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Horse chestnut leaf miner (Cameraria ohridella)

The larvae of the horse chestnut leaf miner bores within horse chestnut leaves, eventually causing them to drop and harming the tree and leaving it vulnerable.

The horse chestnut leaf miner larvae 'mine' into horse chestnut leaves to feed.

Credit: Adrian Davies / Alamy Stock Photo

The adult is a very small and difficult to identify moth.

Credit: Chris Robins / Alamy Stock Photo

Brown spots on the leaves show where the leaf miner has fed.

Credit: Joe Bates / WTML

Quick facts

Common name: horse chestnut leaf miner

Scientific name: Cameraria ohridella

What does it affect?: horse chestnut and its hybrids

Areas affected so far: across the UK

Origin: south-eastern Europe

What does horse chestnut leaf miner damage look like?

Symptoms include:

  • Tracks within the leaves left by the feeding larvae.
  • Dry, crisp and brown leaves.
  • Premature leaf drop from the tree, it might be completely bare by autumn.

What is the horse chestnut leaf miner?

The horse chestnut leaf miner is the larvae of the moth Cameraria ohridella. The adult moths are tiny at about 4-5mm in length. They are a rich brown colour with bright white chevrons edged with black.

In early summer, the adult female lays up to 180 eggs on newly opened leaves. The hatched larvae feed on the leaves, going through several growth stages where it will grow from 0.5mm to 3.5mm. The larvae then pupate and can overwinter in the leaf litter until they emerge as adults in early spring to lay eggs on that year’s fresh leaves.

Credit: Patrick Nairne / Alamy Stock Photo

What happens to the tree?

When infestations of horse chestnut leaf miner build up, all of the leaves of the infected tree can become brown and shrivelled as the larvae eat all of the inner leaf material. Over years of sustained infestation, the tree can become weakened.

Where has the horse chestnut leaf miner impacted?

So far, the horse chestnut leaf miner has spread from England to Wales and more recently into Scotland as far as the central belt.

How did the horse chestnut leaf miner get here?

The first horse chestnut leaf miner record in the UK was taken in 2002 in England. The moth probably originates from natural stands of horse chestnut in its native southern Europe and it was first seen attacking trees in the 1970s.

It has since spread quickly, likely through the accidental transport of pupa in dead leaves and leaf litter, and through the transport of moths in vehicles. Some of the bigger jumps in populations have been attributed to imports of infested horse chestnut saplings.

Credit: Naturepix / Alamy Stock Photo

What impact will the horse chestnut leaf miner have?

While it doesn’t kill trees, years of leaf miner infestations can leave horse chestnuts weakened. This can leave the trees in a vulnerable state where they are more susceptible to diseases like horse chestnut bleeding canker.

There’s no getting rid of this pest either; there might be fluctuations in populations but it’s here to stay.

What are we doing about it?

To combat the spread of pests and diseases like horse chestnut leaf miner we have:

  • Developed a UK and Ireland Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK.
  • Lobbied the government to improve biosecurity at border points to stop new pests and diseases entering the UK.
  • Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.

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