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Dr. Andreas Hahn

LWF

Bavarian State Institute of Forestry
Section Forest Protection
Hans-Carl-von-Carlowitz-Pl. 1
D-85354 Freising

Phone: +49 (8161) / 4591 - 501
Fax:      +49 (8161) / 4591 - 900

Article

Author(s): Sebastian Werner; Translation Carolin Mößnang
Editorial office: LWF, Germany
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A dangerous beauty with toxic fibres – the Giant Hogweed

Blütenstand Riesenbärenklau
Abb. 1: The impressive flower of the Giant Hogweed (Heracleum mantegazzianum).

The Giant Hogweed (Heracleum mantegazzianum) is one of the most striking neophytes: an enormous white umbel, exemplars reaching a height of four meters, and big sawed leaves. At the end of the 19th century, this mountainous plant from the Caucasus was imported to Europe as an ornamental plant. Since then, it keeps spreading massively in our regions in gravel pits and fallow grounds, along streets, creeks, forest margins etc.

All parts of this plant contain the toxic substance Furocumarin. Intensified by solar radiation, coming in contact with this plant can lead to heavy allergic reactions with long-lasting burning scars. By the way, some bee-farmers appreciate the Giant Hogweed because of the rich flowering, but apart from them, nobody else does.

For years now, the "Kreisgruppe Starnberg" of the "Landesbund für Vogelschutz" has been implementing suppression measures against the Giant Hogweed and wants to profit from their experience to give some advice:

Measures for controlling the Giant Hogweed are supposed to fail if they are not planned in a consequent and adaptive manner and they shouldn’t be seen as a singular action. Long-sleeved protective clothing, gloves and a brimmed hat are absolutely necessary. The author once wiped his front with a glove after touching a Giant Hogweed – even this turned out to be a big fault!

Planning:

  • It has to be ensured that controlling measures are carried out regularly for at least five years.
  • Young standings which are still in development have to be the focus of attention.
  • You should concentrate on shores of rivers and lakes (beginning at the upper course), on the environs of biotopes, the occurrence of endangered species, frequented paths and playing grounds.

Methods:

  • Sustainable: Digging up the young plant in the second half of the month of April, using the planting mattock. The root of the Giant Hogweed tapes off and shows lots of lateral fibres which don’t have to be removed entirely. Problem: a lengthy procedure.
  • Specific: After the seed production in its second year, the Giant Hogweed withers! Thus, cutting off the umbel in time ( that is when seed production starts ) is a medium-term remedy. The umbels have to be removed because they would after-ripe. So it all depends on the right moment! Cutting too early can lead to re-inflorescence, cutting too late involves a certain risk of seed-dispersion while doing so.
  • Controversial: The elimination of larger stands is only effective if herbicides are used (painting the leaves in springtime or injection of the herbicide). Problem: not applicable in protectorates.
  • Damage limiting procedure: repeated mowing can impede seed production, but the plants keep sprouting after each cut.
  • Counterproductive: rotary cultivation and other forms of scarification improve the germinating capacity of the seed.

Further advice:

  • Warning signs should be posted in concerned regions to avoid compensation demands of others in case of damage.