From a distance, horse chestnut trees seem to be turning a lovely autumn colour, but a close look at the leaves tells a different story.
It looks very much as if these leaves are affected by the caterpillar of the leaf-mining moth, which burrows into the leaves. Each caterpillar living inside the leaf produces a blotch that can be the size of a ballpoint pen lid. Blotches are initially pale, but turn brown. Get enough leaf mines and the tree can turn so brown that it looks like autumn has come early.
It does not kill the tree. There is mixed evidence of the effect it has on the trees, but it does reduce the photosynthetic capacity of the tree - meaning the tree produces less food for itself.
It has only been in Britain since 2002. It spread from London at a rate of about 30km per year and is now found across most of England and Wales.
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pity about the disease - hope the damage is not going to be very bad
Thank you all for your lovely comments and favs, they are very much appreciated.
It seems that this disease doesn't actually kill the trees, but does weaken them.
Ian