Chestnut leaf miner

Chestnut leaf miner is a worrying issue that is affecting a huge number of horse chestnuts, one of our most popular landscape trees.

During the summer the miner (caterpillar) lives in the leaf and eats it from the inside, leaving the characteristic brown blotches. As their numbers increase the blotches spread – which is why trees that are heavily infected turn brown during mid-summer.

If you hold an infected leaf up to the sun you may well see the leaf miner moving around - if you then carefully pull the leaf apart with your nail you should be able to expose it. 

The leaf miner is now pretty much endemic across the southern half of the country, so any remedial work needs to be aimed at on-site management rather than eradication. Research is being carried out into developing pesticides - both eco-friendly and conventional - but it seems unlikely that these will prove to be effective given the scale of the task. As the miner over-winters in fallen leaves, the best course of action is to remove and burn the leaf litter in the autumn. This will break the disease cycle and while it is likely that the trees will become infected again from other sources, it will at least slow down the onset of re-infection.