We have 3 older high bush blueberries, and over the past few years, they’ve been producing less and less. The leaves have looked oddly red, especially in fall. This year, the middle one was dead, and the two on the sides are nearly blossomless and oddly colored. Most of the branches are dead at the tips - 4” or so. A lowbush blueberry right by them is normal, green, and had lots of flowers. (Last picture) Could this be scorch?
Lane County Oregon blueberries
Yellowing leaves suggest your blueberry is suffering from chlorosis. In these plants, this is commonly because of nutrient deficiency; it sounds as if your blueberry is lacking in iron. This tends to happen because the soil pH is too high, at which point the blueberry can no longer take up iron available in the soil. Plants need iron to form chlorophyll, which is used in photosynthesis. To remedy the problem, use iron chelate, either as a foliar feed or added to the soil. This is a short-term solution that works by reversing the deficiency in the soil.
Blueberries need a soil pH of 5.5 or lower to thrive. It seems strange that your soil is not acidic enough with all you’ve been doing, but it may have got out of kilter. You could buy a soil pH meter to find out what is happening. If the soil is not acidic enough, the quickest solution is to use sulphur chips to lower the pH.
It's also always a good practice to prune dead or dying branches off your blueberry bushes every winter. This way your plant has the best chance to photosynthesize properly and won't develop fungal diseases if there isn't proper air circulation.