crop protection
Box tree moth: How to deal with the voracious caterpillars
The caterpillars of the box tree moth like to eat box trees
© Alby DeTweede / Getty Images
Once infested, they literally suck the life out of box trees: the caterpillars of the box tree moth are a nightmare for (hobby) gardeners. If they are discovered too late, the plants can usually no longer be saved.
As is so often the case, the pests are not a whim of nature, but were brought in by humans: “They probably came to us on a container ship because tree nurseries were keen on cheap box trees from Asia,” he explains Nature Conservation Union Germany registered association the background of the spread in European regions. The box tree moth is actually native to Japan and China. It was first sighted on the southern Upper Rhine in 2007, since then the small butterfly has been spreading and now also lives in the Netherlands, Switzerland, Austria, France and Great Britain. However, it is not the moth that causes so much damage to the plants – it is the caterpillars.
Box tree moth caterpillars: How to recognize the infestation
In contrast to the caterpillars, the box tree moth is usually not found on box trees, but on the underside of the leaves of other plants. However, the females prefer box trees that are not yet infested to lay their eggs, so that from March until late summer (up to four) new box tree moth generations appear again and again. The caterpillars hatch after just three days: they can grow up to five centimeters long, are yellow-green to dark green and black in color, have black dots and white bristles. Due to their preference for older leaves, they begin their feeding sprees inside the plant – and work their way outwards. As a result, the incipient defoliation of the boxwood usually remains undetected. A watchful eye is therefore important to detect the infestation.
In order to find out whether the box tree moth caterpillars are attacking your plants, you should look out for the following indications of an infestation:
- Initially, the larvae attack the top of the boxwood leaves by scraping off the top layer. As a result, the leaves get light spots, which, however, do not immediately catch the eye. In addition, there are first webs inside the plant, i.e. thin white threads in which the larvae and their residues (i.e. crumbs of droppings) can be found.
- With increasing age and growth, the caterpillar eats through entire leaves and does not stop at the branches, more precisely the bark of the shoots. The further the pests reach the outside of the plant, the better they recognize the defoliation as well as the caterpillars themselves – and their white webs, which are spreading more and more.
- At the latest when the first shoots dry up and die, the infestation is already visible from afar: the yellow leaves, the defoliation, the webs and the caterpillars leave no doubt that the box tree moth has struck. However, the good news is: “Even badly eroded box trees can recover and sprout again”, the Naturschutzbund Deutschland eV is convinced.
This is how you fight the caterpillars of the box tree moth
Two to four generations of box tree moth caterpillars can invade your garden each year, so stay alert from spring through late summer—even if you think you’ve got rid of all the pests in your box trees. Some of the most effective ways to combat caterpillars include the following tips:
- Pheromone traps for infestation control
One soaked in sex attractants pheromone trap attracts the males of the box tree moth so that they end up in the prepared container from which they can no longer free themselves. The trap primarily serves as an early warning system to find out if and when the pests will take hold in your garden. As soon as the first moths are in there, you should start combating them effectively – this is the only way to stop the spread and reproduction of the small butterflies in good time. - Biological pesticides
Most crop protection products contain the natural active ingredient Bacillus thuringiensis or neem oil They are harmless to other insects such as bees or beneficial insects, but kill the caterpillars of the box tree moth. Normally the plants should be sprayed with it for the first time in April (when the pests are still active inside the boxwood) and a second time in mid-July to increase the success. You should use a pressure sprayer take help. - Use natural enemies
According to the Naturschutzbund Deutschland eV, the caterpillars of the box tree moth initially had no natural predators. The reason for this is said to lie in the poisonous toxins of the plant, which they absorb when they eat – and thus also become poisonous. In the meantime, however, it is increasingly being observed that certain bird species such as house sparrows, great tits, sparrows and chaffinches attack the caterpillars. Therefore, you can attract natural predators by using a bird bath set up and one feeding place hang for birds. - Pick up caterpillars by hand
If a box tree is already infested with caterpillars, you must act quickly. Instead of driving the animals away with a pesticide, you can easily collect them by hand. While this takes time and patience as the caterpillars are quite quick and will hide inside the plant if they sense danger, it is still effective. You can also use one for support leaf blower or use a strong jet of water after you have first placed a plastic sheet under the boxwood to catch the falling caterpillars. Prune box trees
If none of the tricks mentioned have worked and your box trees are in danger of dying, there is only one thing left to do: you have to cut back the plants so that they can sprout again. Then burn the clippings or enclose them in a rubbish bag so that the box tree moth cannot spread further. You must then avoid infesting your plants again, as they would not survive a second attack.
This is how you prevent an infestation of the box tree moth
Last but not least, you can of course also take preventive measures so that the box tree moth – or more precisely its caterpillars – does not infest your plants. These include the following:
- If you want to grow a new box tree, look out for a possible infestation when you buy it from the plant trade – typical indicators include white webs and brown heaps of excrement.
- put algae lime preventive: The powder is intended to strengthen plants that are susceptible to pests and diseases, such as boxwood, to make them more resistant to attackers such as caterpillars. In addition, algae lime supports the regeneration of the plants.
- Make the above pheromone traps to recognize a borer infestation in good time and to take action against it – even before the caterpillars spread to your box trees.
- Check your box trees regularly, as the small butterflies appear in up to four generations per year and can therefore always return, even if you have just driven out a generation.
- Even if the box tree moth is only active between March and October, you should keep an eye on your plants throughout the winter – as the last generation often overwinters and only hatches in the following spring.
Sources: Nabu buchsbaumzuensler.net
You might also be interested in:
This article contains so-called affiliate links. There is more information here.