Make pruning cuts several inches below the discolored wood. Regular watering and good soil fertility will improve plant health and reduce the risk of Phomopsis dieback. Also, apply fungicides as recommended for controlling leaf spot diseases. Phytophthora Root Rot Root rot, caused by the fungi, Phytophthora cinnamoni , P. parasitica , and P. citricola , is a devastating disease of evergreen azaleas. Kurume-type azaleas and most rhododendron cultivars are very susceptible to root rot.
Conditions favoring root rot development are water-logged soils and warm soil temperatures.
Deep planting, overwatering, and heavy rains also favor disease development. Infected roots are reddish-brown and brittle. At early stages of root rot, some yellowing of the leaves and slowed plant growth may be observed. Early root rot symptoms could easily be confused with the symptomsof a nutritional deficiency or drought stress. Severe damage to the root system greatly reduces plant vigor and often results in plant death.