‘That makes it sound really exciting’, laughs Jaike Bijleveld, the invasive exotics coordinator responsible for the study currently underway in Zuidas. But she agrees that combating Japanese knotweed is high on the agenda. ‘The Japanese knotweed jumping louse is actually the plant’s only natural enemy, so we hope that it feasts on this invasive weed.’
Strong and tenacious
It’s generally agreed that we could do with some help in eradicating Japanese knotweed. The plant was imported from Japan in 1850 by a botanist from Leiden. It soon turned out that it thrives in the Netherlands. Bijleveld: ‘In itself, that should not be such a problem, but it wreaks destruction as it advances.’ Knotweed can cause damage to street paving, the foundations of houses or canal walls, cables, pipes and sewers. To add insult to injury, the plant is also extremely tenacious. ‘If just a few millimetres are left over after removal, it will regrow just as strong.’
The fight against Japanese knotweed is clearly in need of reinforcements. They come in the form of Japanese knotweed jumping lice, now being released in Zuidas, behind fencing and on the knotweed. But won’t this just cause new problems? ‘This process has been studied in laboratories for years and applied in practice in the UK. Some of the smartest brains have been waging this battle for quite a while. The jumping louse can only live and reproduce on Japanese knotweed and will therefore not attach itself to animals, people or other species of plant or tree. The main question is whether the thousands of lice we have released will be able to survive in our climate.’
This study will initially last for a year. Bijleveld: ‘We are currently placing the specially-reared lice in pots between the Japanese knotweed and hanging them onto the ends of the plant in small bags. This means that, in the spring, the lice will not need to jump but will already be sitting on their primary food source, the sap in the shoots of the knotweed. In the period ahead, we will be monitoring whether the lice, currently entering hibernation, are still alive and will start feeding and reproducing in the spring.’ Will that mean that the Japanese knotweed on Piet Kranenbergpad could be a thing of the past by 2022? ‘Sadly, it won’t be happening that fast. If the study is successful, the main thing will be that the louse becomes a great ally in the battle against knotweed and keeps its growth in check. If we really want to completely remove the knotweed, we’ll need to continue to take tough measures.’
The study in Zuidas is a collaborative project involving the City of Amsterdam, Leiden University, Koppert, Stowa, Cabi and Probos. The louse is also being released on Japanese knotweed in Zeist and Lage Mierde.