Controlling Japanese knotweed in Great Britain

Overview

Results

The team

Related information

So what's the problem?

Japanese knotweed is one of the most damaging invasive weeds in the UK, Europe and North America. Growing up to a metre a month, it can push through tarmac and concrete. Introduced from Asia to Europe in the mid-nineteenth century as a desirable ornamental plant, it soon fell from grace. It is now illegal to cause it to grow in the wild and it recently threatened the 2012 Olympic site.

The cost of control in the UK, if attempted, is estimated at over £1.5 billion. But current control methods rely mainly on chemicals and have been deemed unsustainable, so a longer term solution is required.

What is this project doing?

The ultimate aim of this project is to turn the weed from a destructive and expensive environmental burden, into a manageable plant which poses less of a threat to biodiversity. Since 2003, CABI has been working to stop the spread of Japanese knotweed thanks to funding from a consortium of sponsors.

The plant has significant advantages over its new neighbours as it has lost the specialist natural enemies that keep it in check in its native Japan. Having undertaken preliminary studies and literature reviews, our scientists embarked on survey trips to Japan. Along with help from Japanese scientists, we studied the plant in its native range. Potential agents were selected and brought back to our quarantine labs in the UK for further study.

Results so far

Over 200 species of insects and pathogens were recorded from knotweed in Japan and all but two were rejected under internationally-accepted stringent safety testing regimes. The two agents identified as potential controls are a Mycosphaerella leafspot fungus and the sap-sucking psyllid, Aphalara itadori. So far they are proving to be highly specific to Japanese knotweed and appear to pose no threat to important native species or crops.

With the research stage of the project now complete on the psyllid, we are now moving towards its release. Although common practice in countries such as the US and Australia, no European country has ever purposely released an agent to control an alien invasive weed to date, so since this is a pioneering project, CABI has worked closely with the relevant regulatory authorities to ensure that the most appropriate precedent is set for this and future releases.

The government's Minister for Wildlife has now given approval for a license to be issued, and we are looking to release the psyllids on two or three closely monitored sites in Spring/ Summer 2010.

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