Giant hogweed

Giant hogweed is a biennial or perennial megaherb that grows to six metres tall. It can cause permanent damage if touched or ingested.

Description

• Taproot is forked or branched and fibrous.

• Stems are hollow, finely haired and covered in red/purple spots.

• Leaves are large (50cm–100cm long), deeply divided into 3 leaflets, forming a rosette at the base.

• Flowers are small, green/white and appear on tall flowerstalks on umbrella-like clusters.

• Seeds dispersed by water, gravity and wind.

• Habitats include riparian and forest margin, roadsides, flood plains, and drains.

What you need to know

Giant hogweed forms dense infestations, suppressing native vegetation and exposing banks to erosion during periods of seasonal dieback. Can cause photodermatitis in humans.

Poison advice

Giant hogweed is poisonous to humans. Either touching it, or exposure to dust from weed-eating, can irritate skin and cause blisters and swelling. The sap from leaves and stems is highly toxic and can cause 'photodermatitis' or 'photosensitivity' where the skin becomes very sensitive to sunlight and may suffer blistering, pigmentation and long-lasting scars. Contact with the eyes can lead to temporary or permanent blindness.

Body parts that come into contact with giant hogweed should be washed immediately and protected from direct sunlight. Contact your local poison information centre on 0800 POISON (0800 764 766) or your local vet.

Management approach

Giant hogweed is declared an unwanted organism by the Ministry for Primary Industries (MPI) because it is capable of causing harm to the natural environment, physical resources or human health in Aotearoa/New Zealand.

These species pose a high risk to our environment, economy, recreation, and cultural values.

Rules

Any species declared a pest, including unwanted organisms, cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, or multiplied, communicated, released, or cause to be released, or otherwise spread.

Control

Physical control

Take extreme care when controlling giant hogweed. Always wear gloves and eye protection and cover exposed legs and arms. Contaminated clothing and tools should be cleaned thoroughly. Wash any skin that comes into contact with plant material immediately and protect from the sun.

Dig or pull-out small plants or seedlings

Plant parts requiring disposal: all parts

Contact your local council for appropriate disposal locations

Chemical control

Cut plant close to the ground and immediately treat the stump with herbicide gel containing glyphosate.

Foliar spray with 20ml glyphosate plus 2ml penetrant per 1L of water.