Identifying and managing Giant hogweed

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Scientific name: Heracleum mantegazzianum

Biennial plant (herb) in the Carrot family (Apiaceae)

Persian hogweed, a plant closely related to Giant hogweed (which is also an invasive plant in the UK) is a little bit different, as it is a long-lived (perennial), polycarpic (flowers many times) plant.

Dense seedling, first year (immature) and second year (mature) plants growth early in the growing season forms a dense, competitive groundcover restricting native plant access to space and light.

Giant hogweed produces phytotoxins (plant poisons) including furanocoumarins and related compounds which are contained in all parts of the plant to deter insect predators in the native range. When these phytotoxins come into direct contact with the skin of people (and some herbivores) and are exposed to light they cause phytophotodermatitis, which results in extensive blistering and scarring if exposure is significant (and particularly if treated incorrectly). It is important to note that initial contact is painless. In certain circumstances phytophotodermatitis may recur for several years following exposure.

How does Giant Hogweed grow and spread?

• Reaches up to 5.5m tall in full growth.
• Spreads rapidly by seed
• Two species of invasive hogweeds (Giant and Persian) present in
  the UK and Ireland

Where does Giant Hogweed grow?

Common habitats where Giant Hogweed is found include:

• Rivers and other watercourses
• Waste Ground
• Roadsides
• Railway embankments and cuttings
• Amenity areas
• Field margins

What impacts do these plants have?

Competitive growth of Giant hogweed growth has significant health implications, in addition to negative ecological and socioeconomic impacts which include:

• Human health and agriculture – plant poisons are toxic to humans and some livestock. Consequently, there is a future risk of civil litigation in circumstances where the plant has not been reported clearly, and subsequently controlled effectively and safely.
• High management costs – estimated at approximately £2.4 million per annum UK-wide.
• Reduced habitat availability and quality – reduction of native plant diversity.
• Limited soil binding capacity – following dormancy/death in late autumn, few native plants remain to protect the soil surface from heavy rainfall in the winter and spring months, increasing erosion risk.