Azalea lace bugs cause this yellow, stippling action on the leaves due to their feeding on leaf undersides. Observe on the back of the leaves tiny black, tar-like droplets, of insect excrement- another indicator of lace bugs. Control is probably needed: Spray the backside of the leaves with a horticultural oil.

 Warning: the yellow stippling marks on the leaves don't go away anytime soon. They will remain until next spring when new growth appears. Yellow spots indicate past damage. This is why you need to look for the insects to make sure they are still there and your spray will be effective. The insect is 1/4" and easy to spot. They will be on the bottom of the leaves. 
good link:
http://www.clemson.edu/extension/hgic/pests/plant_pests/shrubs/hgic2051.html