Blueberry plants fungus

sternus1 says...
your blueberry has outgrown its pot, and the potting mixture also needs to be changed. Mix 50% premium potting mix with 50% pine chips. To this, add sand and sphagnum moss until the mixture is totally free draining. Don't use coir; I don't know why they don't liek it, but they don't. If you're watering its leaves with mains water, stop doing that--they hate it, and you can only water blueberry leaves with either rainwater of filtered water. Your soil mixture is also far too dry; whilst blueberries don't like to be sitting in water, they hate dry soil even more.

I'm not convinced the spottyness is owing to a fungus, because it if was, the mancozeb would have cleared it up. It's a sure thing. What's more likely is that its being caused by a PH problem or nutrient deficiency or excess.

If it were mine, I'd cut off the worst affected areas, repot in a container at least twice as large, fill to capacity with the soil mixture I mentioned (you can use azalea mix too, but I have doubts about this tbh) and then on top of this, plant on a mound, filling over the roots with more soil mixture followed by a fine mulch (the cheapo brunnings brand potting mix is excellent for this task, and is highly acid--which blueberries love). Then water it in with seasol, also give it a seasol foliar spray. Fetilise with fruit and citrus or rose fertiliser after a fortnight at least. Don't overuse this as you're blueberry will outgrow the pot again.