Most Unwanted: Giant hogweed
Heracleum mantegazzianum
Habitat: Terrestrial
Threat: Threatens river bank habitats and species
Status: Established
Giant hogweed is a well known non native species because of the threat it poses to human health, especially that of children. This species can cause extensive lesions or blisters in susceptible individuals that are very slow to heal. It is now widespread in Ireland and is also a concern to environmental managers due to the ecological impacts.
What is it?
This species is a member of the parsley or carrot family, Apiaceae. It is a large herbaceous plant that can grow up to 5 – 6 meters tall and can be either biennial or perennieal. Plants are generally capable of flowering and setting seed only once in a lifetime (termed monocarpic). The seeds produced are easily dispersed by wind, water, animal or human influence. The seeds can start to sprout in early spring and can continue to do so throughout the growing season. Seeds are known to be viable for several years. The tall stem produced is rigid and hollow, up to 10cm in diameter with purple blotches on the surface. The leaves are deeply lobed and sharply pointed with soft hairs appearing on the under surface. Flowers are white and borne in clusters on a large umbrella shaped head.
Impact
This species represents a public health hazard. The toxins in giant hogweeds sap react with sunlight/UV rays. When the sap produced comes in direct contact with the skin can cause the skin to blister.
This species has a high competitive advantage over native plants. It can out compete for space and resources by shading out native and desirable plants. There is also a loss in invertebrate diversity as the plants these animals depend on become scarcer.
Other impacts include a significant increase in riverbank erosion in winter as the leaves die back resulting in the soil becoming exposed to increased direct rainfall.
In summer time rights of way and access points for water users such as fishermen may become impassable due to high infestation rates of giant hogweed.
Where is it from?
Giant hogweed is native to Asia but is now invasive in North America, continental Europe and Britain.
Where are they in Ireland?
The species is wide spread throughout the island of Ireland.
How did it get here?
Initially the species was brought to Ireland as an ornamental plant of parks and gardens.
How are they spreading in Ireland
Natural dispersal of seeds.
Contaminant of soil.
What you can do
Individuals should avoid contact with the sap of this plant due to the risk of skin blistering and lesions.
If you wish to eradicate a small infestation, it is recommended that you dig out the whole plant before it begins to flower and set seed. You must also dig out the root of the plant.
Download the Best Practice Guidance Document for control of this species.
Report all sightings.
Additional reading
Habitas Invasive Alien Species in Northern Ireland
