Categories
Advice

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 from Amazon.

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.

109 replies on “Five Ways to Beat the Box Tree Caterpillar”

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?

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.

Thank you so much for this – my boxus is brown entirely now with eaten leaves! I noticed the characteristic droppings and saw a striped caterpiller a few weeks ago but I didn’t know about it so didn’t link it to the spreading brown and dying leaves!
I just sprayed Xentari, absolutely drenched it, and am just crossing my fingers to see if it will recover. I thought it was completely beyond recovery but I have hope now, as I don’t think the bark is being eaten (it is still green). Will see..!

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.

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

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.

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

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.

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

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?

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.

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.

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.

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

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.

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!

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.

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 !

Thank you SO much, Achille. I have one small box plant left on my balcony out of five attacked by box caterpillars over the last few years. Today I tried your tip and upended the plant in a bucket of water, the pot supported by two lengths of wood for two hours. It just fitted the bucket.
When I removed the plant and checked the water, LOADS of dead caterpillars lay at the bottom. I counted as best I could and there are more than 50. I had no idea there were so many. Result!

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?

I have followed all instructions and think all caterpillars are dead. My box hedge is now parched due to the hot weather. As I gave them a final spray with Xentari today, when will it be safe to water them? I don’t want to kill them through lack of water after all this😬

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?

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?

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?

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

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

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?

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.

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.

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?

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?

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.

Hedge is full if caterpillars already. As there’s too much rain in the forecast I will cut all the sticky leaves out and get rid of as many as I can in the process. Is thyme oil a repellent and can I make any from my thyme plants?

Would spraying with a coffee ground solution work? Would it mask the smell of the box and maybe make the taste of the leaves less palatable?

Hello I have had problems with the caterpillars for about 3yrs now I use Xentari which does usually work this year I am having problems maybe because it has been so wet it’s very difficult to treat as doesn’t seem to stop raining !

Hi, can you use the xentari and the nematodes at the same time for a dual-pronged attack on the caterpillars? If yes, should the nematodes be poured on first? Then wait a day … then spray with the xentari? Or what would you suggest?

I’ve never tried this so wouldn’t know. Best to ask the manufacturers advice. Personally I would use one or the other. They are both very effective if used correctly.

Why doesn’t Xentari have a license for amateur use in UK gardens anymore if it is as harmless as you describe?

Good question and I don’t have a simple answer. DiPel, which is widely used by professionals, is based on the same Bacillus thuringiensis (or Bt) bacterium. It is allowed in organic farming as a insecticide because Bt is a natural, non-pathogenic bacterium that is found naturally in the soil. I do the know the company who sell the product have applied for a license and they are confident it won’t be long until it’s approved.

I. Have never heard of the box caterpillar before not being a gardener but then I noticed my hedge had seemingly just died. I have cut all the plants back as far as possible for me (I am 81 years old) I can’t dig out the roots. I haven’t seen this infamous creature so didn’t know what it could do.
What should I do now.

We sprayed our extensive box hedging monthly, April-September last year and the year before and kept damage to a tiny minimum. This year, despite upping the regime to once a fortnight, there is some significant infestation and damage. Interestingly, no moths in our traps. The worst damage is in the more sheltered parts of the garden. I wonder if our caterpillars are becoming resistant to Topbuxus Xen Tari. We’re feeling pretty resigned to losing some of our hedges this year.
We understand, from chats, that the National Trust are not going to plant any more box but are looking to alternatives. Good luck, everybody out there!

The caterpillars you are seeing now could be ones that overwintered on the plant. Not heard of them building up a resistance to Xentari. Just seems to be a lot of them this year.

Ah, yes – thanks. No moths in the traps does suggest our caterpillars are over-wintered ones, rather than this season’s, doesn’t it. We’ll press on with the spraying and also feed and hope for some recovery eventually. Should feeding start now, James?

Does Xentari, kill just the caterpillar or does is it absorbed by the leaves which then poison the caterpillar when it feeds?

The Bacillus thuringiensis bacterium are absorbed into the leaves. When the caterpillar eats the treated leaves it gets into their digestive system. After a couple of days the caterpillar will be no more.

Have just found our two Japanese Box hedges full of webbing inside the bush and outside, however cannot find any caterpillers at all..just lots of white clumpy webbing…is this likely to be Box Moth?? The bushes still look healthy. I wondered if maybe the caterpillers haven’t hatched yet.

