Trust working to eradicate invasive knotweed

Cornwall Wildlife Trust has begun work to eradicate Japanese Knotweed which can be bad news for wildlife and people alike from the Drift Reservoir Catchment in west Penwith. South West Water is funding the Trust to treat Japanese Knotweed over the next five years to try and completely remove this problem plant from the whole Drift Drinking Water Catchment.

Japanese Knotweed is a fast growing, invasive plant which spreads rapidly forming large stands that can reach over seven feet in height, easily shading out and taking over from the wildflowers and plants that occur naturally in our countryside. This leads to a loss of suitable habitat for wildlife. Japanese knotweed is also an issue on river and stream banks where it causes soil erosion. This problem plant can even cause structural damage to roads and property.

Japanese Knotweed doesn’t occur naturally in the UK and is thought to have been bought over as an ornamental plant in the 19th Century by the Victorians. It has large bamboo-like green stems that are often speckled red, lime green heart-shaped leaves and clusters of cream flowers in the summer.

Liz Cox, Upstream Thinking Ecologist for Cornwall Wildlife Trust says,

“I am delighted that South West Water is funding Cornwall Wildlife Trust to control Japanese Knotweed in the Drift catchment over the next 5 years. The Trust is in a great position to tackle Knotweed in the catchment, as we already work closely with many farmers and landowners locally through our Upstream Thinking work which is also funded by South West Water. Controlling Japanese Knotweed fits well with Upstream Thinking’s aims to enhance water quality and wildlife habitats in the area.”

Liz Cox continues,

“Japanese Knotweed is a real threat to some of the fantastic wildlife habitats in the Drift area, where it is growing in areas of woodland, wetland and heathland. As well as treating Japanese Knotweed in these valuable habitats we are also tackling stands in farmyards, gardens and on stream edges to prevent the knotweed spreading downstream and ultimately to Drift reservoir itself.”

Japanese Knotweed

Liz Cox

Japanese knotweed spreads through an underground, rhizome (or root), so cutting it or digging it up should be avoided as it can cause it to spread, even from the smallest fragment. Japanese Knotweed can take up to 5 years to control and the Trust has sought advice on the best way to do this from Cormac who have a huge amount of experience controlling Japanese Knotweed across the County for Cornwall Council.

Tim Bird Natural Environment Adviser for CORMAC says,

‘This project is extremely positive and provides a proactive approach to dealing with this invasive non-native plant. I am delighted to be working with and advising Cornwall Wildlife Trust on best practice and national standards of treating Japanese Knotweed and am confident this project will succeed in controlling the Knotweed within the project area. CORMAC are well placed to provide support and advice on Japanese knotweed control, as we are members of INNSA (Invasive Non-Native Specialist Association) who have recently produced a Code of Practice which has been implicit in providing technical advice to the Trust.

Tim Bird continues,

“There is a lot of uncertainty on how to manage Japanese Knotweed and I have seen people cutting stems which is not an ideal approach. Cutting actively growing knotweed stems will invigorate plant growth and the live stems, root crown or rhizomes are extremely active and can all regrow into new plants. The plant material is also classed as `controlled waste’ and cannot be recycled as compost or placed in any general waste, therefore needs to be sent to a licenced waste facility.”

For more information on how to control Japanese Knotweed visit For more about Upstream Thinking visit