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How to treat box tree caterpillar

Updated: 22 October 2026

You have the parcel, or you are about to mix one, and the hedge already shows silk and pellets in the centre of the bush. This is how to treat box tree caterpillar with the products in this comparison, without pretending a trap empties the leaves. Seven amazon.co.uk listings were saved on 20 October 2026. There was no lab test. The rows are on the [box tree moth killer comparison](/hub/pest-control/box-tree-moth-killer). Check the label and the HSE database before any spray. EBTS UK and BBC Gardeners' World describe effective Btk products as professional-only, so a mixing line on a listing is not permission. A qualifying purchase can earn a commission at no extra cost to you.

You have the parcel, or you are about to mix one, and the hedge already shows silk and pellets in the centre of the bush.

Our top picks

BuxusPro BuxTrap box tree moth trap

Best overall

BuxusPro BuxTrap box tree moth trap
8.3/10about £16.99
View offer
Gifts by L Green Guard box treatment, 50 g

Rank 2

Gifts by L Green Guard box treatment, 50 g
8.5/10about £9.79
View offer
BuxusPro BuxBarrier spray, 500 ml

Alternative

BuxusPro BuxBarrier spray, 500 ml
5.6/10about £19.99
View offer
On this page
  1. 1.Confirm caterpillars versus blight
  2. 2.Mix or ready-to-use application
  3. 3.Trap placement basics
  4. 4.After rain and a later generation

Confirm caterpillars versus blight

Box tree caterpillars are green, often with dark stripes, and they feed inside webbing with black frass. The Royal Horticultural Society describes that pattern. Box blight is different: brown leaves and black streaks on stems, without a crowd of caterpillars in silk. Green Guard's title mentions both, which is how the wrong job gets sprayed. Open the bush. Larvae and fresh webbing mean caterpillars. Blackening stems and no caterpillars mean stop and identify blight before you buy a moth trap. On two or three balls you can reach, pull the webbing and repeat on following days, because one pass misses larvae in the crown.

Mix or ready-to-use application

For Green Guard or the £14.99 Habitat Harvest powder, the listing rate is 5 g in 2 litres for about 30 m². The claim of up to 300 m² is that rate repeated, not a licence to tip the sachet into one can. If the label and the listing disagree, follow the label. Wet the inside of the canopy, because the caterpillars sit in the silk. BuxBarrier is 500 ml, already mixed, and it does not give a 30 m² figure. One buyer says water after two or three days. Another sprayed caterpillars directly in dry weather and saw no kill. Buxus Support prints a similar 5 g mix, and reviews describe a biofungicide, so do not copy that routine unless the label matches the pest. Do not spray open flowers where bees are working.
BuxusPro BuxTrap box tree moth trap

Testsieger

BuxusPro BuxTrap box tree moth trap
8.3/10about £16.99
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Trap placement basics

A trap is a calendar, not a wash for the leaves. For the BuxTrap, hang it about 1 to 1.5 m up, with about 5 cm of water and a drop of detergent. The No More Mr Nice Guy kit says March to October, about 3 cm of water, a hang height of 1.5 to 2 m, and one trap per 0.5 acres. Use the height on the trap you bought. One trap near the box matches a garden. The refill replaces a lure and does not include a bucket. Intervals on the listings run from five weeks to eight. Write the date you opened the lure on the trap. An empty trap does not prove the hedge is clear if you can already see caterpillars. The sequence is on box tree moth trap and spray.

After rain and a later generation

A Habitat Harvest review says you repeat the treatment, especially if it rains. EBTS UK links feeding with warmer conditions, around 15 °C, and notes that rain and sun shorten what is left on the leaf. Southern Britain commonly sees more than one generation, so a tidy bush in June can be webbed again in late summer. Look again seven to fourteen days after the first spray, and after heavy rain. Both 50 g caterpillar listings claim a shelf life of more than three years. Store spare lures below 30 °C if the refill pack says so. If you need a ladder, an authorised professional product, or blight and defoliation are both severe, stop and get a contractor. A later generation is a reason to inspect, not to double the dose.

Common questions

How do I mix 5 g in 2 litres?
Use the spoon in the Green Guard or £14.99 Habitat Harvest pack and the rate on the label, which the listings state as 5 g in 2 litres for about 30 m². Stir it so the powder is not a lump at the bottom, and spray the inner leaves as well as the outside. If you only wet the green surface, caterpillars in the webbing can miss the coat. A stronger homemade rate is what a Green Guard reviewer found too costly, and it is not the instruction.
When should I spray after rain?
If rain has fallen on a fresh coat, treat that coat as lost and look at the label for a repeat. Buyers on the Habitat Harvest and Green Guard files both tie a second spray to wet weather. Pick a dry stretch so the leaves stay wet with the product rather than with rain. Do not spray in the middle of a shower and expect the 30 m² claim to hold.
Will the trap tell me when to spray?
It tells you adults are flying, which is the warning, not the cure. The BuxTrap listing is about early detection. If you already have webbing, spray or hand-pick on the schedule the foliar label allows, even if the bucket is empty. A catch after a quiet week means keep inspecting. It does not mean the larvae have gone.
What if the hedge looks dead after I spray?
One Habitat Harvest review reported hedging brown and dead five days after a treatment that was applied as the packet said. That is a single report, not the average of the 4.2 score, and it is serious enough to stop and look at the stems. Green tissue under the bark suggests the plant may still be alive. Black stems and no caterpillars point you toward blight. Do not immediately buy a second, different powder and layer it on.
Should I spray Buxus Support the same way?
Only if the label in that parcel is for the problem you have. Reviews and pack notes describe a biofungicide, and one buyer still had caterpillars and eggs two weeks later. The 5 g line on the listing is not proof it is the caterpillar powder sold under the same brand. Read the sachet before you copy the other Habitat Harvest routine.
When do I stop and call someone?
Call a professional if you need a ladder, if the only effective Btk option is a professional product, or if blight and a heavy caterpillar attack are both in the hedge. Hand picking is reasonable on a few plants you can reach. It is not a plan for a tall screen. Authorisation sits with the product name on the HSE database, not with the amazon title.

Related pages

Box tree moth killer buying guide

Bt versus a natural spray

Box tree moth killer

Best box tree moth killer UK: who each listing suits

Box tree moth trap and spray: moths, then larvae

Sources

Public UK sources used for this comparison. Shelf prices, stars and review counts are the amazon.co.uk figures captured for these seven listings on 20 October 2026. A listing is not treated as HSE authorisation.

  1. RHS box tree moth (retrieved 20 October 2026)
  2. EBTS UK box moth and caterpillar (retrieved 20 October 2026)
  3. BBC Gardeners' World box tree caterpillar (retrieved 20 October 2026)
  4. HSE garden and home pesticides (retrieved 20 October 2026)
  5. HSE pesticide product database FAQ (retrieved 20 October 2026)