Untangling a knotty problem
ADefra working group estimated that the cost to control it across the UK using traditional methods would be £1.56B. This is unsustainable, economically and environmentally, so CABI scientists have been researching nonchemical ways to combat this weed.
Japanese knotweed can grow up to three metres in as many months and has no natural enemies in the UK. It thrives on disturbance and has been spread by natural means, such as along waterways; and by human activity such as fly-tipping. {mosimage}
Japanese knotweed spreads very rapidly and has colonised almost all regions of the UK. It is equally happy in towns and the countryside and is a big problem in parts of Cornwall and Wales.
Due to its sheer strength, Japanese knotweed can grow through tarmac and has been known to cause serious damage to buildings, paving, drainage and archaeological sites. It even impacts on the 2012 Olympics site and can add more than 10 per cent to the total development costs of a site.
"Japanese knotweed not only causes damage to man-made structures but it also harms our native environment," said Dr Dick Shaw, Principal Investigator at CABI who has been leading research into Japanese knotweed. "Though it is more famous for its 'concrete-cracking' ability its impacts on our natural habitats are severe, crowding out native plants and seriously reducing opportunities for our native wildlife.
"In countries like the USA, Canada, Australia and New Zealand, research into natural control is the first port of call when a new pest species is identified as an apparently unmanageable problem. This has not previously been the case in the UK or the EU," said Dr Shaw.
Redressing the imbalance
The UK is leading the way in Europe in strategic invasive species management, thanks to Defra's non-native species policies, and also in researching alternative weed control measures which can be integrated with traditional methods. Since 2000 CABI has been working to stop the spread of Japanese knotweed with funding from a consortium of sponsors. They are British Waterways, Cornwall County Council, Defra, the Environment Agency, Network Rail, South West Regional Development Agency and the Welsh Assembly Government.
Natural enemies have the potential to suppress a weed's population in an environmentally sound and economical way, and once they have established and spread, their benefits are effectively free. "Almost all of the non-native invasive species introduced to the UK have arrived without the suite of natural enemies which keep them in check in their native range,"
said Dr Shaw. "What scientists call classical biological control aims at redressing this imbalance by re-associating
the plant with one or more of its coevolved natural enemies, but only after extensive safety testing under quarantine conditions, and following strict international protocols."
Successful biological control will not eradicate a species but it should bring the population to a more acceptable level, where it will become more susceptible to traditional control methods.
CABI's Japanese knotweed research project has involved the collection, identification and selection of natural enemies with potential as control agents. Over 200 species of insects and pathogens have been recorded and the most promising were tested against 79 related plant species to determine host specificity. All but two were rejected under internationally-accepted stringent testing regimes, carried out in CABI's Defra-licensed quarantine facility.
The two agents identified as potential agents for release in the UK are a Mycosphaerella leafspot fungus and a sapsuckingpsyllid, Aphalara itadori. So far they are proving to be highly specific to Japanese knotweed and pose no direct threat to important native species or crops.
Due to the difficulties of the fungus' complicated life-cycle, work on the psyllid is ahead of that on the leafspot and it is this agent that is further along the thorough expert review process. "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," said Dr Shaw.
"Of course our priority is safety and that is why we have spent the last five years safety testing the agents so that we do not have a repeat of the infamous cane toad debacle which went ahead against the recommendations of scientists at the time."
