Study

A review of the effectiveness of manual and mechanical methods for control of giant hogweed Heracleum mantegazzianum in Europe

  • Published source details Nielsen C., Ravn H.P., Nentwig W. & Wade M. (2005) The giant hogweed best practice manual. Guidelines for the management and control of an invasive weed in Europe. Forest & Landscape Denmark, Hoersholm.

Summary

Giant hogweed Heracleum mantegazzianum (native to eastern temperate Asia) is a tall perennial plant that is now widespread in many temperate areas of Europe. It has significantly increased its geographical range in recent years, being especially abundant along stream and river banks. Because of its tall height and that it often forms dense mono-species stands, giant hogweed often stifles out native plant communities.

A European Commission funded project was undertaken to provide scientifically-based guidelines for management and control in Europe of an invasive plant, giant hogweed Heracleum mantegazzianum, and two closely related species, H.sosnowski and H.persicum. As part of this project, the effectiveness of several manual and mechanical control techniques were reviewed, including ploughing, root cutting, stem cutting, mowing and umbel removal.

Ploughing: On agricultural land, deep ploughing (up to 24 cm) is an effective means of control. It significantly reduces hogweed seed germination as the upper soil (where the majority of the seeds are concentrated) is buried. Studies indicated that the best results were obtained if hogweed plants were cut or treated with herbicide, prior to ploughing.

Root cutting: Root cutting (usually performed with an ordinary spade with a sharpened blade and cut parts pulled out) is best undertaken in early spring and if regrowth appears, should be repeated in summer. Experience suggests that the main tap root should be cut 10-25 cm below soil level. The method is very effective but labour intensive (therefore potentially costly) and thus suitable only for single plants or small stands.

Mowing: Mechanical mowing e.g. using a flail mower, has been shown to be useful for clearing large areas of hogweed. Smaller stands can be strimmed or scythed. After cutting, there is rapid basal regrowth and mowing must be repeated 2-3 times during the growing season to reduce nutrient build up in the roots and to prevent flowering and seed-set. One cutting regime which appeared more efficient than others was to cut only the flowering plants at mid-flowering stage to prevent seed production. Repeating this cutting regime should with the least effort (in comparison with other cutting strategies) eradicate the population in a few years as the seed bank and recruitment dwindles.

Umbel removal: Removal of umbels can be as effective as cutting the whole plant, but often fails to prevent seed production due to vigorous regeneration and therefore necessitates several visits over the flowering season. Umbel removal is most effective when terminal umbels just start to flower. Even then, there is some regeneration and treated stands must be checked to prevent release of seeds produced by regeneration. Cut umbels must be collected and destroyed as if left on the ground seeds may ripen. It is recommended that this method only be considered as a control of hogweed stands where no other control has taken place earlier in the season. Stem-cutting, a similar technique to umbel removal, necessitates the same crucial timing due to the regrowth potential, otherwise the treatment must be repeated later in the season to prevent the seed from maturing.

Conclusions: One root cutting or ploughing treatment are both effective in controlling giant hogweed. Manual/mechanical control requires two to three treatments per year over several growing seasons to be effective, and is often labour intensive. Regardless of control method, the treatment of plants should commence early in the growing season.


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