My sunburst cherry tree needs help.
 

hello ,I brought a mini patio orchard of 4 fruit trees.

leaves started to come out for the first time and where ok but now i have just noticed the leaves on the sunburst cherry tree are now going brown at the edges and curling.. just like Nikki 1970 as discribed in her listing ...
can anybody help me with this and tell me what it is? causing it? what can i do about it?
many thanks