Hosts:  Aspen and cottonwood

Symptoms/signs:  Ciborinia whetzelii forms brown to black spots, or stromata, in blighted leaves. Infected leaves turn brown and the ink spots, or sclerotia, begin to drop out leaving a circular hole in the dead leaves.

Biology:  Ciborinia whetzelii infects young leaves in the spring by ascospores produced on fruiting structures that overwintered on fallen leaves. Infected leaves begin to die midsummer, but defoliation may not take place until autumn.

Effects:  Ink spot leaf blight is more severe on smaller aspen trees and in the lower crowns of larger trees. As with many aspen diseases, some clones appear to be more susceptible than others.

Similar Insects and Diseases:  This fungus may be confused with Marssonina populi; however, C. whetzelii produces well-defined circular and slightly raised fruiting structures, while those of M. populi are irregularly shaped and flattened.

Reference:  38