Britain calls on alien parasites to take fight to Japanese knotweed

An army of jumping plant lice is to be released into Britain in the hope that they can save the countryside from the ravages of Japanese knotweed.

It is estimated that controlling the plant using ordinary methods, such as pesticide, would cost about £1.6bn, so government scientists have come up with a plan to bring in the plant's natural predators from Japan. If given the go-ahead, it would be the first time an alien species has been released into the wild to deal with a weed in the UK.

The lice, also called psyllids, lay eggs on the plant and the hatched larvae suck out the sap.

Scientists at Commonwealth Agricultural Bureaux International (Cabi) believe they will not cause any environmental damage. Other experts urged caution, saying introducing them might have unintended consequences, such as feeding on British relatives of the knotweed.

But Dick Shaw, principal investigator at Cabi, said such was the devastating effect of knotweed that it was time to act. "Japanese knotweed has been described as having the biodiversity value of concrete – it just smothers the ground in a mass," he said. "We hope the psyllid will get the plant under control."

Japanese knotweed, which was brought to Europe as an ornamental plant, grows up to 3m in height and sends out a root-like stem system that can reach the same distance below ground. Fresh stem fragments of less than a gram in weight can produce a viable plant in just six days. It can cost several pounds to completely clear the weed from a square metre of ground in the countryside, but on land for development, that can rise to £54,000 because of the need to ensure absolutely nothing is left and dispose of it responsibly.

In an attempt to see if the psyllids would stick to their usual diet, the Cabi scientists have tested the lice on nearly 100 plants and crops that grow in Britain, without finding any problems. There seems little doubt that the arrival of the insects would have a dramatic impact. When the eucalyptus psyllid was accidentally introduced in Ireland, which started commercial production of the tree in 1993, a report described its effect on the crop as "disastrous".

They proved resistant to pesticides, despite more than five applications a season, and a parasitic wasp from Australia has since been introduced in the hope they will see off the lice.

Craig Macadam of Buglife: The Invertebrate Conservation Trust, said: "Do they only eat Japanese knotweed or do they eat domestic plants? We do have native knotweeds in this country. It is a question of whether these things would feed on those, too."

Chris Rostron, of The Wildlife Trusts, added: "Invasive species such as Japanese knotweed pose a serious threat to Britain's biodiversity, particularly wetland habitats. But introducing any non-native species for biological control carries risks and must be thoroughly researched."

Attack of the clones

*While there are male and female versions of Japanese knotweed and it does reproduce sexually, all the plants in Europe are clones of the same female. The original plant would have sent out lateral stems called rhizomes from which a new plant can be created. The same clone has been found all over Britain, across Europe and even in North America. It has been estimated that the total amount of the plant in the Swansea area alone weighs 62,000 tonnes, equivalent to 40 blue whales. The plant is native to Japan, northern China, Taiwan and Korea. The Orkney Islands are the only places where it is not found in the UK. It can be found across Europe, from southern France and southern Italy to Norway.