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Knotweed Control Project

Himalayan Knotweed

Japanese knotweed is one of Britain’s most invasive weeds and is posing a real threat to some of the native flora and fauna of Exmoor. Both Japanese knotweed and its cousin, Himalayan knotweed can be seen along many watercourses on Exmoor, such as the Lyn and the Heddon and also along hedgebanks and roadside verges. The dense tall thickets have a major impact on nature conservation, archaeology, access, flood defence and the economic value of the land it contaminates.

The Exmoor Knotweed Control Project is collaboration between the Environment Agency, Natural England, National Trust and Exmoor National Park Authority.

The overall aim is to control knotweed (Japanese, Himalayan and giant knotweed and associated hybrid species) within the National Park and its associated river catchments.

Within the project area, the presence of these plants is mapped to record exactly where it is growing and how much there is at each site. Currently the most effective method of control is repeated spraying with herbicides over a number of years, which gradually reduces the vigour of the plant.

With funding from the project partners, a qualified contractor is employed to carry out a programme of herbicide spraying.  This is carried out in early autumn, when the herbicide is thought to have the most impact on the plant. New sites and larger stands may also be sprayed in early summer as well, to stunt the growth before the autumn spraying. Many sites have now greatly reduced in size and vigour but are still treated every year to prevent regrowth or spread.

In total The Project has recorded over 1100 sites across Exmoor National Park which cover the size of approximately 6 Wembley football pitches. Thanks to the co-operation of landowners and land managers, the project has been very successful to date, with many sites now showing no signs of growing knotweed or just a few small shoots.  However there is a need to continue our treatment programme for several more years.

In order to keep these plants under control, we need your help. If you spot Japanese or Himalayan knotweed or would like to speak to someone about the project please contact one of the people below. 

If you would like help in controlling knotweed on your land, then please fill in the Knotweed Consent form.


If you have any questions about knotweed on Exmoor then please email us on

knotweed@exmoor-nationalpark.gov.uk 

or contact one of team below 

Ali Hawkins, Conservation Officer (Wildlife)  - 01398 322282

Heather Harley, Conservation Officer (Farming and Land Management) -  01398 322277

Carol Carder, Corporate Support Officer - 01398 322229

Thank you for your help!


For more information:

Knotweed ID Guide

Japanese Knotweed Information, Devon County Council