Red spots, rings, and oak-leaf patterns appear on older leaves in late June or July. Similar spots can be found on branches older than a year. The berries are pock-marked and unattractive. Some varieties may have light blotching on the fruit. Production is seriously decreased.
Powdery mildew causes similar spots, but on both sides of the leaves.
This disease appears to be spread from plant to plant by mealybugs, although other insects may be involved. It is most commonly spread, though, by planting diseased stock. Plant disease-free stock. Remove and destroy infected bushes immediately. Resistance is available for this disease.