Dr. John Braswell brought me some sample of Exobasidium vaccinii on Friday. This is a disease that, frankly, not much is known. Questions remain on its life cycle and how to effectively control it. In some blueberry growing areas it is a serious problem, but in others just a minor issue. A very good write-up on this disease is at the following link:
Small Fruit News http://www.smallfruits.org/Newsletter/Vol11-Issue4.pdf This article also has some preliminary control recommendations.
So, what are the symptoms of the disease? Leaf spots that may appear sunken on the upper side of the leaf are one sign, as well as very white round rather large spots on the underside of the leaf.
Older infections turn brown.
The fruit displays mixed color and green areas. The green areas will not properly ripen. It may be an issue when sorting the fruit because the green portion tends to be heavier and may gravitate toward the bottom, thus being hidden from view.
The disease is more prevalent in areas with high humidity and poor air movement, so proper site selection is crucial for reducing this disease. Proper pruning strategies to increase air flow may also help.