Taxonomy
Heracleum mantegazzianum | Giant Hogweed | Feabhrán capaill
Distribution
Status
Conservation status
Least Concern
Legal status
Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).
Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).
Regulated invasive species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].
First reported in the wild
pre-1866
Invasiveness
Invasive species - risk of High Impact
Irish status
Established
Introduction pathways - 1
Escape from Confinement
Introduction pathways subclass - 1
Ornamental purpose
Invasive score
19
NAPRA Ireland risk assessed
No
Species Biology
Identification
A tall perennial herb (living 3-5 years) with a pale yellow root. Has a single ridged stout hollow stem up to 10cm thick at the base and up to 5m tall, green with purple patches. Leaves are pinnately arranged (leaflets in opposite pairs with one terminal leaf) and large up to 2.5m across. Flowers are white (rarely pinkish), in umbells up to 80cm across (Tiley et al., 1996). It can have up to 50,000 seeds per plant that are 0.9-1.5cm long, flat, with oil ducts showing as dark stripes 2 on one side and 4 on the other side.
When fully grown it's 'giant' stature make it readily identifiable. It may be confused with the native Hogweed (Mantegazzianum sphondylium) but this species has a much thinner stem 1-2cm, leaves are not as sharply divided and it is rarely more than 2m tall. If Giant hogweed has been disturbed/trampled then it may not grow to such height but would still retain the large stem, leaf and umbel.
Ecology
Spreads by seed. After reaching maturity, it flowers, sets seed then dies. This can take 3-5 years. Can form extensive stands and as cover increases can decrease the number of vascular plant species per unit area (Thiele & Otte, 2007). Can cause erosion of river banks when the plant dies back during winter exposing bare soil (Caffrey, 1999) and soil influx into rivers can render gravel substrates unsuitable for salmonid spawning (Caffrey, 1999). May impact on human health as compounds in the sap can cause phytophotodermatitis within 24-48 hours after exposure, with symptoms including: mild to severe erythematours reactions (red colouring of the skin); blistering of the skin; and hyper-pigmentation of burned parts of the skin for months or years (Thiel & Otte, 2007).
Habitat
Mires, bogs & fens; Grasslands and landscapes dominated by forbs, mosses or lichens; Woodland, forest and other wooded land; Constructed, industrial or other artificial habitats; Regularly or recently cultivated agricultural, horticultural or domestic habitat
Reproduction
Flowers, generally after 3 years, producing large amounts of seed, estimated with estimates ranging from 5,000-29,000 seeds per plant, though the potential seed production may be as high as 100,000 per plant (Tiley et al., 1996).
Pathway and vector description
Popular Victorian garden 'curiosity', it was introduced to Britain and then Ireland in the 19th century (Reynolds, 2002). First noted escape from cultivation was in 1902-1903 in Dublin (Reynolds, 2002).
Mechanism of impact
Competition
Management approach
There is currently an EU wide ban on the sale, growing and keeping of this plant (European Commission, 2017). Protective clothing, face-masks and goggles, rubber boots and gloves must be worn by personnel involved in the control of this species (DARD, undated).
Public awareness
Education of the general public in identification of Heracleum mantegazzianum as well as its human health and ecological impacts would assist in early detection and reduce the number of contacts with the plants. Posters, leaflets, radio and online information would all be valuable. Signs declaring the presence of Giant hogweed and its possible health effects should be posted at infestations.
Manual
Hard to reach areas can be cut using scythes (Nielsen et al.,2005). H. mantegazzianum are monocarpic and usually flower at 3 or 4 years (Caffrey, 1999). Only cutting the flowering plants (during mid-flowering) will eradicate seed production and the plants will gradually shade each other out (Nielsen et al.,2005). This is much less labour intensive than other manual methods but should be effective within a few years.
Plants can be dug up using a sharp spade to slice diagonally through the root at least 15cm below soil level (DARD, undated). This should be done in early spring and again in mid-summer (Nielsen et al., 2005).
Mechanical
Deep ploughing (>24cm) is an effective way to control infestations on accessible land (DARD, undated; Nielsen et al.,2005). Nielsen et al. (2005) recommend first using a manual or chemical control to maximise effectiveness.
Chemical
Glyphosate and triclopyr can both be used for control. Triclopyr is selective for broadleaves but is not approved for use near water. Glyphosate is not selective but certain formulations are approved for use beside water. The first application should be made in early spring with a second application before the end of May (Nielsen et al.,2005). Eradication will require treatment for 4-5 years (DARD,undated).
