Is it in a pot? In spring and summer I tend to keep my Blueberry bushes in full sun, in pots with the saucer beneath. Earlier in April we had heavy rain for days so one Blueberry bush is looking like your, actually worse. I think the drainage is too poor and the roots got damaged by that. I lost all the flowers, so no fruit this year from that one. I trimmed it back slightly and it was still green underneath though the branches look black and leaves starting to shrivel.

Thanks so much for your reply, had thought about that but wasn't sure if maybe it had a disease.

The obvious question is whether you have ensured they are planted in acid soil and that they are only watered with rain water not limy tap water. If that's the case, then it's probably the over watering.