Bug could halt spread of superweed

Last Modified: 13 Oct 2008
Source: PA News

Scientists tackling the thorny problem of a foreign superweed hope a humble insect could halt its rampage across the UK's gardens.

The sap-sucking psyllid is the natural enemy of the invading Japanese knotweed, which has spread rapidly across towns and countryside. If the tiny insect was introduced here, it would be the first time the process of biocontrol has been used to control a plant species in Europe.

Little did the Victorians know that when they introduced Japanese knotweed as an expensive ornamental plant, it would prove the bane of horticulturists more than a century later. With no natural enemies in the UK and an ability to grow up to three metres in as many months, the weed has flourished unhindered, even affecting the 2012 Olympics site.

Just tiny fragments of the plant can form new shrubs, tearing through tarmac, so the uprooted weeds must be classed as controlled waste.

But scientists at CABI, a not-for-profit environmental research organisation, hope they have found a sustainable solution - which depends on introducing another species alien to these shores.

They identified more than 200 of the weed's natural enemies and rejected all but two which were highly-specific to the plant: the Mycosphaerella leafspot fungus, which devastates knotweed in its native Japan, and the tiny 2mm-long psyllid Aphalara itadori, which drinks its sap.

Neither are found in the UK, but scientists believe that if introduced they would bring down Japanese knotweed numbers and would not be able to feed on other plants.

Once out in the wild, the new species would sustain itself, so long-term control would be "effectively free" in comparison to the £1.56 billion bill a Defra working group put on controlling the weed's spread using traditional methods, mainly chemicals.

Dr Dick Shaw, who led CABI's research, said: "In the case of Japanese knotweed doing nothing is not an option, so we are applying a century-old technique to a new target and are very hopeful of an effective and sustainable outcome.

"Though it is more famous for its concrete-cracking ability, Japanese knotweed's impacts on our natural habitats are severe, crowding out native plants and seriously reducing opportunities for our native wildlife."

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