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Last Updated: Thursday, 12 June, 2003, 10:05 GMT 11:05 UK
Foreign recruits join weed war
UK scientists are hoping to import bugs from abroad to help control the rampant spread of a weed that is costing more than a billion pounds to control.

Path obscured
Whole paths are swallowed up by the weed
Japanese knotweed (Fallopia japonica) was first introduced to Britain by the Victorians as an ornamental plant - and was actually awarded a gold medal at a prestigious flower show.

However, this was revoked within a few years when botanists realised exactly what an unwelcome guest it was.

Now, local authorities are desperate to find an effective way to eradicate the plant as it overruns riverbanks, railway embankments, gardens and hedgerows, threatening the survival of other, important plant species.

Huge sums are being spent in the UK controlling the weed. A recent Defra (Department for Environment, Food and Rural Affairs) review of non-native species policy stated that a conservative estimate for the costs involved would be 1.56bn.

Part of the problem with the knotweed is its resilience - and lack of natural enemies in the UK.

Beetle battle

It is easy to chop back the plant at the stem, but the plant is equally active beneath the surface.

It has an underground rhizome which can spread up to seven metres from the original stem.

Knotweed rhizosomes, CABI
A load of trouble: Knotweed rhizomes
Even if this is ploughed up, a new plant can grow from discarded tissue that is the size of a fingernail.

Pesticides will kill the plant, but this can take years of applications - and experts are concerned about the toll heavy herbicide use will have on other plants and animals.

Now, a research team from the UK is hoping to gain the upper hand against knotweed by introducing the organisms which keep it under control in its native Japan.

It is possible that beetles which eat the foliage and bore into the stems of knotweed plants, or perhaps a rust fungus which attacks the plant, could be brought into the fray.

Concrete breaker

Dick Shaw, a "biocontrol scientist" at CABI Bioscience who is heading the 500,000 project, says that it could become the first "natural control" project involving a weed in Europe.

He said: "Natural control has a very good safety record. Whatever we want to use will be extensively tested in quarantine to make sure it does no harm.

Riverbank and knotweed, CABI
Don't just flail or mow it down - you'll spread it
Don't put it in compost
Don't dump contaminated soil - you're breaking the law
Do work quickly - deal with it as soon as you can
Do repeatedly rip it up and cut it down - eventually it will die
"Japanese knotweed is a very tough plant, and without any natural enemies it has a clear advantage.

"When we showed pictures of knotweed in Devon and Cornwall to people in Japan, they were amazed at what it could do.

"We are not expecting natural control to be a silver bullet, but we are hoping that it will stop invading, and perhaps begin to contract." Colin Hawke, who jointly chairs the Knotweed Forum at Cornwall County Council, is all too well aware of the destructive potential of knotweed.

He told BBC News Online: "A particular concern is its effects on biodiversity - it grows in large 'stands' and smothers native varieties and important habitats.

"It can even cause structural damage to concrete and tarmac, and of course obscures road signs."

'Plant clone'

The county spends an estimated 250,000 a year on anti-knotweed action at present, and other areas such as Devon and South Wales are also fighting the advance of the weed.

"We just hope we can find an organism which can safely reduce the spread."

Scientists believe that any organism that can attack knotweed will be able to tackle the plant wherever it is found in the UK.

Japanese knotweed is essentially just one plant - every stem has grown up from a fragment of the original root imported into the UK, and as such every plant shares the same genetic identity.

The project has been funded by a wide variety of organisations, including Cornwall County Council, the South West of England Regional Development Agency, the Welsh Development Agency, British Waterways, the Environment Agency, Network Rail and Defra.

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22 Oct 99  |  Science/Nature

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