Japanese Knotweed causes developers and property owners stress and expense in the UK and there have been many discussions about the best way to manage its growth.
Most countries are very reluctant to use biological controls as these have often caused more problems than they were originally introduced to control. If you have an hour to spare, check out the often hilarious documentary about the introduction of the Hawaiian sugar-cane toads through Australia in a botched effort to introduce them as counter pests (Cane Toads: An Unnatural History).
However, the Dutch government has made an unusual decision to issue an exemption on the ban on introducing alien species in the face of spiralling costs related to controlling Japanese Knotweed.
Preliminary tests in the Netherlands have suggested that Japanese knotweed psyllids or leaf fleas, can kill young shoots and potentially stop the plant growing by sucking up their sap. Now they just need to check whether the fleas can successfully hibernate over winter and establish themselves in the new year.
Suzanne Lommen, the entomologist coordinating the trial has said: “Complete pest control is extremely difficult and very expensive. We will have to combine various methods to get the Asian knotweed under control. We know from the Japanese knotweed psyllid that it can kill young shoots and slow down or even stop the growth of the plant by sucking up sap – nutrition – from the plant. If the psyllid can establish, reproduce and spread, and do the damage we see in the breeding trials, it can hopefully inhibit the growth and spread of Asian knotweed. Then you have a very cheap and environmentally friendly solution with many years of effect that you can combine with the more expensive methods.”
It has been concluded that the psyllids do not pose a threat to native biodiversity but there is a chance the fleas will not take to the Dutch climate – hence the anxious wait to see if they successfully survive the winter. We will watch with interest.