A tiny mottled brown insect from Japan is soon to be released in parts of the UK to stem the spread of Japanese Knotweed, a non-native plant that is growing wildly out of control all over the country.

First introduced in Victorian times as an exotic garden plant, the rampant growth of Japanese Knotweed in the wild now costs 150 million pounds each year to remove and control.

The plant can grow up to one metre a month. Its tough roots and stems can break through tarmac and concrete causing havoc when it appears near roads and buildings.

As well as the economic cost, there is a cost to the environment as the plant takes over and destroys native habitats and the plants and animal in those areas.

The reason that the plant has caused such a devastating impact on the UK environment is that it has no natural enemies here so it has been able to rampage through natural habitats.

In Japan the plant does not cause a problem because it is kept in check by over 200 plant-eating insects, and disease-causing fungi. 

CABI, a global organisation offering scientific advice and information on agriculture and the environment, has spent years researching these natural predators. They have tested them on 90 native UK plants, including key crop species, in order to find one that will effectively control the Japanese Knotweed without damaging other plants growing around it.

The insect, called a psyllid, is just over 2mm long. The nymph in particular feeds on sap from the Knotweed causing stunted and deformed growth.

This is the first time a natural pest control solution has been used in Europe. Defra has approved the first releases this spring at two or three sites, which will be closely monitored. If successful, more insects will be released in other locations but it is likely to take 5–10 years to control the weed to a manageable level.