Red, purple or brown blueberry foliage can have very different meanings depending on season and pattern.
Blueberries have unusual soil needs
Blueberries prefer acidic root-zone conditions. Soil or irrigation-water chemistry that is acceptable for many landscape plants can create nutrient-availability problems for blueberries.
Check moisture and salts
Review drainage, irrigation consistency and water quality. Browning leaf edges can occur with root or salt stress.