This is a relatively new problem in the UK, the first reported cases being in London in 2002. It has been recorded that there has been a rapid spread of this moth across the country to date.
The cause is a moth which lays its eggs on the leaf veins and when the larvae hatch out they feast on the upper and lower parts of the leaf by means of making burrows internally within the leaf.
Eggs are layed from April to August so several breeding cycles can occur in just one season.
Leaves start to get brown blotches and as the infestation increases the mines merge together causing the whole leaf to brown and curl and eventually drop.
The tree will look Autumnal far too early in the year.
Conker size may be affected
The brown leaf blotches may be mistaken at first for the fungus Guignardia aesculi, however the fungus blotches are distinguishable by a yellow band around each blotch whereas the blotches from the leaf miner have no yellow band.
Prevention and control
It has been suggested that as the foliage is destroyed prematurely during the season that the tree may not have be able to photosynthasise adequately to maintain vigourous tree growth.
However, there has been little evidence to substantiate this claim, and trees seem to grow back just as strong and well the following year showing no dieback or reduction in the upper tree canopy.
It also may be thought that prolonged moth attacks over several years may weaken the tree leaving it susceptible to other diseases, but again nothing concrete has been proved of this as yet.
Recently the most effective way of preventing and managing the moth infestation is to hang moth traps in the canopy containing a pheromone lure. This has proved to be very effective in trapping hundreds of adult moths.
Blue tits are also happy to feast on this insect, so hanging nesting boxes suitable for them on the tree is also an effective and natural way of curbing the multipication of the moth.
Insecticides have shown not to be effective.
Click on the pics to view enlarged versions showing the Leaf Miner Grub in more detail