Five Ways to Beat the Box Tree Caterpillar

You will know if you have box tree caterpillar in your garden because of the damage it can cause. Buxus can be stripped of their leaves in a very short period of time.

box tree caterpillar damage

If left untreated, then the box tree caterpillars will eventually kill the plants. But there is a good chance the Buxus will recover if the unwelcome pests are removed early, before too much damage is done.

Box tree caterpillars are relatively easy to spot when you know what to look out for. The obvious signs are small patches of nibbled leaves.

On closer inspection you should find densely woven webbing and below this small grit-like black balls. This is caterpillar poo! The box tree caterpillar will probably be protecting itself within the webbing amongst the box leaves.

Having the webbing as protection and wrapping itself in Buxus leaves makes treating the box tree caterpillar difficult.

Insecticides such as Bayer’s Provanto Ultimate Bug Killer are often ineffective against the caterpillar’s defences.

Personally I’m not a fan of contact insecticides. They are fairly indiscriminate about which bugs they target so you risk killing a lot of beneficial pollinating insects in the spraying process.

Here are four other ways to beat the box tree caterpillar that I prefer to recommend:

Box Tree Moth Pheromone Traps

Targeting the source can prove effective at reducing caterpillar numbers. The box tree moth trap works by attracting the male moth using a female box tree moth pheromone. The male moths in the trap will not have a chance to breed.

Half filling the trap with water and a dash of washing up liquid is an effective way to ensure the male moths won’t be flying again.

The pheromone traps act as an early warning system indicating when the male box tree moths are active and another breeding cycle is about to start. This is a good time to spray your box topiary and hedging with my next recommendation.

Biological Insecticide

Biological insectides based on the Bacillus thuringiensis bacterium are the most effective at the targeting the box tree caterpillars.

Topbuxus Xentari is the one most talked about and can be purchased direct from the producer. Usually next day delivery if ordered before 2pm.

I should add Xentari doesn’t have a license for amateur use in UK gardens. However it is widely available to buy online.

Topbuxus Xentari

A caterpillar will soon stop feeding when it eats a box leaf treated with biological insecticide, and will be no more within a couple of days.

Other insects are not affected by the biological insecticide as it only targets the caterpillars eating the treated leaves. I’ve also been told birds are not harmed when eating the dead caterpillars.

Apply the biological insecticide as soon as you see caterpillars or your pheromone traps start to fill up with male box tree moths.

The treatment is only effective for about 10 days as it is broken down by UV light so you may need to reapply more than once when the caterpillars are active.

Nematodes

Nematodes are tiny worms that are mixed with water and applied to the box plants using a watering can, hopefully making contact with the box tree caterpillars in the process.

The nematodes maybe small but they soon make short work of the caterpillars and gruesomely use their bodies to reproduce until there are none left.

Nematodes must be applied in the right way to be effective. They are UV sensitive so application in the evening is best. Avoid dry periods as moist conditions help and keep an eye on the temperature. If it falls below 12C then the nematodes won’t work.

Nematodes don’t store well. They can be kept in a refrigerator for 4 weeks but best to order them only when you know you have time to treat the box.

Hand Picking

Picking off the caterpillars by hand and ‘disposing’ of them is the best way to control their numbers. But also the most time consuming.

Dropping the caterpillars in a bucket of water is a good way to say goodbye to them if the thought of squashing caterpillars is not appealing.

Our native birds are starting to become interested in the caterpillars as a food source but not enough to make an impact. This could be because box leaves have toxins in their leaves that must make the caterpillars taste awful.

I am hoping that now more people are aware of box tree caterpillar and are taking action, we may be able to reduce their population in future years and reduce the devastating damage they have been causing to our box topiary and hedging.

Using box tree pheromone traps will have some effect. But combine this with hand picking or spaying with a biological insecticide such as Xentari and we may have a real impact on the box tree caterpillar.

47 responses to “Five Ways to Beat the Box Tree Caterpillar”

  1. Great advice. I’ve been using Xentari and it worked very well however a week or so later I spotted more alive caterpillars so further treatment every week or so if required.
    Once a bush is consumed by the caterpillars do we know they will will come back to life?

    1. Thanks Sunny. Yes, you will need to spray a few times to ensure all the box leaves are treated. A box plant will recover if the caterpillars have only stripped its leaves. But if they have continued to feed on the bark of the plant then unfortunately the chances of recovery are reduced.

    2. Also note xentari isn’t licensed and allowed to be sold or used in the UK

  2. The ordinary topbuxus copper sulphate (I think) works well too, as a feed it’s advertised as, and as something the caterpillars die eating once the leaves have absorbed it.

  3. Hi James, I bought Nematodes but then got scared of using them as I read on a USA site that they actually caused Buxus to die. Can you clarify? Thank you,
    Jennifer

    1. I’ve not heard of that before Jennifer. I would have thought it was unlikely as the nematodes seek out the caterpillars and should have no interaction with the buxus to cause it to die. If applied correctly according to the instructions that come with the Nematodes then I can see them doing any harm.

  4. Thank you very much for this advice – my box trees were devastated in less than 2 weeks – I will follow the advice given and let you know how I get on. Ilka

  5. Thanks for this advice. When the box starts growing again, do you cut off the dead bits?

    1. Thanks Sarah. If the growth is dead (brittle twigs without any flexibility and snap easily) then no point keeping and best to remove. Other defoliated stems that are still flexible can sometimes recover and hopefully you will start to show new leaf growth soon.

