Horse chestnut leaf-mining moth

Horse chestnut leaf-mining moth has spread rapidly across since it was first identified as present in Britain from Wimbledon in 2002. It had probably been present in that area for at least a year before it was discovered. The effect on the appearance of horse chestnut trees in the second half of the summer by the leaf-mining moth can be profound.

Cameraria ohridella (horse chestnut leaf miner). Credit: RHS/Entomology.

Quick facts

Common name Horse chestnut leaf-mining moth
Scientific name Cameraria ohridella
Plants affected Horse chestnut, Aesculus hippocastanum, and some other species/hybrids
Main symptoms White or brown blotches on the foliage
Most Active June to September

What is horse chestnut leaf-miner?

Horse chestnut leaf-miner is a small moth with caterpillars that feed inside the leaves, causing brown or white blotch mines to develop between the leaf veins.

Symptoms

It is usually easy to spot trees affected by the leaf-mining moth, especially as the season progresses.

  • Horse chestnuts produce normal foliage and flowers in the spring and the first signs of leaf-mining usually appear during June in the UK
  • Elongate blotches, at first white but later turning brown, develop on the foliage from June onwards
  • Caterpillars, or circular pupal cocoons, can be seen within the mined areas if the leaf is held up to the light
  • By August, most of the leaf area may be occupied by leaf mines, giving the impression that the tree is dying, although it will survive
  • Heavily infested trees will drop their leaves early, however research has shown that this has almost no effect on the growth rate or health of trees

Control

Non-chemical control

  • Collecting and burning fallen leaves in autumn will reduce the overwintering pupae
  • Alternatively, the leaves can be composted in sealed bags which should be kept closed until the following July, by which time any adult moths will have emerged and died
  • A pheromone trap that attracts male moths is available from Oecos. In some circumstances this may reduce the mating success of the moth and therefore the level of infestation
  • These measures can delay the build-up of damage during summer but is only worthwhile for isolated trees where most of the fallen leaves can be gathered up
  • Some chestnuts, such as Aesculus indica, A. × neglecta and A. chinensis, are not attacked or suffer only slight damage. Aesculus indica is the closest in size and appearance if a replacement tree is required for A. hippocastanum

Chemical control

  • Spraying is not feasible on large trees and no suitable chemical treatments are available to home gardeners for this leaf-miner

Biology

New to Britain in 2002, this moth has become widespread in England and is spreading in Wales. It may spread throughout most of the UK. 

  • The tiny brown (10 mm wingspan) and silver adult moths lay eggs on the foliage
  • After hatching, the caterpillars enter the leaves and eat the internal tissues
  • There are usually three generations during summer, and, by August, the foliage may be extensively damaged, leading to early leaf fall
  • This moth overwinters as pupae in the leaf mines

Survey

Monitoring the long term impact of horse chestnut leaf mining moth on the health of trees is key to understanding this pest. Through citizen science, gardeners can help with this work. Conker Tree Science is monitoring horse chestnut (Aesculus) trees for the presence of leaf-miner damage and are inviting members of the public to help by sending in their reports.

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  • PY avatar

    By PY on 11/10/2014

    At the back of my garden, Hounslow, Middx, is a large conker tree with what Looks like this leaf mining moth infestation. The leaves are green early spring then rapidly turn a horrible brown colour, looking diseased. This year it seems to have passed over into my garden and affected my apple and pear tree both of which had developed brown leaves by summer and for the first time have not produced fruit. I'm not sure who owns the conker tree but is it best that it is cut down? Otherwise I think my smaller fruit trees will just suffer. Apart from anything they look awful with shrivelling brown leaves in the summer. Will it be the same every year? Will I need to cut down my own trees? If I do I can't replace with new ones as they are likely to get infested in the same way I assume.


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  • Jander avatar

    By Jander on 01/10/2014

    Yes, it’s such a shame that this grand tree is being impacted in such an unsightly way. We live in a small village in Sth Cambridgeshire (moved here in 2003) and there was no infestation at that time. In fact, I don’t think we saw this problem manifest itself until around 2007 at the earliest. In 2006 we had two examples on the front of our property in close proximity to one another, one of which showed severe decay in the trunk and was leaning precariously over towards our garage. South Cambs Council gave us approval to remove this tree (we are in a tree conservation area), but it’s interesting to note from photos I took at the time that the other tree was in full, unblemished leaf, and this was the end of August! I wonder if nature will take its course, and eradicate this pest naturally over time. Comments anyone?


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  • davydoy avatar

    By davydoy on 11/08/2014

    We have an Avenue of Horse Chestnut trees which all seem to be badly affected by this moth. The trees appear to be very unsightly and devoid of conkers this year. Glad to read that they will not die.


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