The genus hydrangea consists of several flowering plants that are susceptible to a variety of plant diseases. Leaf diseases of hydrangeas can cause defoliation and aesthetic damage. Early identification and control are vital for treating these leaf diseases.
Hydrangeas are susceptible to three leaf diseases: powdery mildew, cercospora leaf spot and anthracnose. Powdery mildew and cercospora leaf spot are aesthetic diseases that rarely cause extensive plant damage, whereas anthracnose can cause defoliation. Humidity and warm weather conditions are favourable for cercospora and anthracnose. Powdery mildew favours dry, low light conditions.
Powdery mildew appears as a white powder with ruffled edges on the upper surface of leaves. Severe infections cause leaf wilt and death. Symptoms of cercospora leaf spot consist of large, dark fungal spots on leaf surfaces. Severe infections can cause defoliation but typically causes aesthetic damage, reports the University of Arkansas Division of Agriculture. Irregularly shaped brown spots on leaf and blossom surfaces with localised tissue death identify an anthracnose infection.
Powdery mildew infection control consists of physically removing the fungus from leaf tissue and destroying infected and fallen leaves. The Alabama Cooperative Extension System recommends fungicidal control for cercospora and anthracnose infections when symptoms first appear.