By your description, it looks like White blister or leaf spot, which are fungal deseases, they can occure in wet or over-crowded conditions, in either case its best to remove affected leaves and burn them. Good Luck T bird+
Good point bookermel, I did also wonder about flea beetle too. If this is the case, the beetle is up to1/10in long and are either black and shiny or black with yellow stripes.
Young plants are especially susceptable in hot dry spells.
They can be controlled with a dusting of derris or lindane. Good Luck and thank you.