Japanese knotweed bio-control agent

Last week Defra announced Government approval for the release of a biological agent to control Japanese knotweed. Alaphara itadori is a sap sucking psyllid that feeds on Japanese knotweed in its native range in Japan.

Having submitted a detailed consultation response to Defra last year and having attended a Defra workshop to discuss the proposals, Phlorum remains sceptical of the likely success of the project. There are many reasons why the effect of the psyllid on Japanese knotweed might not be as significant as the press are currently reporting.

The research carried out so far has been with a small population of psyllids on small, immature knotweed plants in small, controlled environment chambers in the laboratory. Results from these experiments on the actual efficacy of the psyllid on knotweed are mainly anecdotal, unpublished and not peer-reviewed. There has apparently been no research on how the ecology of knotweed in the UK differs from that in its native range, which could significantly alter the relationship between Japanese knotweed and the psyllid. The lifecycle of the psyllid in the UK is also not understood. It is believed that it might overwinter on coniferous trees, but this has not been tested.

Possibly to appease knotweed contractors worried that the psyllid might put them out of business, Defra has also been keen to point out that the psyllid will make herbicide applications on Japanese knotweed more effective, but no detailed work has been undertaken to test this.

It is hoped that the questions raised above will be answered by ongoing research in the field. However, we believe that many answers could have been found with more research in the laboratory, well before the risks of releasing an alien species into the wild were accepted. It has been suggested that the release might have been brought forward due to the laboratory population of psyllids being weakened by successive generations of inbreeding. If this is so, it suggests that the risk of releasing the psyllid into the wild was accepted with unacceptable haste.

We await, with interest, the results of this new phase of the research.

Japanese knotweed hidden by snow

It’s actually often easier to survey sites for Japanese knotweed plants in the winter. This often surprises our clients who want it identified and eradicated.

In the summer you have thickets of brambles and other vegetation that can hide smaller Japanese knotweed stems. In the winter, when the shoots or leaves of most other plants in the field layer have died down, Japanese knotweed crowns can be identified by the dead, bamboo-like knotweed canes that persist – even if the old knotweed shoots are only 10-50cm tall. However, with the recent snow covering much of the UK, finding Japanese knotweed on sites where it would otherwise be relatively easy, has become very difficult… Hurry up spring!