Horse Chestnut trees in the UK are currently at risk from major infections that potentially would decimate the UK population. It may be that yours has become infested, and has started to weaken as a result, hence the lack of flowering. Surveys this year show that probably around 50% of our trees are infected already.

Flowering and seeding, by the way, take an enormous amount of energy from a tree, which is why many have intermittent years of heavy flowers and crops, followed by poor years – yours may have a mixture of the two. Otherwise, our peculiar weather, last winter and spring, could have affected the flowering time, as well as inducing low pollination rates – bee populations are also in decline, and this may have affected it too (though you don’t mention whether it flowered or not).

The main issue for our Horse Chestnut trees stems from a new bacteria that is infecting them, coupled with a leaf mining moth. You may typically see browner leaves on your tree from earlier in the year too, as well as trunk wounds that appear to be weeping. The moth that is attacking them, is a leaf miner, leaving brown leaf wounds, which critically weakens them, as they are then less able to photosynthesise. Often you’ll see much of the leaf just appearing brown from these moths.

http://news.bbc.co.uk/1/hi/england/7549489.stm and here for more info on the leaf miner moth:
http://www.forestry.gov.uk/fr/INFD-68JJRC/

It’s a sad time, as these wonderful trees have been around the UK for centuries, and are fairly unique in their characteristics. I hope that yours is healthy, but keep watch for it next year, when it resprouts.

Hope this helps. Good luck! Rob

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