Invasive Plants: Giant Hog Weed

Giant Hogweed (Heracleum Mantegazzianum)


The sap of giant hogweed contains a toxic chemical which

sensitises the skin and leads to severe blistering when exposed to sunlight.


The Problem for Anglers

  • 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

This is a plant which not only causes problems for other vegetation resulting in erosion and siltation, but also kills off invertebrates. Additionally it can be dangerous to humans through its sap.

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.

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.


What can we do?

Some clubs have had success by digging out or by chopping the roots below the surface.

At this time the club is not proposing any action, this posting is for awareness of the risks posed.

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