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Let me guess, you’ve woke up today, looked out of your window only to see MORE of your beloved box hedging wither away into nothing but skeletal shells. Well, you’re not the only one!

The last two years I’ve seen more of it than ever before. Instead of planting more box, I’ve started replacing it with Euonymus instead, and so far it’s doing the trick!

However, you’re here to try and save your current box hedge; not re-plant.

Box hedge caterpillars (Cydalima perspectalis) are a nightmare to deal with.

For such miniscule creatures, they consume a power. Without acting fast to kill their population in your hedges, they’ll defoliate plants in weeks. They’re greedy little critters.

Spotting them is difficult enough so manual removal will be laboursome and tedious.

Likely to be inefficient too.

The most effective ways to get rid of the box hedge caterpillar is chemical or biological treatments.

So, without rambling on too much, lets take a look at some box caterpillar treatments.

Let’s delve in to some of the best box caterpillar treatments

Topbuxus Xentari

topbuxus xentari where to buy

If like me you are sick and tired of going out there, rooting around yours or a customers box hedge and manually picking out these green caterpillars then I may have just the answer. Topbuxus Xentari box caterpillar killer claims to be the ultimate game changer.

This product is a biological insecticide, and claims to be 100% safe to humans, animals, bees and even birds that eat the actual box caterpillar.

With its powerful, naturally active ingredient, Bacillus thuringiensis var. aizawai (Bta) this will save your box hedging from the ghastly box tree caterpillar.

Although this popular insecticide hasn’t been approved in the UK just yet, it has been approved in quite a few European countries.

This is because Topbuxus XenTari is currently going through the rigorous UK registration process and is expected to be approved mid 2024. When buying the product here you are buying from a company based in Holland.

This is the ultimate organic method to destroy entire populations of the box tree caterpillar.

The commercial alternative is Dipel, but that requires professional certification in pesticide application. PA1 and PA6 certifications are required to buy Dipel in Britain.

The difference between Dipel and Xentari is the strain of Bacillus thuringiensis used. Dipel uses the kurstaki (Btk) strain.

This (Xentari) uses the Bt subspecies of Aizawa (Bta) which specifically targets caterpillars, whereas the Btk strain targets butterflies too. In that respect, Xentari is the most targeted biopesticide suited to treating box hedges and trees for a caterpillar infestation.


One purchase contains 5 sachets, and each sachet treats up to 30m2.

Mix one sachet with 3L of water and spray your box hedge plants. If you’re using a 5L pump action sprayer or larger, and don’t use all the solution in one go, it keeps for 3-months provided it’s kept at room temperature.

That’s handy since you need to give your box hedges three treatments per year because the box caterpillars go through three cycles.

This is not a contact insecticide, It’s a toxin to caterpillars!

Treat the leaves, particularly the underside of leaves where insects feed. Caterpillars ingest the toxin (Bta) and it causes internal blood poisoning. Caterpillars stop feeding within one hour, and die within 2 to 3 days.

What I find great about this method is that is not toxic to other wildlife, so even if birds continue to feed on the caterpillars, it causes them no harm.

Same with bees and other beneficial insects. Only the box tree caterpillars are poisoned.

For best results, use Topboxus Xentari in conjunction with Topboxus Health Mix. It’s a foliage fertilizer that helps box plants recover from the stress of insects feeding on the leaves.

Nemasys Box Tree Caterpillar Nematodes

how to use nemasys

Nematodes are microscopic worms, different ones target different insects.

The ones you want to use to control caterpillar infestations are Steinernema as they release bacterium that’s toxic to caterpillars, but harmless to everything else.

Trouble is, entomopathogenic nematodes are mostly suited to soil borne pests.

The box tree caterpillar is particularly sneaky because they leave their eggs on the underside of leaves, and protect them inside a cocoon of fine webbing.

Nematodes have their work cut out hunting these things down, then getting inside them. That’s why you’ll need repeated applications even when you’re releasing millions of these onto your box plants per application!

With Nemasys, you get enough to treat 60m2 three times over, one treatment applied every 7-days over three weeks. Don’t mistake the three sachets as being capable of treating 3 x 60m2 areas.

Once the nematode is inside the caterpillar, it releases a toxin called Xenorhabdus spp. It’s parasitic to insects and they will stop eating your box plant, then the nematode will eat the caterpillar from the inside out and reproduce inside the caterpillar too.

They don’t eat your plant, and they’ll continue to hunt down other caterpillars and their larvae.


To apply, temperatures should be a minimum of 12 degrees and the soil around your plant kept moist.

