English names: Giant hogweed (GB), Giant cow parsnip (US, CA)
Nordic names: Kæmpe-Bjørneklo (DK), Kaukaasianjättiputki (FI), Kjempebjørnekjeks (NO), Jättefloka, Jättebjörnloka (SE)
Heracleum mantegazzianum is an invasive plant which prefers rich and moist soil. It grows along stream banks and rivers, ditches, vacant farmland, riparian areas, residential properties and along railways and roads.
H. mantegazzianum is among the largest herbs in Europe, usually growing 2-3 m (but up to 4-5 m) high.
Stem: hollow, 5-10 cm in diameter, with dark reddish-purple spots and bristles.
Foliage: the compound leaves are deeply incised and can grow up to 3 m in length.
Flower: the inflorescence looks like a white umbrella due to thousands of tiny, white flowers. The white umbrella can be as large as 76 cm.
Fruit: the green oval fruit turns dry and hay-coloured with swollen brown oil canals. It contains one seed.
Heracleum mantegazzianum is native to Caucasus region of Eurasia. It has been introduced into Europe and North America as an ornamental. The plant is established in the Nordic and Baltic countries, with exception of Russia and Latvia.
A map can be downloaded from EPPO’s website. See instructions here.
H. mantegazzianum reproduces exclusively via seed and it can take three to four years to flower, this happens in mid-summer after rosette plants have accumulated sufficient energy reserve. Some plants die after flowering; others are short-lived perennials and flower for several years. The flowers are insect-pollinated and self-compatible. Seeds are produced in late summer. An average plant bears about 20,000 seeds and most of them are able to germinate, which indicates high reproductive potential of the plant. Seeds normally germinate in spring, before the native plants appear, after they have completed the period of dormancy, which is broken by cold and wet conditions. Seeds can remain viable in the soil for up to 10 years.
H. mantegazzianum is spread naturally by seeds, which can be dispersed by wind, water and human activity. Water is the major agent of local and long distance seed dispersal due to the capacity of the seed to float for up to three days. Human activities such as transportation of plants and seeds can also aid long-distance dispersal. H. mantegazzianum has been used in decorative arrangements, as a spice in Middle Eastern cooking, and it has been cultivated for its nectar by bee keepers in Europe and North America. Another important dispersal mechanism is the translocation of seed-contaminated soil by humans or animals.
Detection and inspection
Inspection should be made in mid-April through July in vacant lots, unmaintained urban open space as well as in ravines and near known infested localities. Follow-up inspection of the eradication area is very important, since the seeds can survive for many years in the soil.
H. mantegazzianum is considered easy to survey for due to its large size. However plants in the first year are more difficult to find. In nurseries and local plant areas the plant can be misidentified and sold as cow parsnip (Heracleum maximum).
Pest status and importance
H. mantegazzianum continues to be available as an ornamental, and seed may be a contaminant of food produce, so it is likely to spread further. It can cause ecological damage by establishing quickly and displacing other species, which may provoke erosion along the river banks. However, the main concern is the health hazards of this species. Skin contact with the watery sap, which contains furocoumarins, followed by exposure to sunlight causes serious skin irritation (phytophotodermatitis). Contact with eyes may cause blindness. A study on the economic impact of H. mantegazzianum performed in Germany showed that the country annually spends a lot of money on medical treatment and on keeping the plant under control.
Source of information
See further information here:
Author: Elise T. Yamamoto Buch
Editor: Dorthe Vestergaard