Invasive non-native plant and animal species are costing the British economy around £1.7bn every year, according to a new study from CABI, and Japanese knotweed accounts for £165m of that.
The Economic Cost of Invasive Non-Native Species to the British Economy was carried out for DEFRA, the Scottish Government and the Welsh Assembly Government and looks at impacts across a whole range of sectors including agriculture, ecosystems and development.
Agricultural losses account for £1bn of the £1.7bn.
"Invasive non-native species have a significant impact on the British economy and damage our own wildlife," said environment minister Richard Benyon.
"The costs of controlling these species will rise unless society takes steps to prevent them taking hold and spreading."
The report looks in detail at Japanese knotweed, signal crayfish and floating pennywort and includes five case studies.
It says knotweed displaces native flora and causes structural damage.
Almost 3% of the planning applications to Swansea City Council required knotweed conditions, although the figure has fallen recently thanks to increased awareness and nationally it estimates 2.66% of applications are so affected.
Costs of knotweed control on development sites are very varied, with costs of treating a five metre square patch ranging from £800-8,000/m².
A mean site cost culled from contractors was £5,800 + VAT, although anecdotal information put the figure higher and, adding the cost of delays etc., a figure of £11,600 per contract was used, yielding an annual knotweed cost on development sites for Great Britain of £150m.
CABI assumed 1.125% of households would be affected each year, each spending £15 on eradication, adding a further £448,000 to the GB bill.
More serious for householders is the loss of value on their homes (one mortgage provider is already refusing loans) and applying the 1.125% infestation figure to almost one million sales and deducting a notional 5% (£9,925) to each would suggest a cost of £111.5m a year, but CABI suggests this is only true in 1% of cases, yielding a cost of £1.16m.
A number of other costs, including costs to roads, railways, riparian habitats and local authorities all add to the £165m total.
"We all know about the serious threat to our native wildlife from invasive non-native species, and this report confirms the huge cost to businesses and individuals in Great Britain every year," said Scottish minister for environment and climate change Roseanna Cunningham.
Also looked at was floating pennywort which infests at least 150 water bodies in England and Wales where it forms dense mats.
Here the annual cost is estimated to be £25.4m.
"This report will help us to prioritise and target where actions can have the most impact, and will assist us in prioritising our resources for action in the future," said Welsh minister for environment, sustainability and housing, Jane Davidson.