The best time to apply this is in the evening when the sun’s going down, the temperature cooling, and importantly… no overnight rain expected. That’d wash the nematodes off the leaves and we don’t want that!

If using a watering can, use an extra course watering can rose. If you plan to use nematodes repeatedly, a nematode applicator makes life easier.

Provanto’s Ultimate Bug Killer


how to use provanto bug killer box caterpillar treatment

Provanto have a couple of products that’ll kill caterpillars. One’s better though and that’s the concentrate.

Ultimate Fruit and Vegetable Bug Killer concentrate.

It’s a contact insecticide, meaning that for it to work, it needs to come into direct contact with the caterpillar.

The Ultimate Bug Killer comes in a ready-to-use spray bottle and doesn’t have the force required to penetrate the webbing caterpillars hide within. It’s unpredictable at best.

For maximum efficiency, buy the concentrate and mix it yourself following the instructions on the label.

For it to be effective, you really need to be applying this with enough water force to penetrate the webbing they hide in.

Even if it is on the leaves though, it’ll still kill box tree caterpillars once they feed on any treated leaves. Preventing further damage, that’s best done with a forceful jet spray to ensure fast contact.

Provanto’s Ultimate Fruit and Vegetable Bug Killer contains the same active ingredient (Deltamethrin) as the Provanto Ultimate Bug Killer sold in spray bottles, just as a concentrate.


Once you’ve mixed it to the required ratio, use a pressure sprayer or backpack sprayer with a standard flat fan nozzle.

A single treatment lasts for 30-days. 30ml makes 1 litre and it lasts up to 4 weeks.

Deltamethrin is part of the pyrethroid family, the synthetic version of pyrethrins. It is indiscriminate and highly toxic to any insect and wildlife it comes into contact with. Apply this with care!

Vitax Py Bug Killer Concentrate

how to use py bug killer for box caterpillar

Vitax PY bug killer is a broad spectrum insecticide. It’s indiscriminate and extremely potent.

The active ingredients used are 10g/l of pyrethrins (cypermethrin), and 40g/l of piperonyl butoxide (PB).

Piperonyl butoxide on its own does nothing, but blend it with cypermethrin and it enhances the potency.

So much so that it comes with a warning to limit applications to twice yearly and with a minimum 10-day interval between treatments.

It’s specifically designed to cull insects in vegetable gardens. Mainly, aphids and caterpillars.

Similar to any contact insecticide though, all the leaves need to be thoroughly coated to ensure the pests ingest this.

Since it’s broad spectrum and not target specific, it’s toxic to wildlife including birds and bees.

Be careful of nearby plants and wildlife when applying this!


Only 5ml per litre of water is required so a 250ml concentrate will be plenty of ammunition to go at your box hedge plants with.

5ml treats up to 20m2 and it should be applied using a pressure sprayer, not a watering can.

Spray in the morning or late evening when the weather’s dry making sure to get to the underside of leaves.

As it is potent and comes with a warning to only use twice per year, going forward, this can be applied to box hedges in April before they get attacked by the buxus caterpillar, then at the end of the season as a preventative measure.

If you’re treating a really bad invasion and one treatment doesn’t work, reapply after ten days.

Resolva Bug Killer

how to use resolva bug killer

When you need to move fast, this is the big gun to hit your box plants with.

It’s is a pyrethroid insecticide, the active ingredient is lambda-cyhalothrin and this is the only pesticide in the UK consumer market that contains it.

Once applied to the plants leaves, it’s ingested by the caterpillar.

It disrupts the nervous system, causing paralysis and eventually it’ll kill them.. Gruesome right?

The fast acting nature of it means as soon as it’s consumed by the caterpillar, they stop eating the leaves on your box plants and eventually die and fall off.

The only drawback you’ll find with this is that it does not last long. Once applied to the plant, it has an efficacy of just two weeks.

Repeat treatments will be needed. Particularly for treating box hedge caterpillars given that they have three life cycles.


Resolva is available as either a 1L ready to use spray bottle, or as a concentrate.

If using the concentrate, be careful with the dilution ratio. The label says it’s safe to use on a wide variety of plants, and edible crops.

Too strong a dose though, it is likely to become harmful.

In terms of the volume of spray required, 300 to 500 ml will treat up to 10m2. It’s recommended to spray this in the early evening, and that’ll be because lambda-cyhalothrin breaks down in sunlight.

It’ll have the best impact when applied in low light levels and when the temperatures are cooler.

So, hopefully this article on Box Caterpillar Treatment has helped you get a better idea on how to deal with the dreaded caterpillar.



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