Giant hogweed is harmful to health and the environment. It hampers the growth of other plants in the habitats it colonizes. It destabilizes ecosystems and contributes to bank erosion. It should never be seeded, planted, propagated or transported. Contact with its sap can cause painful skin reactions similar to burns. If required to handle it, you should wear gloves, long pants, and long sleeves.

Description of the plant

Giant hogweed (Heracleum mantegazzianum) is a poisonous, invasive, exotic species. It is a perennial in the carrot and parsnip family like cow parsnip, which it resembles, although it is much less poisonous. Giant hogweed can measure from two to five meters high, or thirty centimetres to one meter after mowing. Its very robust stem is covered with stiff white hairs and numerous, very distinct, extensive, raspberry-red to purple spots. Its leaves can be up to 1.5 meters wide and three meters long.
Giant hogweed is a spectacular, impressive plant. It is also very appealing and intriguing. Children may hide or play in it, or use the stem as a flute, peashooter, or telescope. Adults may appreciate it as an ornamental plant.

hogweedHabitats colonized by the plant

Giant hogweed first appeared in Québec in 1990. It has been found in a number of regions in the province, including Bas-Saint-Laurent, Capitale-Nationale, Côte-Nord, Chaudière-Appalaches, Gaspésie–Îles-de-la-Madeleine, and Lanaudière.
Giant hogweed prefers cool, damp habitats and is found in the following types of disturbed habitat: Along the banks of waterways, in ditches, along railways, on roadsides, in fields and in vacant lots.

Health effects

Although contact with the sap is not painful in itself, the toxins it contains are activated by light (UV rays), making the skin extremely sensitive to sunlight and causing a type of damage to superficial skin cells called phytophotodermatites.
Phytophotodermatites can develop up to 48 hours after exposure to sap. It is characterized by localized rash and oedema (red, swollen skin), blisters, or even burns. Once healed (in approximately a week), brown spots can persist and the affected region can remain sensitive to sunlight for several months.
All parts of the body can be affected, but the back of the hands, arms, legs, and face are the most commonly injured because they are more likely to be exposed to the poisonous sap and to sunlight.

The risk of exposure is high for the following groups of people:

  • Children and their parents
  • Horticulturalists
  • Farmers
  • Personnel doing brushing work
  • Anyone living or spending time in areas where the plant is found.

To reduce the risk of exposure to the sap, these individuals should be able to recognize giant hogweed.

What to do in the event of exposure
If your skin has been in contact with sap

  • Remove the sap as quickly as possible without spreading it. Use a sheet of absorbent paper and do not rub. Wash the affected area with soap and rinse thoroughly with water. Then wash your hands.
  • Change and wash your clothes to avoid contaminating other parts of your body or other people.
  • Cover affected areas (gloves, long pants, and long sleeves) to avoid exposing them to light (including artificial light) for at least 48 hours.

If your eyes have come in contact with sap

  • Rinse your eyes thoroughly with clean water for ten minutes.
  • Wear dark sunglasses to avoid exposing your eyes to light.
  • See a doctor as soon as possible.

If you have burns

  • Avoid any exposure to sunlight for at least a week.
  • Use sunscreen for six months.
  • Call the Info-Santé helpline at 8-1-1 for more information on how to treat burns.

If you think you have been in contact with giant hogweed or if you would like more information on what to do in case of burns, contact Centre antipoison du Québec at 1-800-463-5060 or the Info-Santé help line at 8-1-1.

You should see a doctor in the following cases:

  • A child is affected;
  • Eyes are affected;
  • The affected person is running a fever;
  • Large lesions develop;
  • Red, swollen skin over an area greater than one-third of the affected body part; Presence of blisters 25 millimeters or more in diameter (larger than a quarter); Several affected body parts;
  • Pus (yellow opaque liquid) in the wounds.

hogweed-1How to control it

Giant hogweed should be controlled to protect not only public health, but also the environment for the following reasons:

  • It disrupts the balance of the ecosystems it invades.
  • It reduces biodiversity.
  • It promotes bank erosion.

It is very important to limit its spread by avoiding seeding, planting, propagating, or transporting it. As far as possible, it should be eliminated and its regrowth prevented.

hogweed-3If you must handle the plant, protect yourself:

  • Cover your body head to toe with protective, nonabsorbent clothing (synthetic, waterproof material): long pants, long sleeves, and waterproof gloves with long cuffs.
  • Pay special attention to areas where your protective clothes overlap (wrists, ankles, neck).
  • Remove your clothes and gloves by turning them inside out. To prevent contamination, avoid putting soiled clothes in contact with other objects or clothing and wash them well before any further use.
  • Protect your eyes or, even better, your entire face (visor).
  • If you are mechanically cutting the plant, make sure that no one is standing where they could be hit by the sap or plant debris thrown off during mowing or cutting. Use a knife or round shovel to cut stems and roots.
  • Wash tools that have been in contact with sap (pruning shears, brush cutter, etc.).
  • Wash your hands and face.

Source : ministère de la Santé et des Services sociaux.

For more information on controlling giant hogweed, contact Centre d’information du ministère du Développement durable, de l’Environnement et des Parcs:

  • Telephone: 418-521-3830 (Québec City) or 1-800-561-1616
  • Fax: 418-646-5974
  • Email: info@mddep.gouv.qc.ca