Horse chestnut leaf-mining moth
Horse chestnut leaf-mining moth has spread rapidly since it was first identified as present in Britain from Wimbledon in 2002. The effect on the appearance of horse chestnut trees in late summer can be profound.
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 horse chestnut leaves, causing brown or white blotch mines to develop between the leaf veins.
Nearly 900 insects, including some flies, beetles, moths and sawflies create leaf mines as larvae, more information about some for these insects can be found at The leaf and stem mines of British flies and other insects
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
- Elongate blotches, at first white but later turning brown, develop on the foliage
- 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 affected trees can drop their leaves early, it has been found that this has almost no effect on the growth rate or health of trees, although conkers may be slightly smaller
Horse chestnut trees appear to tolerate the moth and so control is not necessary or in most cases practical.
- Leaf miners can be part of a healthy balanced garden, most species will have natural enemies including parasitoid wasps. Birds such as blue tits can sometimes open mines to consume the larvae within and this can be quite noticable in some areas for this moth
- Collecting and burning fallen leaves in autumn may 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 several suppliers including dragonfli and Harrod Horticultural. In some areas where the moth is uncommon 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 affected or suffer only slight damage. Aesculus indica is the closest in size and appearance if a replacement tree is required for A. hippocastanum
- Pesticide spraying is not feasible nor desirable on large trees and no suitable pesticide treatments are available to home gardeners for leaf-miners
New to Britain in 2002, this moth has become widespread in England and is spreading in Wales. A few sightings have also been reported in Scotland. It may spread throughout most of Britain.
- The small 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
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