  6. I need cheap remedy I have a bad back from picking off catapillars and can’t afford to continue buying xentari.

    1. You could try box tree moth pheromone traps? Please use my TODMAN10 discount code at Dragonfli for 10% off – https://www.dragonfli.co.uk/collections/box-tree-moth/ This discount code also works for their box tree caterpillar nematodes 🙂

  7. This is a very useful article, Thanks. I have a question. I’ve used other nematodes successfully but as these are sensitive to temperatures below 12C how can they survive for 4 weeks when refrigerated?

    1. Thank Roger. I’m not sure of the science behind this but I do know nematodes need to be kept cool (not frozen) to survive longer, which is why refrigeration is recommended. I’m guessing it’s a bit like refrigerating food to keep it longer. Once out in they open air the microscopic worms need to find a host quickly (i.e the caterpillar) to release their bacteria otherwise they will die. The optimum temperature for them to be active is above 12C.

  8. Native birds do seem to enjoy these caterpillars. Our hedges have been alive with great tits and coal tits stripping these pests out of them… and it has made me hesitant to spray to be honest. Sadly I suspect I no longer have a choice and its the only chance to save the hedge.

    1. Yes, I think native birds are finally developing a taste for the box tree caterpillar. I only use a biological insecticide to spray as it doesn’t harm the birds when they eat the dead caterpillars.

  9. Hi, Do you have any recommendations for fertiliser or the like to encourage regrowth of leaves after the caterpillars have gone?

    1. Hi does white vinegar.. Soap and water work

  10. I have just ordered some moth traps in the hope of saving my box hedge. An individual box plant In a pot elsewhere in the garden Has been stripped. I am wondering at what height and position I should place the box traps. Please advise.

    1. Hang the trap in a tree or hedge about 5-6ft from the ground, within a 10ft vicinity of the Buxus.

  11. I have some neem oil and dish soap handy, I was thinking of trying it. The caterpillars are actually on a Witch Hazel, not a Box, but I’ll report back if I have success!

    1. Update : they all died and fell off my shrub in less than an hour! I like neem for all soft bodied pests, I guess I’ll add these to the list.

      1. Thank you James for all your inspiring work and all your photos of topiaries that I am pleased to follow on insta.
        I do have some potted boxes.
        When the caterpillars arrive I plunge the entire foliage upside down in a large bucket of water for 2 hours and it’s sooo effective !

      2. I am concerned about my box trees bring infested with caterpillars so I treated the trees with xentari. The sad bit is that the rain had suddenly poured down so I covered the box trees with plastic. Is it safe to do so? Will I be inviting more shelter for caterpillars?

        1. Don’t leave the plastic on for too long as this will create perfect conditions for box blight

      3. I wish I had been so lucky. Need oil hasn’t worked for me.

    2. Hi , could I ask if you mixed the oil and washing up liquid together .. if so what quantities? Tia

  12. Thanks for advice James. I started using the traps last year and they’re excellent as is Xentari. I’m prepared this season having been caught unawares last year. Recovery has started but any advice on the completely bald patches? Will they ever green up?

  13. I have a mature box hedge 25m x 1.5m x1.5m which has been severely attacked by caterpillars. I’ve used Exentari twice now in the last fortnight – it’s easy to apply and at first the results look good, but in a mature hedge, the caterpillars can be deep in the foliage and seem to survive if they are not near the surface leaves and reappear after a week or so. Any suggestions?

    1. Need to keep treating regularly

  14. Is the biological insecticide safe for bees…we have beekeepers next door!!

  15. I have got some Xentari to treat my box. But it’s June, so it’s due a trim. Which should I do first, trim or treat?

  16. Hello,
    I’ve been reading about Trichogramma parasitic wasps to help control box moths. Do you have any experience of using it? Many thanks.

    1. No experience of the wasp but always cautious about introducing a new insect to fight off a pest.

  17. I’ve been spraying my hedge with diluted Ecover washing up liquid once or twice / week and it seems to be working.

  18. I treated my hedges in June with Nematodes which worked well, then I took my eye off them and they’ve been decimated whilst I was away. I’m treating the surviving ones again but how should I deal with the rest? They are totally shrivelled up. Should I cut right back to the wood and hope they regrow next year or dig them up?

    1. If the caterpillars have just stripped the plants of their leaves then there is a possibility the Buxus will recover. Leave until next Spring and hopefully you may see some regrowth. Established box is a tough plant.

  19. I have given up and taking out my wedding cake 4 tier buxii (hope that’s a word) and my playing card shapes.
    Can I dig in the leaves left around the ground.

    1. As long as they are free of box blight. Blight spores can remain in compost heaps or soil up to 6 years.

  20. I have a boxum that was attacked by caterpillars in the summer but I got rid of them as soon as a noticed they were causing chaos. They stripped the outer leaves and those stems are now brittle. I do however have new growth coming from the centre of the plant. Do I cut off all of the dead brittle parts to allow the new growth to flourish?

    1. If the stems are brittle and snap then they are dead so best to remove.

      1. When can I stop spraying? And I heard I have to burn the cuttings and debris as the moths can fly up to 2 miles so no point in tossing them in the woods. Is that correct?

        1. I would stop spaying in October as the box tree moth breeding cycle will finish about then. Caterpillars probably won’t feed on cuttings so no problem putting them in the woods- if you have permission to do so.

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