Posted: 06/07/2014 at 21:38
If there are no aphids then I suspect drought. The trees are planted very close to the fence and are therefore likely to be in a rain shadow, and the lawn is also very close to the trees and will be robbing them of the moisture and nutrients they need.
I would clear as much of a circle of bare soil around the trunks as you can - a circle with 1m diameter would be good - that way there's no competition for moisture or nutrients from the grass.
In the meantime I'd give each tree 3 buckets of water tomorrow and again on Wednesday and again the following weekend, and continue with the watering until autumn and the leaves fall.
What feeding and mulching have they had?