Friday, 6 September 2013

The state of our conkers

Earlier in the summer I commented that the horse-chestnut trees in my area weren't too badly affected affected by the leaf-miner. What is the situation now?
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.
I still suspect that the exceptionally late spring could have caused this effect - by affecting the first generation of the leaf-miner moth, it would have had a knock on effect on the second generation. Maybe, the very local variations in shelter and warmth of trees earlier in the spring was sufficient to cause this variation? In previous years it is possible that there were so many moths anyway, despite local variations, that they quickly reached a 'saturation point' on all trees.
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.


  1. Although I have no hard evidence to corroborate your story, I do remember thinking a couple of times this year that the state of the trees didn't appear to be consistent.

    Last year, walking past trees on my normal dog walking route, they all appeared to be pretty much the same. This year I'm sure there were variations and also within a few hundred metres, as you say. I think it was the close proximity that made me notice.

    It's only until I read this post that I now realise it "wasn't just me" ;)

  2. Here are a few comments from people who have emailed Conker Tree Science in the past few days. These show that I'm not alone in my impression of damage to the horse-chestnut trees.

    "We've certainly found that our horse chestnut has been less affected by the moth this year. It seems to have fewer brown patches and the leaves are still quite green in comparison to last summer."

    "This year our chestnut tree is in much better shape. Leaves are damaged but mostly green."

    Trees "are considerably less affected than before. In fact until three weeks ago it seemed they had shaken off the little beggars, with conkers nearly back to pre-infestation levels."

    However, one person commented that "About 7 years ago the leaf miner hit the local horse-chestnut trees and each year it has been getting progressively worse. This year I would estimate a rating at a level of 3 to 4 and is certainly the worst so far."

  3. I also have been noticing the poor state of leaves on the Horse Chestnut and believe it affects the trees that have white blossom in April more than it affects the purple blossom. Has any research been given to this theory. I have several purple blossom trees that I monitor each year in my locality and they all seem to be less affected than the white blossom trees