Knotweed breaking through a paving slab
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Swansea University scientists trial knotweed killers

28 August 2014 Last updated at 20:41 BST

Swansea University scientists are conducting the largest field trial in Europe to find new ways of killing Japanese knotweed.

The plant is one of the most damaging species in the UK and costs £8m a year to bring it under control in Wales.

Carwyn Jones has been finding out more.