National / Science & Health

Japanese knotweed scourge: British and Kyushu scientists identify key to tackling plant invasion

by Imogen Pullan

Kyodo

Scientists in Britain may have finally found the answer to the perennial menace of Japanese knotweed, although it has come too late for one unfortunate pensioner.

The plant, first brought into Britain by Philipp von Siebold in 1850 and once prized by landowners for its stately appearance, has since spread exponentially across the country and is estimated to cost the economy £165 million (about ¥24.9 billion) each year.

Robin Waistell, 70, from Maesteg, Wales, is all too aware of the damage knotweed can do. He has spent more than four years battling rail authorities after finding the knotweed spreading onto his property from a nearby train track had wiped £60,000 (¥9 million)off the value of his home.

Although any knotweed found and reported on railway land is put through a chemical treatment cycle, Waistell said the process has been like “bashing your head against a brick wall,” and two attempts to eradicate the invasive plant have been unsuccessful.

If he wins his case, it could lead to an explosion of similar cases submitted in the former coal mining town, which is now overrun with knotweed and Himalayan balsam, another invasive plant species found all over the country.

Waistell has been waiting for over four years for a resolution to his case, which will soon be heard by a judge following a final appeal by the rail authorities.

Earlier this year he was diagnosed with a terminal illness and is hoping to return to Spain, where he previously lived, as soon as possible. “I want to go back to die. I can’t sell it (the property) until we’ve had the decision from the courts. If I could sell this today for near market value, I would be gone tomorrow,” he said.

Waistell is one of a huge number of homeowners struggling with knotweed. Many have faced a daunting task in trying to control the plant. The invasive species has no natural predators. It often encroaches from nearby waterways and railroads and can render property nearly impossible to sell.

Rodger Burnett, the lawyer representing his case, has dealt with over 200 knotweed claims and believes the stigma of the plant is strong enough to put off most people from buying.

Help may yet be at hand thanks to work being done by scientists at the Centre for Agricultural and Biological Sciences.

Dick Shaw, country director for the U.K. office of the Centre for Agriculture and Biosciences International, spoke about their collaboration with Kyushu University to identify a natural predator of knotweed in Japan that could be released into the wild in Britain without causing its own biodiversity crisis.

CABI scientists have spent the last seven years attempting to introduce bugs known as psyllids (Aphalara itadori) into the wild but have struggled to keep enough of them alive through the winter to form self-sustaining populations. They are a specific type of jumping plant lice that feed off Japanese knotweed.

Shaw explained that although they now have a good understanding of the bug, their original stock has since grown too used to the luxury and comforts of the laboratory. CABI has now brought in new stock that he hopes will be more viable in the wild.

Although reluctant to put a deadline on the project, Shaw is cautiously optimistic.

“I’d probably start the clock from two years ago (when the new stock was first put in use) and say five to 10 years,” Shaw said.

Another solution being explored by CABI may be more helpful to the individual homeowner. The organization has recently submitted patent applications for an invention by Daisuke Kurose that could soon be sold across the counter.

Kurose initially assisted the collaboration between Kyushu University and CABI as a Ph.D. student, and is now a full-time research scientist at the latter.

The Japanese leaf-spot fungus was identified early on as a possible natural predator but was found to attack a nonnative species in Britain and had to be disqualified. Kurose, however, has found a way to create a spray using the fungus spores that does not threaten other plants, and it could be on the market in the next five years.

Unlike the psyllid bugs, t his spray could be used directly by homeowners to tackle the knotweed in their garden without damaging surrounding plants.

Currently, the recommended option is to pay for professional treatment of the plant, which can range in price from £2,500 to £30,000 (¥377,000 to ¥4.5 million) for a serious infestation.

In the meantime, frustrated homeowners can always turn it into food: Shaw has made knotweed muffins and knotweed jam, which he recommends to any lovers of rhubarb.