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Notebook · Guide 8 October 2026 · seasonal

Box blight or box tree caterpillar? Telling them apart

Webbing and striped green-and-black caterpillars mean box tree caterpillar. No webbing, but brown leaves dropping and black streaks on stems, means box blight. The fixes differ.

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Your box hedge has gone brown in patches and you need to know why. There are two usual suspects, and they need different responses. Box blight is a fungal disease. Box tree caterpillar is the larva of a moth that eats the leaves. The quickest test takes a minute: part the foliage over a brown patch and look inside. Webbing and caterpillars mean caterpillar. No webbing, with black streaks on the young stems, means blight. Some unlucky gardens have both.

01At a glance

  • Box tree caterpillar: fine webbing, greenish-yellow caterpillars with black and white stripes, chewed leaves. Damage mainly from March to October.
  • Box blight: leaves turn brown and fall, leaving bare patches. Black streaks on young stems. Worst in warm, wet weather.
  • Caterpillar fix: pick them off by hand, and check again and again from early spring.
  • Blight fix: in dry weather, cut out affected growth, clear fallen leaves, bag and bin it, and improve airflow.
  • Both: catch them early. Damage spreads fast.

02Side by side

Box tree caterpillar

  • Webbing over the feeding area.
  • Caterpillars: young ones are greenish-yellow with black heads. Older ones grow up to 4cm and are greenish-yellow with thick black stripes and thin white stripes along the body.
  • Leaves eaten and webbed together. Patches of dieback, especially obvious on clipped shapes. Caterpillars can also strip bark.
  • Timing: at least two generations a year. Damage mostly from March to October. Small caterpillars spend the winter hidden between leaves webbed together.

Box blight

  • No webbing, no caterpillars.
  • Leaves turn brown and drop, leaving bare patches.
  • Black streaks on young stems, with dieback.
  • In wet weather, white spore masses may appear on the undersides of infected leaves.
  • Timing: can be active all year, but worst in rainy, warm, humid spells.

Still not sure? The RHS suggests putting a few affected leaves in a plastic bag with moist tissue for a few days. White fuzz on the undersides points to box blight. Pink spore masses point to Volutella blight, a less serious disease of box.

03If it's box tree caterpillar

  1. Pick them off by hand wherever it's practical. Pull the webbing apart to find them.
  2. Check from early spring, before the overwintering caterpillars grow big enough to do noticeable damage.
  3. Keep checking from May onwards. Moths flying in can lay eggs on box that looked clean in spring.
  4. Look again in late September and October. By then most of the population are small, young caterpillars about to settle in for winter.

Pheromone traps tell you whether the moths are about and how active they are. They don't control the caterpillars. The RHS notes that a mixed nematode product has some effect, but nematodes can also infect other creatures, so use them with care.

04If it's box blight

Work in dry weather, so you don't spread spores.

  1. Dig up and destroy badly affected plants, especially ones that don't matter much to you.
  2. On plants you want to save, cut out the affected parts.
  3. Clear fallen leaves from the middle and base of the plants, and strip off the top layer of soil underneath.
  4. Bag everything and bin it. Don't compost it. The fungus can survive on fallen leaves for up to six years.
  5. Disinfect your shears between plants, and between gardens.
  6. Feed cut-back plants with a general-purpose fertiliser to help them recover.

Then make blight's life harder: clip less often, give hedges a rounded top rather than a flat one, avoid watering over the top, and mulch at least 5cm deep between November and February to cut down rain splash.

05Should you give up on box?

If you want certainty, grow something else. Common box and the classic edging box 'Suffruticosa' are highly susceptible to blight. Buxus microphylla cultivars are generally less susceptible, but nothing stops the caterpillar except watching for it.

The RHS's box alternatives include yew, which takes all soils except waterlogged ones and recovers well from hard pruning, privet, osmanthus, podocarpus and boxleaf honeysuckle. Japanese holly (Ilex crenata) is widely planted as a substitute but was the least successful in the RHS survey, struggling in wet winters and hot, dry summers. None is a perfect match for box.

Save your money
Don't buy a pheromone trap expecting it to save the hedge. It only tells you the moths are about. Your eyes do the real work.
Don't spray blight as a first move. The RHS recommends against fungicides and says they're unlikely to work without the hygiene steps anyway.
Before replanting a lost hedge with more box, price up an alternative. Replanting a highly susceptible box in a blight-hit garden is money you may lose twice.

Before handling clippings or planting where children or pets play, check the safety flags on our box, yew and privet profiles.

How we checked this

Every care and safety claim on this page is verified against horticultural and veterinary sources.

Sources: RHS — Box blight · RHS — Box tree caterpillar · RHS — How to choose box alternatives

Checked 8 October 2026. If our advice ever conflicts with the RHS, believe them and tell us.