Cause The fungus Pyrenobotrys compacta produces a conspicuous disease, but it appears to cause little damage. Spores in the fruiting bodies (pseudothecia) mature in early summer and infect new leaves in summer or early fall.
Symptoms Clusters or rings of discrete black fruiting bodies appear on the lower leaf surface in late winter or early spring. Purplish red lesions with diffuse margins are seen on the upper leaf surface above the fruiting bodies. Leaf lesions turn brown, and a few leaves yellow and fall from the upright by early summer. Symptoms are only on the previous season's growth.
Chemical control Fungicides applied to control fruit rots also control this disease.
Reference Polashock, J.J., Caruso, F.L., Averill, A.L., and Schilder, A.C. 2017. Compendium of Blueberry, Cranberry and Lingonberry Diseases and Pests. Second edition. St. Paul, MN: APS Press.