The box tree moth caterpillar was not found in the Netherlands until a couple of years ago, but the greedy insect has since spread throughout the southern half of the country. According to entomologist Rob van Tol of Wageningen Plant Research, the destructive little caterpillar is here to stay.
Is there a future for the box tree in the Netherlands?
‘Box was always a very easy shrub that would always grow. That is a thing of the past now, because this moth is not going to go away. If you catch it early enough, the caterpillar can be controlled easily. It’s mainly a question of keeping a good look out, because it is not easy to spot an infestation in the early stages. If you see that part of the hedge is growing well and part of it isn’t, it is worth taking a closer look. And it is always a good idea to push aside a few branches now and then and inspect the inside for stripped, nibbled branches.
Professional gardeners can combat an early infestation with the caterpillars well using a biological pesticide based on the Bacillus thuringiensis bacterium. Others can use natural pyrethroids. But use them with care because they kill other insects too.
Where have these moths come from all of a sudden?
‘The box tree moth comes from Asia originally but it has been found in southern European countries for a long time. It was only a question of time before it turned up in the Netherlands. The insects might have hitched a lift with holidaymakers, or have been blown here by the wind. New pests like these often come in on infected plants from abroad, but we have a lot of box nurseries in the Netherlands and import very little box. Exports are much bigger.’
Can those nurseries shut up shop or can WUR save the day?
‘To be honest, I don’t think the moth is a problem for them. Box is vulnerable to the mealybug as well, and growers are already spraying against that. The insecticide they use deals with the box tree moth as well. There is hardly any research funding because the tree nursery sector is so fragmented. Someone growing standard trees in the Betuwe doesn’t want to contribute to research for a rose grower in Brabant, and vice versa. So we are not doing much in this sector anymore.’ SvG