Giant Hogweed Control in Ontario

What Is Giant Hogweed?

Giant hogweed is a very large member of the carrot family that can exceed four metres in height when flowering. It has thick hollow stems with coarse hairs and distinctive purple blotching, deeply incised leaves that may be a metre or more across, and large umbrella-shaped white flower clusters.

It is often confused with native cow parsnip and with other large white-flowered relatives. Because the management approach and the hazard level differ, identification should be confirmed before anyone approaches the plant closely.

Why Is Giant Hogweed a Problem?

Giant hogweed sap contains compounds that can make skin extremely sensitive to sunlight. Contact followed by sun exposure can cause severe burns, blistering and long-lasting skin discolouration, and sap in the eyes can cause serious injury. This makes it a direct health hazard rather than only an ecological one.

It also produces very large quantities of seed and forms dense patches that shade out other vegetation, and it spreads readily along watercourses, ditches and roadsides.

• Sap can cause severe skin reactions when exposed to sunlight
• Presents a hazard to workers, the public, children and pets
• Produces large quantities of seed that persist in the soil
• Forms dense patches that displace other vegetation
• Spreads along watercourses, ditches and disturbed corridors

Where Does It Commonly Grow?

Giant hogweed favours moist, disturbed ground: stream and river banks, ditches, roadsides, ravines, field edges and neglected areas. It is often introduced through ornamental planting and then spreads outward from the original site.

How Is Giant Hogweed Managed?

Management combines eliminating seed production with depleting the root system. Preventing plants from setting seed is a priority in any program, because the soil seed bank determines how many seasons of follow-up will be required.

Approaches may include targeted herbicide treatment where appropriate for the site, and in some situations root cutting or careful removal of flower heads before seed matures. All work requires appropriate personal protective equipment and handling procedures because of the contact hazard.

Because seed persists in the soil, sites are monitored and re-treated over several seasons until new emergence stops.

Why This Species Warrants Professional Handling

The combination of a serious contact hazard, a persistent seed bank and identification difficulty makes giant hogweed a poor candidate for landowner removal. Cutting or strimming is particularly hazardous because it disperses sap.

If you believe you have giant hogweed, do not touch it, keep people and animals away from the area, and arrange a professional assessment. If contact occurs, wash the area, keep it out of sunlight and seek medical advice.

Giant Hogweed Management in Northeastern and Central Ontario

Invasive Veg Solutions Inc. provides professional invasive vegetation management throughout Northeastern and Central Ontario, including municipal land, roadsides, natural areas and private property.

Where a hazardous species is present on a property that the public or work crews access, an assessment establishes the extent of the population, the hazard controls required and an appropriate multi-season management approach.