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The potential agents

The sap-sucking psyllid Aphalara itadori

Aphalara itadori pysillid

On 9 March 2010 approval was granted by Defra to release the psyllid and the release and monitoring programme is underway.

The psyllid Aphalara itadori is a true knotweed specialist that sucks the sap from the plant. It is about 2mm in length and capable of causing significant damage to the target weed.

It is the juvenile nymphs that cause the most damage to the plant and so where the adult psyllids choose to lay their eggs is highly important. In order to find out where the psyllid lays its eggs and whether any damage results, extensive tests were carried out on over 90 species of plants. In total, the location of more than 145,000 eggs were recorded. Only 0.6% of these were laid on non-target species or varieties and not one of those eggs was able to develop successfully to adulthood.

These findings were supported by further studies in which nymphs were physically transferred onto non-target plants and again, no adults developed. Research also shows that adult psyllids simply cannot survive even on the most closely related species to Japanese knotweed in Britain.

Based on this research, following an intentional release in Great Britain, the A. itadori psyllid should pose no threat to anything other than Japanese knotweed and the damaging hybrid variety – bohemian knotweed (Fallopia x bohemica). The rate and nature of its reproduction should mean establishment and multiplication would be successful. Furthermore, it should also be possible to integrate the psyllid control programme with current management regimes which would improve control efficacy at sites where traditional control remains necessary. 

The leafspot - Mycosphaerella polygoni-cuspidati


During the original survey, work a leafspot fungus (Mycosphaerella sp.) was observed, with damage on knotweed very commonly seen all over Japan. Its potential as a biocontrol agent was assessed alongside a rust fungus (Puccinia sp.).

The rust was rejected after failing the rigorous safety testing procedure, but the leafspot showed promising impact and safety. However, the decision was made to focus research efforts on the psyllid, on which more progress had been made.Thanks to Defra funding, the research on the leafspot has resumed and we aim to finish the safety testing of this potential agent shortly.

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