The roots of rhododendrons growing in wet soil are attacked and rotted by water molds. Symptoms are wilting and death of the top of the plant. To diagnose the cause as root rot, examine the finer roots of plants just showing wilting. If the roots are black and soft and the outer skin easily pulls away from the inner wood, the likely cause of disease is a root rot fungus.
Plants affected by root rot show an inward curling of the leaves.
Drought alone, however, causes the same top symptoms. With root rot, a single branch near the soil surface may develop curled leaves, then die and drop its leaves. This branch dieback occurs when the root rot fungus is splashed up onto a leaf, infecting the leaf and the branch. Root rot of rhododendron is often symptomless in the landscape until stress from drought or flooding brings on disease. Fertilizers are also important in predisposing the plants to disease.