Giant hogweed reaches a height of 3 to 5 m. The stem reaches a diameter of up to 10 cm, is strong, hollow and often speckled red. The leaves appear three- or five-parted with pinnately pointed sections, short hairy underneath and sometimes very large. The inflorescences (umbels) reach a diameter of 50-80 cm. The flower colors can be white or yellow-green. The plants bloom from June to August. The fruits are 10-14 mm long and 6-8 mm wide, with bristly hairy marginal ribs.
In Austria, the plant occurs preferentially at forest edges, in meadows, in the shore area of water bodies, on wasteland, but also in the garden. Giant hogweed originates from the Caucasus and grows there on forest edges and streams in areas up to 2,000 m above sea level and with sometimes high precipitation (2,000 mm). Mass populations do not exist in the original home of these plants.
Giant hogweed cultivated as a garden and ornamental plant, as well as a bee pasture. Reproduction of the plant occurs exclusively by seeds. A single plant can produce up to 50,000 seeds. Most seedlings are found less than 5-10 m from the mother plant. The seeds are spread by the wind no more than 100 m, but can also be spread over longer distances by flowing waters.
Giant hogweed has implications for human health. The whole plant, especially the sap, contains phototoxic furanocoumarins. Upon contact and exposure to sunlight, severe skin inflammation with severe blistering may develop after a short time. Giant hogweed probably has a minor impact on flora and vegetation. While perennials of these plants form very dense stands and shade the understory with their huge leaves, so that native vegetation can be displaced by lack of light, these are largely common species.
Positive effect: for many flower visitors, especially Hymenoptera, hoverflies and beetles, hogweed provides abundant food.
Prevention and control
- Individual plants or small stands can be dug up or pricked out in spring (mid-April at the latest) or in autumn (October to early November).
- At the beginning of fruiting maturity (end of July), the plant can be killed by mowing (brush cutter) or cutting off the inflorescence.
- Herbicides can be used against giant hogweed, preferably at the beginning of the growing season and in summer (only on land used for agriculture and forestry, see list of plant protection products approved in Austria).
- It is important to control small initial populations or individual plants to prevent further colonization of entire regions.
Nielsen, C., Ravn, H.P., Nentwig, W., Wade, M., 2005. practice guide giant hogweed - guidelines for management and control of an invasive plant species in Europe. Forest & Landscape Denmark.
Last updated: 05.09.2023