Horse Chestnut Leafminer [ Cameraria ohridella ] is an invasive pest that has appeared and spread over large parts of the UK in recent years. It targets mainly Horse Chestnut trees. This tiny moth creates mines in the leaves of the trees, these reach very high numbers making the leaves appear white before they turn brown. This gives the tree the appearance of a tree in the autumn. The tree is weakened producing smaller conkers but the pest does not appear to kill the trees. However it does make the trees more prone to diseases and infections. There can be 3-4 generations of Horse Chestnut leafminer moth a year from April-October but the main season of damage is June - September. The moth larvae pupate in the leaf mines.
How to control
There are currently few control methods available to control the Horse Chestnut Leafminer. The best practice to reduce Horse Chestnut leafminer numbers is by removing fallen leaves in the autumn and to destroy the leaves. This kills a large number of the pupae in the leaves. This can be combined with placing Horse Chestnut Leafminer pheromone traps in the trees from May-September. These traps will attract and catch huge numbers of Horse Chestnut Leafminer moths reducing their ability to breed and lay eggs.