Blueberries are native to North America, and there is a blueberry type for every climate: lowbush, which do well in Northern climates; highbush, which are the most common types of blueberries found in home gardens; rabbiteye, which are suited for warmer climates; and hybrid combinations. Once blueberries are established, the plants need little attention. Although the fruit is relatively trouble-free, occasionally the leaves will turn yellow or pale green, indicating a problem with the plant--either a nutrient deficiency, a virus or a fungal infection.
Nutrient deficiencies present on blueberry leaves in a number of ways. Yellow leaves with green veins indicate lime-induced chlorosis from alkaline soil, which prevents the plant from taking up enough magnesium or iron, according to "Grow Fruit" by Alan Buckingham. A magnesium deficiency will also cause irregular pale green and yellow markings on leaves. A potassium deficiency can turn green leaves brown. Nitrogen deficiencies cause the leaves to turn a pale green.
Viruses can also attack blueberries, causing leaves to turn color. Blueberry stunt, which is caused by a phytoplasma, causes the leaves to turn yellow between the veins and along the edges, and later turn red earlier than the rest of the plant, according to the University of Connecticut Integrated Pest Management. Blueberry virus causes yellow-green mottling on leaves as well as new shoot dieback and failure to thrive throughout the plant, including the fruit.
Fungus infections, such as stem blight, can also cause blueberry leaves to turn yellow. This fungus first causes the branches to die back, turning the leaves yellow and brown as they die, according to North Carolina State University. Fungal leaf spot can also affect blueberries, first causing spots to form on the leaves and then turning the leaves yellow before they fall off. Phytophthora root rot is another fungus disease that causes blueberry leaves to turn yellow. The disease first attacks the roots of the plant and then leaves, turning them yellow in the midsummer.