A stem injection system specially developed for Hogweed is available. An applicator gun is used to inject one stem per plant 12 inches above the root crown. This eliminates herbicide contact with non-target species and can be carried out in inclement weather (DARD, undated). However, this method puts the operative at risk of having sap sprayed back at them when they remove the needle from the stem and health and safety must be made paramount during these treatments.
Environmental
Cattle and sheep readily eat H. mantegazzianum and grazing will gradually weaken and kill the plants (Nielsen et al., 2005). Stock should be monitored for signs of photosensitisation and digestive problems, which can result from the consumption of the furanocoumarins in the plants (DARD, undated). Dairy animals should not be used as the milk will have an unpleasant odour (DARD, undated). This method can eradicate an infestation within 5-10 years (DARD, undated).
Broad environment
Terrestrial
Habitat description
Found on riversides, roadsides, waste ground and former cultivated fields.
Species group
Plant
Native region
Temperate Asia
Similar species
Heracleum sosnowskyi, Heracleum persicum
Distribution
World distribution(GBIF)
Irish distribution
Established - Widespread. Locally abundant, naturalised and invasive (Reynolds, 2002), found along river banks and waste ground, favours damp ground (Reynolds, 2002). May occur initially as a single plant but due to large volumes of seeds produced can rapidly spread within an area (Tiley et al., 1996).
Native distribution
Native to the Caucasus (Tiley et al., 1996), the area between the Black and Caspian seas.
Temporal change
Date of first record category
Pre-1900
Fifty year date category
Unknown
Records submitted to Data Centre in 2024
The following map is interactive. If you would prefer to view it full screen then click here.
How can you help
Report any sightings to the National Biodiversity Data Centre
Further information
Delivering Alien Invasive Species In Europe (DAISIE) project list this as one of the 100 Worst Invaders in Europe.
Control and management guidance documents listed here but please note that advice should be sought on best control options for infestations in Ireland and more locally and especially in the use of herbicides.
Nielsen, C., H.P. Ravn, W. Nentwig and M. Wade (eds.), 2005. The Giant Hogweed Best Practice Manual. Guidelines for the management and control of an invasive weed in Europe. Forest & Landscape Denmark, Hoersholm, 44 pp. Available from: http://bit.ly/2vJEoPN [Accessed: 08/08/2017]
Giant hogweed (Heracleum mantegazzianum). Countryside Management Publications. Department of Agriculture and Rural Affairs. Available online: http://invasivespeciesireland.com/wp-content/uploads/2016/05/giant_hogweed-DARD-updated.pdf [Accessed: 08/08/2017]
References
Publications
Caffrey, J. M., & Madsen, J. D. (2001). The management of giant hogweed in an Irish river catchment. Journal of Aquatic Plant Management, 39, 28-33.
Caffrey, J.M. (1999) Phenology and long-term control of Heracleum mantegazzianum. Hydrobiologia 415, 223–228.
Department of Agriculture and Rural Development. (undated). Countryside Management Publications Giant Hogweed (Heracleum mantegazzianum). http://invasivespeciesireland.com/wp-content/uploads/2016/05/giant_hogweed-DARD-updated.pdf Site accessed 6 September 2017.
European Commission. (2017). Invasive Alien Species of Union Concern. European Union, Luxembourg.
Nielsen, C., H.P. Ravn, W. Nentwig and M. Wade (eds.), (2005). The Giant Hogweed Best Practice Manual. Guidelines for the management and control of an invasive weed in Europe. Forest & Landscape Denmark, Hoersholm, 44 pp http://labgis.ibot.cas.cz/wp-content/uploads/pdf/ Site accessed 6 September 2017.
Reynolds, S.C.P. (2002) A catalogue of alien plants in Ireland. National Botanic Gardens. Glasnevin, Dublin.
Thiele, J., & Otte, A. (2007). Impact of Heracleum mantegazzianum on invaded vegetation and human activities. In: Pysek P, Cock MJW, Nentwig W, Ravn HP (eds., 2007) Ecology and Management of Giant Hogweed (Heracleum mantegazzianum). CAB International, pp 144-156.
Tiley, G. E. D., Dodd, F. S., & Wade, P. M. (1996). Heracleum mantegazzianum Sommier & Levier. Journal of Ecology, 297-319.