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Plant-Eating Predators Answer To Britain’s Alien Predators

October 13, 2008

Scientists in Britain believe a Japanese plant-eating predator may help solve the problem of a “superweed” that is now spreading across the country.

Japanese knotweed, like many other non-native, invasive plants, was first introduced to Britain for horticulture. Its ornamental leaves, 10-13 ft stems and clusters of white flowers made it attractive in gardens. However, it has since plagued the environment, and this year has been particularly bad for knotweed spread in the UK. Making matters worse is the costly and time consuming work required to remove the weed. 

However, a team of scientists has identified natural predators from its native home in Japan that may also serve to control the knotweed in Britain. Plans to use the plant-eating predators have been submitted to the British government, and are now awaiting approval.

Should the government give its blessing, it will be the first time that biocontrol, the use of a natural enemy to control another pest, will be implemented in Europe to fight a superweed.

“The weather patterns have ended up with us seeing a lot of knotweed spread in a number of areas,” James MacFarlane, vegetation adviser for Cornwall County Council, told BBC News.

In Japan, native home of the knotweed, the plant is common but does not grow out of control as in Britain.

“In 2000, we went out to Japan to see whether the plant had any natural enemies that it had lost when it came here,” Dick Shaw, who led the research, told BBC News. 

Shaw is with the not-for-profit agricultural research organization Cabi.

“We found that it had a lot: there were 186 species of plant-eating insects and about 40 species of fungi,” he said.

The team then started testing the predators to identify only those that with an appetite for Japanese knotweed, and not others.

The researchers lured them with species closely related to knotweed, less closely related species and prominent British plants such as wheat and apples. Those that pursued plants other than Japanese knotweed were then excluded, said Dr. Shaw.

Eventually, the list was pared down to only two predators: a sap-sucking psyllid insect (Aphalara itadori) and a leaf spot fungus from the genus Mycosphaerella.

“We have done some efficacy trials here in the lab and they are showing a significant impact,” Shaw told BBC News, while showing the effects of the sap-sucking psyllid on the knotweed.

While successful biocontrols can bring a target weed under control, they cannot completely eradicate them as this would mean eliminating their only food source, effectively making themselves extinct.

“The psyllids are having an effect on the plants’ height and the treated knotweeds produce tiny curled leaves rather than big light absorbing leaves, which means that less resources will get to their root system,” said Dr. Shaw.

“The nymphs are literally sucking the life out of the plant,” he added.

“Japanese knotweed first came into the UK in 1840 through Wales – but it was only about 10 to 15 years later that people started to see it as a threat,” Simon Ford, a National Trust nature conservation adviser, told BBC News.

The plants grow rapidly, with some growing as fast as four meters in just four months. And they can spread at a incredible rates, quickly obliterating nearby vegetation.

“By the time they realized this it was already far too late,” Ford said.

Japanese knotweed is highly prevalent throughout Britain today, and has caused significant damage to the plant biodiversity. It also causes issues for buildings, flood defense structures, and other hard facilities.

Experts estimate that removing all the knotweed from Britain would cost upwards of several billion pounds.  But the Cabi scientists believe natural control would provide a much simpler, elegant solution to the problem.

“In comparison to the current control methods, if it works, this will be significantly less costly,” Shaw said.

The team has submitted its proposals, which will now be reviewed by the Department for Environment, Food and Rural Affairs (DEFRA) and independent peer groups.  It will then be submitted for a public consultation.

Image Courtesy Wikipedia

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