How to deal with box tree moth in your garden

Like many gardeners, I watched in despair this summer as the leaves of my topiary box balls became skeletonised, turned brown, and began to fall off. At first, I assumed the culprit was the dreaded box blight. But I was surprised. Growing my box in pots, I thought I’d reduced the risk thanks to better air circulation around the plants and watering from the base.

But on closer inspection, I noticed leaves stuck together with webbing – and even tiny droppings. The real problem wasn’t blight at all. It was the box tree caterpillar, and there were plenty of them.

What is box tree moth?

The box tree moth (Cydalima perspectalis) comes from East Asia and was first spotted in the UK in 2007. By 2011, caterpillars were appearing in private gardens across the Home Counties, and the moths quickly established themselves in London and beyond.

Many gardeners, myself included, weren’t fully aware of the threat until recently. But the record-breaking heat of this summer, with four separate heatwaves and temperatures regularly exceeding 30°C, created perfect breeding conditions for insects generally. The box tree moth spread further than ever.

So, is it time to give up on growing box altogether? Damp weather encourages blight, hot summers favour caterpillars… it feels like something of a no-win situation. But don’t give up just yet. There are several strategies to protect your plants.

How to control box tree moth

1. Pheromone traps

   

   Pheromone traps attract and catch the male moths, reducing the chances of successful mating and helping to keep populations in check. The traps should be set from March to October, around 1.5–2m above the ground in the open. Each pheromone lure lasts for about five weeks, so you’ll need to refresh them throughout the season. As well as reducing numbers, they’re a useful way to monitor whether the moths are active in your garden.

2. Removal by hand and pruning

   Checking your plants regularly is one of the simplest ways to keep on top of box tree moth. If you only have a few plants, you can pick the caterpillars off by hand as soon as you see them. It’s not the most pleasant job, but it can be very effective if you catch them early. For heavier infestations, pruning is often the best approach. Cut out the worst-affected shoots to reduce the damage and expose any hidden caterpillars.

   Whatever you remove, make sure it’s disposed of properly. Bag up all prunings and caterpillars and put them straight in the household waste. Don’t add them to your compost heap, as the larvae can easily survive and find their way back into your garden.

3. Biological control (nematodes)

   

   If you’re looking for a wildlife-friendly way to deal with box tree moth, nematodes are one of the best options. These are microscopic organisms that naturally parasitise the caterpillars, killing them without harming birds, bees or other beneficial insects in your garden.

   Nematodes are supplied live, usually in a packet that you mix with water and apply as a drench to your box plants. Because they are living organisms, they need to be stored carefully in the fridge and used before the expiry date. Timing is also important: nematodes work best when the soil and air are warm enough (above about 12°C) and when the caterpillars are small and actively feeding.

   Follow the instructions on the pack closely and be prepared to reapply through the season as new generations of caterpillars emerge. When used correctly, nematodes can be a highly effective and environmentally responsible way to keep box plants healthy.

4. Bacterial insecticides

   You may come across products such as TopBuxus XenTari while searching for biological solutions online. These sprays use a bacterial insecticide based on Bacillus thuringiensis, a naturally occurring bacterium that targets caterpillars but is considered harmless to birds, bees and other beneficial wildlife.

   However, it’s important to know that XenTari is not currently approved for amateur gardeners’ use in the UK. As with all pesticides, it must be licensed by the relevant authorities before it can be sold to home gardeners. Until then, it remains unavailable through legal retail channels here, even though you may see it discussed or advertised on some websites.

5. Plant-based insecticides

   One option available to home gardeners is BugClear Ultra 2, a plant-derived insecticide that’s approved for use in organic gardening. Unlike true biological controls such as nematodes or Bacillus thuringiensis, BugClear Ultra 2 relies on natural ingredients — pyrethrins (extracted from chrysanthemum flowers) and rapeseed oil — to tackle a wide range of pests.

   The spray works on contact, killing or smothering pests such as aphids, whitefly, red spider mite, mealy bugs, scale insects, and now box tree moth caterpillars. Because it acts quickly, you’ll usually see results within hours of application.

   As with all insecticides, timing is important. To avoid harming pollinators, spray early in the morning or later in the evening when bees are not active, and always choose a still, dry day to prevent drift. Follow the instructions on the label carefully for dilution rates and frequency of use — repeated applications may be needed through the summer to keep caterpillar numbers under control.

Whatever method you choose, consistency is key. Caterpillars hatch in successive waves throughout the summer, so a single treatment of any of the above isn’t going to be enough. Plan to repeat applications several times during the growing season. You could even try cycling between different approaches to hedge your bets. At the same time, give your plants a regular feed with a balanced fertiliser. While this won’t stop the moth, it will help your box recover more quickly from damage and stay stronger in the long run.

Alternatives to box

If you decide the battle against box tree moth isn’t worth it, you’re not alone. Many gardeners are now looking at substitutes that can give the same neat, evergreen look without constant worry. The RHS has been running trials at Wisley and consulting with professional gardeners and members to find the most reliable alternatives.

One early favourite, Ilex crenata (Japanese holly), showed promise for its small, box-like leaves. However, in practice it struggles with our cold, wet winters and increasingly hot, dry summers. Fortunately, other plants are proving more successful. Varieties of Lonicera (honeysuckle) and Ligustrum (privet) are standing up well. Both are evergreen, tolerate regular clipping, and can be trimmed tightly to create the tidy shapes that make box so popular. Their small leaves and strong regrowth after pruning mean they capture much of the character of traditional box.

The RHS continues to test and recommend further options, and their research is well worth following if you’re considering a change. You can explore their latest findings and alternative plant suggestions here.

Final thoughts

For now, I’ve decided to give my box plants another chance – but this time with a proper plan in place. Last year, I left it too late and didn’t apply nematodes until August. By then the caterpillars had already done their damage. Next year, I’ll be keeping a close eye on the plants from early spring, stepping in quickly with treatments before the problem gets out of hand.

Looking after box may feel like a lot of effort these days, and the outcome certainly isn’t guaranteed. But gardening rarely comes with guarantees. What it does give us is the chance to learn, adapt, and try again – and that’s part of the reward. With vigilance, the right tools, and a bit of persistence, there’s still every reason to enjoy healthy, thriving box plants in our gardens.