Giant hogweed

Heracleum mantegazzianum

Overview

Photo credit: ©GBNNSS
Heracleum mantegazzianum - Giant hogweed
Widely Spread Species:
  • Under Article 19 of Invasive Alien Species Regulation (1143/2014) Giant hogweed has been identified as a Widely Spread Species in Northern Ireland and as such, management measures have been put in place to minimise its impacts.

Habitat:
  • It is found in bogs, fens, grasslands, woodland, urban, agricultural and horticultural areas, and riparian zones.

  • Description:
  • It is a tall perennial herb (3-5m) with a pale yellow root. Its stem is hollow and is green with purple patches; the flowers are white and in umbels up to 80cm across. Its leaves are large (up to 2.5m across), and are in opposite pairs with a terminal leaf. It can produce up to 50,000 seeds per year.  It usually produces seeds before dying each year.

    Download N.I.E.A. ID guide

   
Origin and Distribution:
  • Giant hogweed is native to Asia but is now invasive in North America, continental Europe, Great Britain and Ireland.

Potential/Known impacts:
  • 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 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.
  • It is also harmful to human health as it produces sap that causes severe burns that will blister in the sun for many years.

How did it get here:
  • Initially the species was brought to the island of Ireland as an ornamental plant of parks and gardens. Its seeds can travel on the wind and in water, meaning that it can travel relatively easily in the right conditions. It may be unintentionally spread further by though contaminated soil.

Is it found in Ireland or Northern Ireland?:
  • It is present and widespread across Ireland and Northern Ireland.
  • More information can be found at NBDC and NBN Atlas NI.

Static Distribution Map as of Distribution - Courtesy of CEDaR


Manual Method for prevention:
  • Hand cutting should never be undertaken unless the operator is wearing full protective clothing to prevent skin contamination by the sap.
  • Infestations need to be controlled by digging out the whole plant as cutting through the stem must be done below ground level to ensure damage to the rootstock and to prevent regrowth from the base.
  • This is known as 'tap rooting' (see images below)
  • Cut the taproot approximately six inches below ground level using a spade, shovel, or anything with a large sharp edge. In areas with erosion or on steep inclines (where additional soil may be covering the plant base), plants may need to be cut up to ten inches below the soil.
 
When cutting the root you need to separate the thick stem base bearing old leaf scars from the root below. If possible (for your safety), cut the plants before the leaves are very large. The cut part of the plants should be removed from the soil and left out to dry (safest for control person) or bagged and disposed of. Survey the site for up to 7 years after the last growth as remaining seeds may be viable and regrow.    

 

More Methods to Prevent Spread

 

  • Promote native species and biodiversity - use alternative, native plants
  • Know what you are buying/growing and source native Irish seed and plants
  • Do not swap plants and cuttings
  • Clean plants before adding to ponds (dispose of water away from water courses)
  • Follow control advice and watch out for hitchhikers - inspect new imported purchases for invasive pest and pathogens
  • Never collect plants from the wild
  • Safe disposal of plant material and growing media
  • Record via CEDaR

BE PLANT WISE!!

Download these posters and promote in your area.
 
Current Legislative Position (Listed on 02 August 2017) This species must not intentionally be brought into the Union; kept; bred; transported to, from or within the United Kingdom, unless for the transportation to facilities in the context of eradication; placed on the market; used or exchanged; permitted to reproduce, grown or cultivated; or released into the environment. For further queries, you can contact the Non Native Invasive Species Team in the Northern Ireland Environment Agency on 028 9056 9558.  

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland