Le Potager d'Arthur
The 'box tree moth' plague: 5 effective ways to keep them away! (EN)
Updated: Mar 8
Have you also been bothered by the box tree moth? Then you've found the perfect article! What are those green, little caterpillars? How do I recognize them? How do I keep them away? You'll find the answers right below!
The 'Box Tree Moth'... What is it?
First of all, let's begin with the pest itself. The box tree moth is a small white and brown moth native to Asia and has been imported unintentionally about a decennium ago when there was an explosive demand for boxwoods. Tremendous amounts of boxwoods were imported from Asian countries but our little "friends", the box tree moths, secretly came with it during the shipping. That's the story of the box tree moth in a nutshell.
How can you recognize them?
If you want to see box tree moths, you'll better do it at night: moths are nocturnal, after all, so you won't see them during the day.
The moths are white with a brown border and about 4 cm big (1.5 inch). For an example, see picture at "The Box Tree Moth... What is it?"
But your boxwood don't fear the moths, no, they fear their larves! (see picture) They will eat the leaves and so your boxwoods won't be able to do photosynthesis anymore.
Let's get back to our central question: How can you recognize the larves? It's very simple: they're flashy green with black points and stripes. Sometimes they even have a little yellow color. And how can you notice their presence? You can't miss it: your boxwood will show yellow spots full of dead, eaten leaves. (see picture below)
More information under the picture.
Another way to notice their presence is to look for their nests. These are small, white webs - like a little cobweb - that are often constructed between young shoots. (see picture)
A very important detail are their eggs: these are very small, brown granules of about 1 mm diameter. Shake your boxwood and listen if you hear small granules fall. If yes, then you have a serious problem: you'll have an army of caterpillars in a few weeks...
So, I recommend you to read the rest of this blog....
Box tree moths usually lay eggs 3 times a year: during spring, summer and autumn. So always check your boxwoods for any caterpillar/moth.
When you're finally sure that your boxwoods are being attacked by the box tree moth larves, then you must take action! Let's get over to the solutions!
What can you do against them?
There are a few solutions against the box tree moth but not every solution is good for environment. For example: when you use toxic products to kill the larves, then these become poisonous. So when the birds pick them to feed their young, you'll not only kill the parents, but also the young birds! Small actions can have terrible consequences! That's why I've selected the eco-friendly solutions you.
1. Take them away manually
This solution is very efficient when box tree moth larves are not yet numerous. But, be careful! Caterpillars can be toxic for humans. So always wear a pair of gloves before you touch them and always wash your hands afterwards! Otherwise you could have an allergic reaction or even worse.
This has been the best solution for me. Rockdust is a powdery substance made out of finely crushed rock. It's commonly used as a soil conditioner but you can also use it to kill the larves.
Perfect, isn't it? It will eradicate the larves and fertilize your boxwoods!
But, how do you apply it?
To use it, you'll need a powder duster. Just fill the recipient with rockdust and nebulize generously your boxwoods.
Note: DO NOT add water or any other liquid to the rockdust!
Make sure to spray everywhere: on the leaves, under the leaves, in your boxwood, on new shoots (where the nests are, remember?), a.s.o.
You'll need to repeat this method after every rain shower! Otherwise the rain will wash away the protecting layer of rockdust.
Rockdust is - normally - available at your local gardening store.
3. Bacillus thurigiensis
Bacillus what? Bacillus thurigiensis is a bacterium that is often used as a natural pesticide. And so, it can also be used against the Box Tree Moth.
The proteins of the Bacillus thurigiensis will attack the degestive system of the larves and paralyze it so that they won't be able to eat anymore and finally die.
How to apply it:
Mix the Bacillus thurigiensis powder (available at your local gardening store) with a little bit of water (follow the exact instructions on the product itself) and spray it over your boxwoods. That's all you need to do!
4. Pheromone traps
Pheromone traps can be used for different purposes: to show their presence and to trap the male moths.
How do they work? These traps use the female moth hormone called Pheromone to attract the male moths. And so, these moths won't be able to fertilize the female ones.
This solution only works for the moths, not for the larves!
5. Nematodes steinernema carpocapsae
Nematodes are the last solution of my blog. These can be applied the same way as the Bacillus thurigiensis: just add a little amount of water to the powder and spray it over your boxwoods. Always check the instructions on the product itself for any specification.
Nematodes are available at your local gardening story but can only be kept for 2 weeks after purchase.
Nota Bene: biological products...
You may have noticed that I didn't mention any biolgical product. This is for a reason. Even though products can be 'biological', this does not guarantee that it hasn't any incidental consequences for the environment. The biological products against the box tree moth contain a chemical substance called 'spinosad' which is very dangerous for water organisms, bees, and other flying insects because it's a toxic insecticide. So please don't use biological products! The bees and other organisms will thank you!
I hope you learned more about the box tree moth and its larves. I wish you good luck and let me know if these 5 ways kept them away from your boxwoods! See you soon!