Is this fungal?

I believe the horse chestnut is on the list of those in danger of dying out. The leaves dying now so it doesn't produce enough conkers.

Leaf miner kill off the leaves in early summer on mine. Mine are too big to feed - but I try to pick up all the leaves in the winter to lessen leaf miner - we don't get a huge conker harvest for the size of the tree.

Years ago park keepers would clean up all the leaves. That doesnt seem to happen anymore so all the miners can overwinter in the leaf matter.