Giant Hogweed

Common name:  Giant Hogweed
(also known as Wild rhubarb, cartwheel flower, wild parsnip)
Scientific name:  Heracleum mantegazzianum
Management programme:  Organism of Interest (OOI)

Why is it a pest?

Giant hogweed is poisonous to humans and care should be taken when removing this plant. Exposure to dust or sap can cause skin irritation, blistering, swelling, and long-term scaring. If a person gets the sap in their eyes, it can cause temporary or permanent blindness.

A single plant can produce up to 50,000 seeds and these spread rapidly via water courses. Plants can form dense colonies that suppress native vegetation and when it dies down during winter, it can leave infested banks bare of vegetation and susceptible to erosion or reinvasion by other pest species.

What does it look like?

Giant Hogweed is a perennial herb (plant with a life cycle of three or more years) that can grow up to 6 meters tall and has serrated leaves up to 50-100 cm long. The leaves form a rosette at the base and grooved, hollow stems are spotted reddish purple with sturdy bristles containing toxic sap. Plants form forked branches with large umbrella-like clusters of greenish-white flowers in summer, followed by dry, flattened, oval light brown fruit (1cm long).

When can I spot it best?

Between December and February is the best time to spot giant hogweed as it is flowering and fruiting.

Where does it grow?

Giant hogweed has been recorded in coastal Otago from Oamaru to the Catlins and in the Central Otago (see map).

Giant hogweed typically grows in rich, moist soils and around water ways.

What are the rules?

There are no specific rules associated with Giant Hogweed as it is an organism of interest in the Otago Regional Council’s Regional Pest Management Plan (2019-2029).

How can I control it?


Wear protective gear to cover your arms, hands and eyes. If you get dust or sap on your skin, wash the area immediately.

Removal options include:

  • Pull the whole plant our before it seeds in spring/summer.
  • Cut stems below ground level in summer and spray any re-growth with glyphosate as required.
  • Spray the whole plant with glyphosate in spring, and again in summer if required.

Be aware, seeds can remain dormant for up to 5 years. To effectively control this pest, continue to monitor the site and consider planting native species, as these can prevent giant hogweed from growing back again. To find native planting advice visit Otago Native Planting Guide.

Management programme