Exmoor Knotweed Control Programme

Knotweed Control Programme

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 Programme has been running for 15 years and now falls under the ENNIS Project. The overall aim of this programme is to control knotweed (Japanese, Himalayan and giant knotweed and associated hybrid species) within the National Park and its associated river catchments.

The programme works closely with Exmoor's communities to map and record the locations and vigor of knotweed infestations within the National Park. Normally it is the landowners responsibility to control invasive species but our  programme is currently able to support landowners by offering to treat the knotweed on their land. Currently the most effective method of control is repeated spraying with herbicides over a number of years, which gradually reduces the vigor of the plant.

knotweed spraying

A qualified contractor is commissioned to carry out a programme of herbicide spraying in early autumn (September to November) when the knotweed plants absorb the greatest amount of herbicide. This is considered the most effective time of year because the herbicide causes the greatest amount of damage to the plant.

In total the programme has recorded over 1180 sites across Exmoor National Park. Thanks to the co-operation of landowners and land managers, many sites have greatly reduced in size and vigour sprouting single shoots or not showing any above ground growth at all. Continued annual treatment and monitoring is vital to controlling the spread of knotweed because of its rapid growth rate and the fact that its rhizomes (roots) can stay dormant in the ground for approximately nine 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, or if you have any questions about knotweed on Exmoor then please contact us by:  


Phone: 01398 322259

Holly Moser and Charlotte Thomas (ENNIS Project Officers)

If you are already part of our Knotweed Control Programme and you would like to give consent for next years treatment please complete our online Knotweed Consent Form.

For more information:

Knotweed ID Guide

Japanese Knotweed Information, Devon County Council