Plant-eating insect could finally kill off Japanese knotweed

As even Chelsea Flower Show falls victim...

JAPANESE knotweed’s stranglehold on the British countryside could soon be coming to an end.

Experts at the Chelsea Flower Show yesterday revealed that they believe they can cut the invasive plant down to size with two pieces of special ‘weaponry’ – an insect and a fungus.

In a sign of how pervasive Japanese knotweed is, yesterday it also emerged that the weed is even growing at the West London show site.

Scientists from the Centre for Agriculture and Bioscience International are masterminding the two-pronged fightback against the invader. They say the insect and the fungus, both native to Japan, attack and cause disease in the weed, which was first introduced here in the 19th century as an ornamental plant.

Knotweed has rampaged across Britain’s countryside, riverbanks and waste ground. However, it can also grow through concrete and undermine buildings. Its cost to the British economy is an estimated £165million a year, so a method of controlling the weed is urgently needed.

The tiny insect that could be the answer to the problem is called a psyllid – and it has already been released in the wild across the UK to test its effectiveness.

It only attacks knotweed and is harmless to native plants. CABI has also patented a spray which causes ‘heavy damage’ to knotweed but has no effect on other species.

The spray contains a fungus which will greatly weaken the plant – but does not attack native species.

Dick Shaw, CABI’s UK director, said Japanese knotweed’s infestation of the UK had come about because it has no natural enemies here. He said: ‘We have two irons in the fire. We’ve found a fungus which attacks the knotweed we are considering using as a mycoherbicide. This is basically a fungus-based herbicide. The patent is in. The next step will be to develop the product. That’s a long term thing and it could take five to ten years.’

The psyllids, meanwhile, suck the sap of the plant. Extensive tests on UK plant species show that the insect is highly plant specific – it only likes to attack knotweed.

Dr Shaw said the psyllid was released across the UK under licence in 2010. ‘We are doing an awful lot of safety work to make sure it’s not been misbehaving,’ he said. ‘We now know the psyllid is safe.’ He compared the insect to an aphid preying on roses. ‘If you have got aphids on your roses, your roses don’t do very well.’ While the psyllid will not destroy knotweed, it is hoped the bug will greatly weaken it, making it easier to kill and more susceptible to attack.

Dr Shaw said: ‘We found 186 insects and 40 fungi that attack knotweed. There are an awful lot of things feeding on it in Japan.

‘Our job was to find something that was safe to release in Britain.’

Current methods of killing knotweed involve repeated applications of a herbicide. A spokesman for Chelsea organisers, the Royal Horticultural Society, confirmed it was aware Japanese knotweed was infesting parts of the grounds – but eradication methods so far had not worked.