Beetles called in to beat knotweed menace

Japanese knotweed, a vigorous, fast-growing "super-weed" that is invading thousands of miles of British riverbanks and displacing natural wetland vegetation, may finally have met its match: Japanese beetles, caterpillars and "rust" fungi that together control the weed in its native habitat.

Japanese knotweed, a vigorous, fast-growing "super-weed" that is invading thousands of miles of British riverbanks and displacing natural wetland vegetation, may finally have met its match: Japanese beetles, caterpillars and "rust" fungi that together control the weed in its native habitat.

Brought to Britain in the 19th century by plant collectors who admired its tall bamboo-like stems, fluffy white flowers and red autumnal foliage, the Japanese knotweed quickly spread beyond ornamental shrubberies and established itself in the wild. Now it is endemic throughout England and Wales, especially in high rainfall western areas, and has proven its ability to survive the strongest of herbicides.

Vital to the knotweed's success is its massive, powerful root system, which has been known to reach a depth of 15ft. Once a colony is established, the roots send out underground shoots, which allow the plant to colonise fresh ground all around it.

Now, in an attempt to control the knotweed, scientists at the Environment Agency and CABI Biosciences are investigating the idea of introducing the natural predators, which prevent it from being a problem in its native Japan. First in line for study are several chrysomelid beetles, which defoliate the plant, and eight different rust fungi.

"Our only hope is to fight nature with nature," said Trevor Renals, a biologist at the agency's office in Bodmin, Cornwall. "Bio-control could save millions of pounds being spent now in short-term measures, and we hope it will prove far more effective."

The idea will be put forward at a meeting next month that is being organised by CABI, an inter-governmental biological research organisation. The meeting will consider whether to allocate £416,000 to finance field work and subsequent research.

The final decision about whether to use biological controls will lie with the Department of the Environment.