seeds. The reproductive nature of these plants is enormous. The seeds can lay dormant in the soil for up to 15 years. Individual plants can live up to 12 years. They bear seeds once but due to the high volume of seeds, Gaint Hogweed can survive in an area for many years. Seeds produced by self-pollination are viable; more than half of them germinate and give rise to healthy seedlings. This means that even a single isolated plant, resulting from a long distance dispersal event, is capable of founding a new population.

How can Giant Hogweed be eradicated?

To remove Giant Hogweed the person should take the following precautions:
  • Wear water-resistant protective clothing covering as much of your body as possible including safety boots, neoprene gloves, safety eye goggles and a full face shield.
  • Do not get any sap on your skin.
  • Immediately remove any flower heads to prevent seed growth and dispersal.
  • Sever the plant roots 8 to 12 centimetres below the soil surface.
  • Dispose of all plant parts in double-bagged clear garbage bags, seal the bag and let it sit in the sun for 3 to 4 weeks to destroy the seeds and roots. These bags should then be sent to the landfill.
  • Spray the roots remaining with an appropriate pesticide.
  • Return to the plant site periodically to remove any new plant growth.
  • Ensure the cutting device used and any protective clothing is washed thoroughly or disposed safely.

If exposed to Giant Hogweed

  • Wash the affected area thoroughly with water and soap
  • Avoid exposure to sunlight
  • Seek medical attention

For additional information, please visit: