The genus viburnum consists of a variety of shrubs and small trees. Wrinkled leaves of viburnum are an aesthetic and vigour problem caused by various fungal pathogens. Early identification and control are important for treating diseases that cause wrinkled leaves.
Two major diseases of viburnum cause wrinkled leaves, downy mildew and powdery mildew. Downy mildew fungus, caused by Plasmopara viburni, is a leaf disease of viburnum that can cause wrinkled leaves. The fungus favours excess moisture on the upper side of leaf tissue for infection. Powdery mildew, caused by numerous fungal pathogens, is a leaf disease of viburnum. The disease spreads by wind and overwinters in leaves.
Identification of downy mildew consists of light green leaf spots, grey fungal growth on leaf surface, wrinkled leaves from leaf browning and leaf death. Identification of powdery mildew infections consist of distorted leaf growth, wrinkled leaves, white powdery spots and leaf death. The fungus can cause distorted leaf growth of new foliage, which can appear as wrinkled leaves.
Fungicidal spray and pruning long branches to improve air circulation are effective methods for controlling downy mildew, according to the Clemson University Cooperative Extension. Control for powdery mildew infections consist of physically removing fungal build-up from leaf surfaces, destroying fallen infected leaves and using fungicidal spray.