Box Tree Moth Caterpillar Nematodes (Steinernema mix)

If you've noticed unusual webbing on a clipped box ball, leaves stripped to skeleton form, or the unmistakable sight of pale-green caterpillars with black heads working their way through your topiary — this is what you're looking at. The Box Tree Moth (Cydalima perspectalis) has become one of the most serious threats to British box gardens of the past decade, particularly across the South, and it's spreading.

The good news: nematodes work. The RHS has now confirmed what biological control specialists have been recommending for years — that nematode treatments significantly reduce larvae numbers, and properly timed, they can save a box hedge or topiary specimen from the worst of the damage.

This pack contains a Steinernema feltiae / Steinernema carpocapsae nematode mix — two complementary species working together against the caterpillars at the most vulnerable stage of their life cycle. Each pack treats approximately 60 sqm of box hedge or topiary. Available in 1, 2, or 3-pack quantities, supplied through our partner Ladybird Plant Care — specialists in biological pest controls, chosen because their approach mirrors our own.

Spotting the pest

Catching box tree moth early gives you the best chance of saving the plant. Look for:

• Pale yellow eggs in clusters on the underside of leaves, often near the outer growth
• Caterpillars — pale green with black heads and dark stripes, growing up to 4cm long
• Webbing between leaves and twigs, often the first sign noticeable from a distance
• Defoliation and dieback — caterpillars work their way inward, sometimes stripping a plant from the inside out before the outer canopy looks affected
• The adult moth — brown with white-edged wings, around 4cm wingspan, often resting on or near box plants

By the time webbing is visible, you typically already have a serious infestation. Worth checking your box plants regularly through spring and summer rather than waiting to see damage.

How nematodes work against box tree moth

The nematode mix in this pack — Steinernema feltiae and Steinernema carpocapsae — are microscopic organisms that seek out the caterpillars and infect them naturally, halting feeding within hours and ending the larva's life cycle within a few days. Crucially, they're harmless to bees, butterflies, ladybirds, hoverflies, birds, pets, children, and the wider garden ecosystem.

RHS Entomologist Stephanie Bird has confirmed: "Nematodes can be a useful addition to the gardener's armoury for control of box moth caterpillar." A recent RHS study found they considerably reduce larvae numbers — bringing the overall pest population down by affecting this critical life stage.

When and how often to treat

Box tree moth has two generations per year, so for proper protection treatment is needed at two points in the season:

• Spring treatment — typically late April to May, targeting the first generation of caterpillars
• Midsummer treatment — typically July, targeting the second generation

For each treatment window, ideally apply three doses, two weeks apart. This gives the most reliable control because nematodes are short-lived once applied, and successive applications catch caterpillars hatching at different times.

Air temperature needs to be 12°C or above for the nematodes to be effective — apply on mild days, and ideally in the cool of evening rather than the heat of midday.

How much to order

Here's an important practical point: nematode packs only stay viable in the fridge for 2-3 weeks. So we'd recommend not buying all three doses for a treatment window at once. Instead:

• Order the first two doses at the start of your treatment window (the 2-pack quantity is sized for exactly this)
• Order the third dose a couple of weeks later, timed to arrive when you need it

This way nothing goes to waste, and your treatments are always with the freshest possible product. For larger box collections covering more than 60 sqm, scale the quantities accordingly — one pack treats roughly 60 sqm of plant material.

What else to do alongside

Nematodes are most effective as part of a wider approach. Some additional steps that genuinely help:

• Hand-pick caterpillars wherever you can see them — especially in the early stages of an infestation
• Remove and bin (don't compost) any leaves with heavy webbing — this physically reduces the pest population on the plant
• Check the underside of leaves for egg clusters and remove these by hand where possible
• Pheromone traps can be useful for monitoring adult moth activity (not for control, but for knowing when caterpillars are about to appear)
• Open up the centre of dense topiary a little after pruning — better airflow makes the plant less hospitable to caterpillars and easier to inspect

The combination of nematodes for the larvae you can't see and hand-removal for the ones you can is significantly more effective than either approach alone.

Ordering and despatch

Because these are live biological controls, we don't keep them on standing stock — they're ordered in fresh through Ladybird Plant Care so they reach you at peak effectiveness.

• Order by 10am Monday for despatch the same week
• Orders placed after 10am Monday will despatch the following week
• Dispatched directly by Ladybird Plant Care — you'll receive tracking from them

Worth bearing in mind when planning a treatment cycle — give yourself a few days' grace, particularly for the first dose.

Full application instructions come with your pack. You can also download the detailed instructions here.

Help the RHS track the spread

Box tree moth is still spreading across the UK and your sighting genuinely helps the RHS monitor where it's reaching and how rapidly. If you've spotted moths, caterpillars, or damage, please consider filling out the RHS Box Tree Moth Survey. It only takes a few minutes, and citizen-science contributions like this are how we collectively understand and respond to garden pests.

About Ladybird Plant Care

Ladybird Plant Care are specialists in biological pest controls — gentle, naturally-derived solutions for problems that have traditionally been tackled with chemicals. We stock their range because their approach mirrors our own: work with the garden, not against it, and trust the wider ecosystem to find its own balance.

A note for box-loving gardeners: if your hedge or topiary is significantly damaged, don't write it off. Box is remarkably resilient — with the moth controlled and good aftercare (a feed, a mulch, patience through one growing season), most plants recover their form within a year or two. The hardest part is acting quickly enough to stop the damage before it gets ahead of you.

Live biological products cannot be returned. Please order only when you're ready to apply within the next few days, and ensure you have suitable conditions (temperature above 12°C, active pest presence) for treatment success.

1 x sealed pack (or 2 or 3 packs, depending on size selected) of
Steinernema feltiae / Steinernema carpocapsae nematode mix.
Application instructions enclosed.
Each pack treats approximately 60 sqm.

STORAGE BEFORE USE:
- Refrigerate immediately on arrival
- Use within 2-3 weeks of receipt
- Do not freeze
- Avoid direct sunlight or heat

APPLICATION CONDITIONS:
- Air temperature must be 12°C or above
- Apply between late April and early September only
- Box hedge or topiary must be moist before treatment
- Apply in evening or cool part of day, never midday heat

TREATMENT SCHEDULE:
Box tree moth has TWO generations per year, so two treatment
windows are needed:

Spring treatment (late April to May):
- First-generation caterpillars
- Apply 3 doses, 2 weeks apart

Midsummer treatment (July):
- Second-generation caterpillars
- Apply 3 doses, 2 weeks apart

ORDER STRATEGY:
- For each treatment window, order the first 2 doses initially
- Order the third dose 2-3 weeks later, timed to arrive when needed
- This prevents waste due to the 2-3 week fridge life

ALONGSIDE NEMATODES:
- Hand-pick visible caterpillars
- Remove and bin (don't compost) leaves with heavy webbing
- Check undersides of leaves for egg clusters and remove by hand
- Consider pheromone traps for monitoring adult moth activity
- Open up centre of dense topiary for better airflow