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Tiny weapon unleashed on monster weed

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Japanese knotweed: insect predator to be released

11 March 2010

Nymphs of the psyllid. Image: Dr Dick Shaw-CABI

The government has given the go-ahead for the trial release of a tiny sap-sucking insect from Japan which feeds on the notoriously invasive Japanese knotweed and could help halt its march across the country.

The psyllid, Aphalara itadori, is a jumping insect just a couple of millimetres long. It feeds on the sap of knotweed plants, stunting growth and so limiting its spread. They will be released in a handful of isolated sites in England to begin with, with insecticide treatments on standby to control them if there are any adverse effects.

'This project is not only ground-breaking, it offers real hope that we can redress the balance,' said Wildlife Minister Huw Irranca-Davies.

It's the first time a non-native insect has been deliberately released as a biological control in Europe and follows10 years of research and months of public consultation. However it remains controversial, with conventional knotweed control companies and some wildlife groups expressing concern that the insect may itself become a problem.

'Just like knotweed, the aphid is an alien species and has no known predators in the UK,' says Mike Clough, managing director of Japanese Knotweed Solutions.

Japanese knotweed was introduced to the UK by Victorian plant hunters but rapidly became an invasive weed so vigorous that its roots can penetrate concrete. It's estimated knotweed currently costs the economy over £150 million a year to control, largely through the use of chemical herbicides.

Part of the reason for its rampant growth is that it has no diseases or pests in this country, unlike in Japan where the plant is common but does not cause a problem. Scientists at agricultural research centre CABI went to Japan to collect dozens of natural pests and pathogens specific to knotweed and brought them back to the UK for exhaustive testing.

Most were rejected because they attacked other, more welcome members of the Polygonaceae family such as bistort (Persicaria bistorta) as well as Japanese knotweed; the psyllid was the only one found to be species-specific. Lead researcher on the project Dr Dick Shaw remains confident that everything has been done to make sure the psyllid does only what it was released to do.

'This is a great opportunity for the UK to benefit from a technique commonly used outside Europe,' he said. ''We have every reason to believe that this knotweed specialist can help limite the impacts of this harmful invasive weed safely and sustainably.'

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