The non-native species policy review working group estimated that to control the invasive alien plant, the Government needs to spend more than £2.6bn. Clough said although the introduction of the aphid would "appear [to be] a cheap and effective solution to halt the growth of the plant" and is not likely to cause the same environmental damage as the cane toad that was introduced to Australia, "careful consideration needs to be made".
He cited the Government's own Pest Risk Assessment: "It is not certain that Aphalara itadori could be contained or eradicated once it has spread beyond the limited release area."
Some 87 species from the UK's total biodiversity range have been tested by CABI against the aphid but Clough said: "There are no guarantees that the aphid won't cross-breed or even become attracted to other plants as its natural home declines."
He added: "Having to wait for an aphid to eat the foliage simply would not provide the solutions needed for the beleaguered construction industry and, most importantly, Aphalara itadori does not actually kill knotweed but simply helps manage its growth — thus it is not tackling the problem."
He said current herbicide and excavation eradication methods remain expensive, while including knotweed in the Weeds Act would be unpopular with the Environment Agency, Network Rail, the Highways Agency and local authorities.
Clough said the Government should legislate against the spread of Japanese knotweed and support landowners with the problem. He called for a co-operative approach between the public and private sectors to use all available resources to stem the spread of the weed.