Rhododendrons, valued for their flowers and evergreen leaves, are susceptible to diseases and other problems that cause dead and yellow leaves. Early identification and treatment are vital for revitalising rhododendrons with dead and yellow leaves.
Cercospora Leaf Spot
Cercospora leaf spot, caused by the fungus Cercospora handelii, is a disease of rhododendrons that causes leaf death and yellowing. Symptoms consist of brown spots, tan spots with yellow halos and eventual leaf death, according to The Pennsylvania State University Department of Plant Pathology.
Nutrient deficiency of rhododendrons, as well as other plants, can cause leaf death and yellowing. Yellow foliage is a symptom of low fertility, iron deficiency or an imbalanced pH level, according to the Cornell University Cooperative Extension. An imbalance of nutrient levels or pH levels can cause leaf death if not controlled.
Control for Cercospora leaf spot consists of destroying fallen infected leaves and using fungicidal spray, according to The Pennsylvania State University Department of Plant Pathology. Control nutrient deficiency through systemic fertiliser application, applying an iron sulphate solution or balancing the soil's pH, according to Cornell University Cooperative Extension. University-based or private labs can test soil for nutrient and pH levels.