Boxwood moth caterpillars – also called boxwood moth caterpillars – can strip the leaves of your boxwood plant or hedge.
In my neighborhood there are rows of dead boxwood hedges in many front yards. All the leaves are brown and if you look closely you can often still see the caterpillars on them.
It is a relatively new pest that came from Asia via Europe and arrived in the UK in 2007. It is spreading rapidly around the world to the United States, Canada and other places.
This year I discovered boxwood caterpillars on all of my boxwood topiaries, including my beloved topiary spiral. This is the most expensive plant in my garden and also an eye-catcher.
My topiary spiral in happier times.
How to recognize damage to the boxwood moth caterpillar
The damage begins in spring with the appearance of boxwood caterpillars. Typically they have spent the winter wrapped up in their silk fabric and protected in your boxwood plant.
As your plants sprout new green growth, you will see darker green or brown-gray patches where the caterpillar has damaged that new growth.
Get closer and you’ll see a web of white or silver tissue with dying foliage and a caterpillar inside.
Look for areas where there is no new growth (see photo above). If you look closely, you will see dead or dying leaves in these areas. A larger stain can be seen in the photo below.
What do the boxwood moth caterpillars look like?
Box moth caterpillars have citrus green and black stripes that run the entire length of their bodies. They have black heads and are usually protected by the fine tissue around them.
The boxwood moth caterpillar
What eats the caterpillars of the boxwood moth?
We are all encouraged to create wildlife-friendly gardens so predators can eat our pests. It makes gardening easier and protects the environment.
I recently interviewed Helen Bostock, RHS Senior Wildlife Advisor, about gardening for biodiversity. She explained that slugs help our compost piles work better.
If you have birds and ladybugs, they will eat most of your aphids. So as long as you’re willing to tolerate a few nibbled leaves, you can ditch the chemical sprays and let nature do the work.
However, no one is suggesting that you take this approach with boxwood caterpillars. As they have only recently arrived, there are currently no natural predators for them in the UK. There were some early reports of sparrows, starlings and blue tits starting to feed on them in the UK, although not in sufficient numbers to contain the spread.
In Asia, Asian hornets eat boxwood caterpillars, but these would cause other problems if we imported them here.
This is how you get rid of boxwood moth caterpillars
If you don’t want to harm other insects in your garden, you need to control boxwood borer caterpillars with biological control. You can get nematodes (Nemasys Fruit & Veg is a popular brand for this purpose). Please note that links to Amazon are affiliate links, see disclosure.
You must read the nematode instructions carefully and follow them carefully. For example, you often cannot keep them for long and may need to refrigerate them.
There is also a product called Top Buxus Xentari that several professional gardeners around the world have used successfully. It is safe for bees and birds.
It is a bacterial insecticide with an active ingredient based on Bacillus thoringiensis Substitute Azawai. Another product with Bacillus thoringiensis as the main active ingredient is now available in the UK as PlantPro BuxRevive. This is what I’m currently using to combat the caterpillars on my boxwood.
You can find professional treatment by searching “professional boxwood borer treatment” online. Make sure they use products that minimize harm to other insects or wildlife.
Any insecticide that works against multiple pest species is also likely to impact the natural balance of pests and predators in your garden. Therefore, avoid all-purpose sprays if possible. If you use one, make sure you use it on a calm, dry day so the spray doesn’t drift.
You will need to repeat each treatment several times throughout the summer.
Please note that links to Amazon are affiliate links, see disclosure. Other links are not affiliate links.
Prune and feed the box plants
Several professional gardening enthusiasts have pointed out that trimming the box means cutting off (or halving) some of the caterpillars. This is not a cure, but a useful way to reduce the number.
So we cut all of our topiaries. Always bag the clippings and dispose of them – do not leave them lying around or throw them into the compost heap.
I was also advised to feed the plants. Again, this is not a cure, but it will help plants recover faster and should minimize damage.
Healthy, well-established plants always resist pests and disease better than struggling plants or new, recently planted plants.
Do boxwood moth caterpillars eat other plants?
No, they don’t. If you see caterpillars on your other plants, they are not boxwood borer caterpillars.
But in the end, you shouldn’t plant boxwoods
Unfortunately, the best way to prevent boxwood moth caterpillars and boxwood blight is to stop planting boxwood moths.
There may be a blight-resistant variety of boxwood in the future. And treatments like TopBuxus Xentari are also likely to be licensed more widely.
That’s a shame, because the boxwood is such a great plant, especially for topiaries. There has been a lot of discussion about the best alternatives to boxwood in the gardening world. And everyone was pretty disappointed with the performance of Ilex crenata, the plant most similar to boxwood.
You can trim conifers to shape, and some have naturally sharp shapes that look like topiaries. See how conifers can transform your year-round garden.
I have also used privet, holm oak and holly in my own garden. I bought them as young plants and had them topiarized, which was cheaper than buying them ready-made. Learn how to buy a sensational topiary on a medium-sized budget.
If you live in the UK and have just discovered box borer caterpillars in your garden, let the RHS know by completing the survey on this page.
Pin to remember how to get rid of boxwood borer caterpillars
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