My blueberries... some of them are showing similar issues. I'm clueless, so can't wait to hear from an expert. Try giving it a dose of epsom salt. The chlorosis at the edge of the leaf where the brown starts leads me to believe that it was an issue caused by sudden lack of nutrient uptake. Perhaps the plant went a bit dry for just a tad too long. Or it needs a bit of fertilizer. Got any slow release? If not, try some weakly mixed miracle grow.