Giant Hogweed (Heracleum mantegazzianum)

Species

Distribution


Giant hogweed
(Heracleum mantegazzianum)
Photo courtesy of Richie Miller DBIT


To view NBN location data click here

Impacts

Pathways
  • Out competes native vegetation for space and resources shading out desirable vegetation.
  • This results in loss of plant and invertebrate diversity.
  • Winter dieback increases exposes bare soil to direct rainfall and floods. Death of stem loosens surrounding soil that in high density stands can result in whole sections of riverbank being washed out.
  • Giant Hogweed is a public health hazard as the toxins in the sap react with sunlight/UV ray causing the skin to blister and severe scarring.
  • Can block access and rights of way
  • Seed dispersal particularly by water
  • Transport of contaminated soils.

Management

Prevention

Do not dump contaminated soil or plant fragments, dispose of them according to the Waste Management Licensing Regulations 1994. These define the licensing requirements which include “waste relevant objectives”. These require that waste is recovered or disposed of “without endangering human health and without using processes or methods which could harm the environment”. When leaving contaminated areas please check clothes, equipment and vehicles for plant fragments and/or contaminated soil. Refrain from using as an ornamental plant in gardens.

WARNING

The sap of giant hogweed contains a toxic chemical which sensitises the skin and leads to severe blistering when exposed to sunlight.

THIS REACTION CAN RECUR FOR MANY YEARS.

Physical Control

Should by hand or machine cutting never be undertaken unless the operator is wearing full protective clothing to prevent skin contamination by the sap. Cutting after flowering has no benefit and even before flowering has limited effect as the plant regrows in the following season. In all cases ensure that the cut through the stem is made below ground level to ensure damage to the rootstock and to prevent regrowth from the base. The whole plant can be removed by digging. It has been suggested but not proven that large infestations may be controlled by deep cultivation ploughing). This however, is generally impractical on river banks.

Chemical Control

Glycophosphate is the only herbicide known to control Giant Hogweed that is approved for use in or near water. Plants can be sprayed with glyphosate at a rate of 61 per ha when the plants are growing actively but still less than about 1 m high (usually April and May). Long-lance sprayers may impove accuracy of application along river banks. Glyphosate can be applied as a spot treatment to individual plants, using hand-held equipment, or as an overall spray using machine-mounted spray booms. In the latter instance, total weed control of all vegetation will occur and it may be necessary to reseed the treated area with grass and other native plants. Establishing a good sward of grasses soon after treatment of the weed will help to reduce the rate of recolonisation of the area by seeds of Giant Hogweed. Note a licence from SEPA is required before spraying near water.

Biological Control

None Known

Important Note: Giant Hogweed is an annual plant and therefore the key objective for its control is to exhaust the plants seed bank. This is done by repeatedly spraying or removing adults before they set seed.  Seed bank longevity is about seven years (can be up to 15 years) and control programmes should be undertaken for the whole of this period followed by a 5 year monitoring programme.  I

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