Horse-chestnut Leaf Miner
The only other damage likely to be confused is by a fungus (Guignardia aesculi), but damage caused G. aesculi produces large red-brown blotches that tend to be concentrated at the tips and margins of the leaflets, superficially resembling leaf mines. Unlike C. ohridella mines, the blotches caused by the fungus are often outlined by a conspicuous yellow band and do not appear translucent when held up to the light. Later, Guignardia infections produce tiny black pimples (pycnidia) on the browned parts, mostly on the upper surface. Leaflets severely affected by Guignardia roll upwards longitudinally and, like leaves infested by C.ohridella, may fall prematurely. Unlike C.ohridella, the damage, although unsightly, occurs after most of the growth of the tree has taken place. Guignardia leaf blotch is widespread and common in the southern half of England, becoming less frequent northwards.
The mines produced by Cameraria are very distinctive, often clearly restricted to the area between veins in the leaf. The moth itself, although very pretty is only 4mm long (wingspan 8mm) so easily overlooked, therefore the best method of monitoring this species has been to record the occurrence of the mined trees.
- Forestry Commission Exotic Pest Alert - Horse chestnut leaf miner