Is this fertilizer burn?

My blueberry bush has been developing brown edges to its leaves that slowly centralize. My raspberry bush did the same thing last year and ended up all but dying. I was told at the time it was a fungus, but sulphur made zero difference (it’s what the gardening store recommended), and it is now in a completely different pot, while skipping a ton of pots in between. I’m now wondering if it’s as simple as too much fertilizer – I don’t think I’ve ever once watered either plant hard enough for the water to run out the bottom of their fairly big pots. Any help would be appreciated.

Oh and ignore the purplish colouring of some of the leaves. That’s normal for this particular species. The brown parts are crispy and clearly dead.