Giant Hogweed

Fact Sheet Adobe Portable Document Format (PDF)

Giant hogweed is found across southern Ontario and is becoming more common in Halton Region with numerous sightings reported each year.

Photos courtesy: Michael Cowbrough, Chief Weed Inspector, Province of Ontario

What is giant hogweed?

Giant hogweed is an invasive plant known for its enormous size.
- It can grow from 8 – 14 feet high (2.5 – 4 metres).
- The leaves of the plant can grow to 3 feet (1 metre) in width and have hairs on the underside.
The plant has hollow stems with dark reddish-purple splotches and coarse white hair.
The plant produces flattened oval shaped fruit and in the summer, small white flowers form.

It can be found along:
- roadsides
- vacant lots
- stream banks
- backyards
In Halton Region, it is most widely distributed along Sixteen Mile Creek and Bronte Creek.
Giant hogweed is native to Asia but has been introduced to North America as an ornamental plant.

Yes, a clear watery sap is found in the stem and hairs of giant hogweed.
- Contact with sap can cause a skin reaction where skin becomes sensitive to the ultraviolet light in sunlight.
Reactions will depend on the sensitivity of the individual and can lead to painful:
- Blisters - can lead to purple and black scars that may last for long periods
- Burns
- Temporary/permanent blindness if sap comes into contact with eyes.
Heat and moisture (sweat) can enhance the skin reaction.
Reactions can occur up to 48 hours after contact.

Yes, these include:
- Cow Parsnip
- Purple-Stemmed Angelica
- Spotted Waterhemlock
- Poison Hemlock
- Wild Parsnip
Halton Region is home to many native plants that resemble giant hogweed but do not pose the same health risk.
If in doubt, always confirm plant identification with an expert.

No by-law:
- Halton Region
- Milton
- Oakville
By-law:
- Halton Hills has included giant hogweed as a 'Nuisance Weed' under their Community Standards By-law (No. 2008-0138).
- Burlington has included giant hogweed as a "Noxious Weed" under "Schedule A" of their Lot Maintenance By-law (12-2011)
In Ontario, 24 weeds including giant hogweed are considered noxious under the Provincial Weed Control Act (R.R.O. 1990, Reg. 1096).

Yes.
Pesticides can be used to control plants that are poisonous to touch, such as:
- Poison Ivy
- Giant hogweed
There is a limit to its effectiveness as birds and water can carry the seeds to other locations.

Photos courtesy: Michael Cowbrough, Chief Weed Inspector, Province of Ontario

Do not touch! Keep children and pets away from the area.
Contact a licensed weed exterminator.
- Look under “Weed Control Service” in the yellow pages.
Professional staff at your local garden centre may also advise on products and methods to use for control of giant hogweed.

For your own safety, contact a licensed weed exterminator.
- Look under “Weed Control Service” in the yellow pages.
Pulling or cutting giant hogweed can be very dangerous as the plant is juicy with sap, which can become airborne when released.
If you do choose to remove giant hogweed, it is very important to do the following:
- Avoid any contact with skin
- Wear synthetic, water-proof clothing: long sleeves, boots, gloves, face protection and eye goggles
- Remove any flower heads to prevent seed growth and dispersal
- Remove the full rootstalk. Cut roots 8-12 cm below soil surface
- Wash your clothes afterwards!
Do not mow giant hogweed. This can stimulate budding on the rootstalk and risks exposure to the toxic sap.

If any sap reaches your skin, you must wash it immediately with cool, soapy running water.
Avoid exposure to the sun for at least 48 hours after contact. This is important since the sap increases photosensitivity of the skin.
Contact a medical professional as soon as possible for additional advice and treatment.

For your own safety, contact a licensed weed exterminator.
- Look under “Weed Control Service” in the yellow pages.
If you have removed the plant yourself:
- Place all parts in a plastic bag and leave in the sun for 3 – 4 weeks (to destroy seeds and roots).
- Garbage bags containing giant hogweed can be taken to the Halton Waste Management Site, however prior approval is required.
  - Dial 311 to make arrangements.
  - Regular disposal fees apply.
- Do not:
  - compost the plants
  - place curbside as Yard Waste
  - place curbside for GreenCart collection
  - place curbside for Garbage collection

If you see giant hogweed on Town or City property, please call your local area municipality.
- City of Burlington: 905-335-7600
- Town of Halton Hills: 905-873-2601
- Town of Milton: 905-878-7252
- Town of Oakville: 905-845-6601