Photo credit: @GBNNSS
Heracleum mantegazzianum - Giant hogweed
- Bogs, fens, grasslands, woodland, urban, agricultural and horticultural areas, riparian zones
- Tall perennial herb (3-5m) with a pale yellow root. Stem is hollow and is green with purple patches; the flowers are white and in umbels up to 80cm across. 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.
- Origin and Distribution:
- Giant hogweed is native to Asia but is now invasive in North America, continental Europe and Britain
- 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 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.
- Is it found in Ireland?: Yes. The species is widespread throughout the island of Ireland. More information can be found at NBDC and NBN Atlas NI.
- 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.
- NIEA Information and Identification Guide
- NIEA Signage
- NBDC Information and Identification Guide
- GBNNSS ID Guide
- The Giant Hogweed Best Practice Manual - 'Guidelines for the management and control of an invasive weed in Europe'
- NOBANIS Fact Sheet
- Property Care Association Guidance
- 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
- 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.