If there’s webbing then they would have hatched. Caterpillars do hide themselves well or sometimes the birds eat them. Keep an eye out for small areas of nibbled leaves and then you’ll definitely know it’s the box tree caterpillar.

I have a cloud tree which I always thought was ilex crenata (I inherited it when I bought the house). It now has a heavy infestation of box tree caterpillars. Is it in fact box?? I’m confused. Thanks for all the advice. I have ordered some Xentari. Meantime I have been jetting the tree with water as this makes the caterpillars appear on strings. I then dispose of them.

I haven’t heard of of box tree caterpillar on ilex crenata so maybe it is
Buxus. Or possibly another caterpillar? Appearing on strings is not something I’ve seen the box tree caterpillar do. They normally hide in webbing amongst the leaves of the plant.

Sadly, I have an infestation on a large old box hedge. Over the last week I have spent many hours squashing caterpillars. I have noticed that there is also a lot of snails on the box head. Are these also a pest to my box hedge and should I be removing them? Or what I am really hoping is that they are eating the eggs from the moth/catterpiller and helping my fight against these pests .

James, many thanks for highlighting this issue. We have a fair amount of box hedges, balls, spirals etc. We were waiting for the box-tree moth and first found it about four years ago. It now seems endemic in the area as friends are also suffering. We cut the box as normal in May (weather permitting) and then spray with bacillus thuringiensis. This seems to resolve the problem very effectively and we haven’t found it necessary (so far) to respray.
We are also providing it to several friends and neighbours.
You mentioned DiPel, which I have found available in agricultural quantities. It also claims to be effective against other caterpillars. Are you aware of other products that contain bacillus thuringiensis as the effective ingredient and ship in more reasonable quantities – 20-50g. We’re trying to spread the word in Herts but many gardeners would find the costs prohibitive.

DiPel is the one used in the agricultural industry. Comes in a large tub. Topbuxus Xentari is the main one packaged into the smaller quantities. Both use the bacillus thuringiensis bacterium as the main active ingredient.

Wish I’d seen this 2 weeks ago , been through 3 hedges and 4 potted box .

I have seen a few birds in and out so hopefully there is hope of nature picking this pest off before it devastates the whole country

Hi there – I have a lot of box in my cottage garden and this year have developed quite a lot of box caterpillar damage (and some blight) across hedging and topiary which we have treated a few times in desperation with Xentari. Usually I will have trimmed all the box around this time of year but unsure whether to do this and risk spreading any further damage? Any advice most welcome. thank you Judi

If you mean is the biological insecticide poisonous to cats then I think it isn’t. The manufacturers say it’s safe for birds to eat the dead caterpillars. Always good to check with them first though if you are unsure.

I had an infestation in a box hedge near my pond.A couple of the caterpillars fell into the pond and were eaten by newts,unfortunately the newts died the following day.

Thank you for your very informative article. We have had a significant infestation in many of our hedges and topiary, I assume from caterpillars that over wintered. Hand picking was quite an eye opener (caution when squeezing as the juices travel )!
I have pheromone traps which seem to be working in the last week and have sprayed with XenTari 3 times in the last month. I have also been out at night with a head torch zapping dozens of moths with a “fly executioner” as we seem to have a lot of moth activity (presumably from pupae that survived the sprays ?)
DIPEL seems more cost effective but is a different strain BT “Kurstaki ABTS-351, to XenTari BT “Aizawai” ABTS1857, is this as effective ??
Do you know how long it usually takes for the new eggs to hatch as caterpillars ? so i can try and predict the next wave or caterpillars ?

I would say you are doing more than enough Mike. I only spray when I see caterpillar activity (nibbled leaves). No point otherwise because the caterpillars have to eat the treated leaves for the biological insecticide to work. It’s usually 3 or 4 times a year. Make sure you’re only disposing of box tree moths as there are a lot of beneficial native moths that are important to protect. DiPel works as well as Xentari. When you see box tree moths in your trap is an indication of a new wave starting in about 2-3 weeks.

Oh my goodness, I’ve got a real battle on my hands ( sprayed all six of my Boxhedge with Xentari on Sunday and caterpillars still alive .Should I respray so soon ,and
Should you wear a mask when spraying ?

Takes a few days for the bacteria to get into the gut of the caterpillars and do their worst. But good news is that the caterpillars will stop eating your Buxus in the meantime. Re-spray in 10 days if required. I always prefer to wear a mask.

Hello James ,am I right in thinking that Toboxus Xentari has to be ingested by the caterpillar and therefore won’t kill the eggs laid by the moth?

