Rhododendrons are popular flowers because of their large, showy springtime blossoms. However, their beauty is significantly marred at times by leaf infections that cause spotting, wilting and early defoliation. These conditions occur for a number of reasons.
Leaf spot disease is characterised by unsightly spots or leaf loss. A disorder called leaf scorch causes evergreen leaves to turn brown during the winter or spring. Rhododendron leaves curl inward and wilt if plants are infected with Phytophthora root rot, and leaves die on specific branches because of a condition known as Botryosphaeria dieback.
Leaf spots are caused by several different types of fungus such as the Septoria species, among others. Leaf scorch occurs as a result of winter injury. The Phytophthora fungus is a soil pathogen that kills the roots of trees before progressing to the foliage. Finally, the Botryosphaeria fungus infects injured plant tissue.
Leaf spot is usually cosmetic, but use a fungicide such as copper hydroxide if the plant begins shedding leaves. Prevent winter burn by planting rhododendrons in less windy areas. Avoid root rot by planting rhododendrons in well-drained soil. No chemical treatments are available to cure infected plants. Treat Botryosphaeria dieback by pruning dying branches and avoiding rough treatment.