Well, my impression is that the leaf-miner damage is a lot more variable than in previous years. By this time of year I would have expected almost all the horse-chestnut trees to have completely brown leaves that were curled up and dry (especially at the base of the crown of the tree). Instead some trees are badly affected (though maybe not as much as previous years?) while other trees are much more lightly affected.
|A badly affected tree (complete with conkers) in my village. I think the trees were even more badly affected by the leaf miner last year. From research published last year, those conkers will be smaller than they used to be, thanks to the effect of the leaf miner.|
|This tree, just a couple of hundred meters up the road, is much less badly affected. Last year in was affected much more badly by the leaf mine.|
That's just a theory, and the fact that every year is different is part of what makes ecological science fun. But it also makes it really difficult to make precise predictions about the future!
For now though, I'm enjoying horse-chestnut trees with some green left in their leaves - something I haven't seen in September for many years.