Thank you, James, for this informative article.
We’ve just arrived at our French house, having been away 3 weeks, to find the majority of our box hedging, box balls and box cloud suffering from box caterpillar damage, ranging from totally bereft of green leaves to minor evidence.
Xentari and traps ordered.
Am I correct in assuming spraying the hedging with only brown leaves is a case of closing the stable door after the horse has bolted and I should concentrate on the rest?

We have an infestation of this and there is no way I can pick them all out, plus there are thousands of eggs. If we dig up the buxus and dispose of it I assume this is the only way? The hedges are near enough dead too 🙁

The biological insecticide Xentari works very well. Just need to apply it at the right time (when the caterpillars can be seen eating the leaves). I use it about 3 times a year on the Buxus I work on. The dead looking Buxus may well recover if the caterpillars are kept under control. Digging up is the last resort.

I’ve noticed a musky smell around my buxus during caterpillar season.
Are you familiar with this, is it something that the plant or insect emits?
I had originally thought that it could be the very first signs of box blight.

I’ve not noticed it with the caterpillar but I have occasionally smelt it when the Buxus is not looking in the best of health. Haven’t worked out why yet. Doesn’t seem connected to insects or blight.

We have 2 mature and well established box hedges that have been infested with box caterpillar. Didn’t realise what the problem was initially! We got the pheromone trap a couple of months ago and that has definitely reduced the number of moths – not seen any for over a month – but we’re still picking caterpillars off the hedges! Some sections are badly affected and completely stripped of leaves, but other parts are ok – so it’s not (yet) affected the whole bush. Have ordered the nematodes to try and stop any further damage. My question is, I’ve not trimmed the hedges this summer as I was nervous about causing more stress or damage to the plants – but the unaffected parts are growing strongly and they’re becoming very untidy and blocking the path. Am I ok to trim them back or should I wait? Any advice gratefully received! Thank you 😊

Very informative. Thank you James.
I’ve bought a trap and the moths have entered the trap. What should I do with these moths. Should I have added some water in the base?

Why plant box hedging if its so amenable to the Box Caterpillar? Spraying poisons of any sort should be avoided from the outset. A spray like Topbuxus Xentari, apparently only targets and is lethal to the Box Caterpillar and not to other bugs and birds, is to be questioned and regarded with the greatest of suspicion especially as the Topbuxus Xentari chemical spray isn’t, by all accounts, registered in the UK. If part or all of your box hedge succumbs to caterpillars that’s Mother Nature ain’t it? Bite yer lip and tuck in yer wobbly indignation when you clap eyes on the Box Caterpillar’s banqueting on you box hedge, and rethink gardening strategy creatively. Instead plant another species of hedge or fill in box hedge gaps with other flowering hedging species. Our planet is already poisoned enough effecting so many fauna and flora survival.

I have beautiful Buxus hedges along the perimeter wall of my roof terrace, since 2017. In 2020 the first infestation of Box Moths / Caterpillars appeared. I’ve done tonnes of research and experimentation. Here’s what I have found… The traps are not the solution on their own. They will catch some if you’re lucky. I’ve often seen up to 8 swarming around my trap but not actually falling in. The design of the traps need modifying. They are however useful as a way to know there are moths around in order to prepare for battle. The best method for catching the moths (if you’re hedges are in close proximity to a window in your house/garage/outbuilding and you hang a trap close to your hedges and the window …) is to open a window and turn on a bright light! The moths will fly into your room. It’s easy to catch them by hand and dispose of any way you wish. EASY! I’ve caught about 40 this year. Much more effective than relying solely on the trap. To eradicate the caterpillars use Xentari. It works. Make sure to spray inside the hedges as well as around the outside. Manage this throughout the annual caterpillar seasons around the weather. It’s not always easy but try spray when it looks dry for several days. OTHER THINGS: water your hedges at the bottom (i stick a hose in) to avoid blight. Give your hedges a good shake whenever possible! A female ready to lay eggs will fly out and any breeding taking place will be interrupted. Check the hedges regularly by picking through the stems looking for caterpillars. Remove any and kill them and prepare your Xentari spray solution! Always keep several Xentari boxes handy. Delivery can take ages and sometimes stock is not available! Don’t bother with Nematodes – the shelf life and specific weather requirements makes them very impractical. By doing all this you will be able to compete with me (self proclaimed ‘best Buxus hedges’ in Surrey).

Leave a Reply

Your email address will not be published. Required fields are marked *

%d bloggers like this: