Do you think it could be because it is heading towards fall? Some of my deciduous plants are already showing some signs of fall colors.

I live within a few miles of one of the major commercial blueberry growers in the Eastern U.S.A. and few of the leaves in the fields seem to be turning. None of my highbush or lowbush plants have any but green leaves. If you are in zone 7 or warmer, the leaf color might be due to stress. The growers provide well drained, acid soil and water a few feet below the roots,in the sun. I have wild blueberries that seldom fruit in complete shade, with leaves still totally green. Other plants have some leaves dropping and colored but we have had a stretch of dry weather.

Do you have strongly acid soil? If not, that could be the reason your blueberries are not happy.

I don't have blueberries but my viburnum tribolum have done similar in some years (not this year yet). I always wrote it off to fall colors starting early due to stress or heat. They never seemed sick otherwise, just turned colors.

Just a thought, when my serviceberry and chokeberry bushes develop bright red leaves, it's a fungal disease. I don't grow blueberries because our soil is all wrong for them. They're my favorite food, so I wish I could have them here. Sorry, I'm not familiar with diseases that attack them.