Diseases of Azalea

Abstract

Florist azaleas (Rhododendron obtusum (Lindl.) Planch) are grown worldwide in greenhouses as a potted flower plant. They belong to the evergreen group but vary in their cold hardiness, so they must be protected against cold winter conditions. Many cultivars have been developed based largely on their horticultural traits, especially flower size and color. Some cultivars are prone to develop witches’ broom, thought to be a genetic disorder. However, most florist azaleas are susceptible to a number of diseases, but little attention has been paid to their resistance/susceptibility through breeding. Of concern to growers are diseases caused by species of Cylindrocladium, Pythium, Phytophthora, Rhizoctonia, and occasionally Exobasidium. Many of the diseases of florist azaleas, such as infections caused by Cylindrocladium, occur during the propagation phase of rooting cuttings, with surviving, infected-but-symptomless plants later succumbing to the disease.