Check the soil. Likely it's too dry. Blueberry roots are quite shallow. They need to be mulched to retain what moisture they receive for a while. The problem sounds like it is either that it is too dry which seems likely given the season, or that they are too wet and the roots are rotting. Did you put in lots of coarse material, stones or crocks, to ensure good drainage? I can see some on the surface but perhaps it's not great deep down in the soil. Did you recently fertilize it at all too?
Over fertilization tends to make the leaves dark green, but at the same time browning occurs on the leaf tips and leaf edges and then works its way to the center of the leaf which is why I ask.
Have a look at this site:
http://www.fruit.cornell.edu/berrytool/blueberry/leaves/BBleafbrowning.htm Might give you some pointers as to why it's browning. Although, it might also be the conditions it was kept in before purchase. Do you know the conditions it was kept in?