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Giant hogweed (Heracleum mantegazzianum)

Giant hogweed is not established as a weed in Australia, but has been recorded in South Australia and Tasmania and is considered a potential weed threat. It could form dense stands that out-compete native plants, and its sap can cause severe skin injury to people.

Key facts

Type: Weed, herb.

Native to: Caucasus Mountains of south-west Asia.

Established in: .

Other names: Cartwheel Flower, Wild Parsnip, Wild Rhubarb, Giant Bearclaw.

Best time to act: Look for plants and treat them while young and rosetted, early in the growing season and before they flower or set seed.

Identification

  • This short-lived perennial herb usually grows 3 to 4 metres tall, but can reach 7 metres.
  • Its deeply divided, toothed leaves can grow up to 3 metres long and 1.5 metres wide, and resemble rhubarb leaves.
  • The leaf undersides, leaf stalks and hollow, ridged stems have bristles; stems also have dark reddish-purple blotches.
  • Mature plants produce broad, umbrella-shaped groups of small white flowers, up to 800 millimetres across.
  • Look-alike: Hemlock (Conium maculatum) is similar, but does not grow as tall and has more finely divided leaves.

Where it grows

In Australia it has been recorded in the Adelaide area of South Australia and near Devonport in northern Tasmania, where it appears to have been eradicated.

Why it matters

  • Sap can make skin highly sensitive to ultraviolet light, causing severe burns, swelling and painful blisters.
  • In Europe it competes aggressively with native plants and reduces habitat available to insects, birds and mammals.
  • When plants die back in winter, bare ground can contribute to erosion on riverbanks and steep slopes.
  • Dense stands can obstruct access to amenity areas and riverbanks, reduce roadside visibility and lower recreational value.

How it spreads

  • It can regrow from underground buds on the crown and tuberous roots, and also spreads by seed.
  • Seeds can be carried by water, wind and birds, and spread by people through the ornamental plant trade, garden-waste dumping and the spice trade.
  • Seeds can stick to vehicles, clothing and animal fur, or be moved in contaminated soil.

Control options

  • Treat young rosettes before flowering and seed set; use registered herbicides during the growing season when green leaves are present.
  • Remove small plants with full personal protective equipment, avoiding contact with skin and eyes, and remove all roots and underground buds.
  • Cutting alone does not provide long-term control and can lead to rapid regrowth; treat regrowth with an appropriate registered herbicide.
  • Plan repeated follow-up for several years, as seeds can remain in the soil and plants may be difficult to eradicate.

Hygiene and washdown

  • Check and clean vehicles, clothing and equipment that may have picked up seeds, and avoid moving soil contaminated with giant hogweed seeds.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Declared pest (C1), prohibited. C1 Exclusion: to be kept out of WA, or out of the parts of WA where it is not established. Report any sighting to DPIRD. It must not be brought into WA (prohibited organism).
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

Sources