Cherry tree problem

My sons Cherrry tree in his garden is looking poorly, with the growing tips going brown .
First thoughts were not enough water but we've had weeks of rain !
Any thoughts about what could be wrong

 

Could it be aphids, they often collect under the leaves, the leaves roll up and eventually die.

 

@martyn bromley Have a look here and see what you think …
Blossom wilt / RHS Gardening