Root rot is caused by the fungi Phytophthora nicotianae and P. cinnamomi. Leaves turn from normal dark green to light green as the plant declines. Roots are dark and rotted. The bark rots and peels at the crown. Death of the entire plant is characteristic of this disease.
Prevention & Treatment: Root rot is favored by high soil moisture and warm soil temperatures. The disease is more severe in heavy clays or poorly drained soils. Over-watering plants or long periods of heavy rain also favor disease development. Phytophthora root rot must be prevented, as chemicals are often ineffective in controlling this disease after above-ground symptoms become obvious.

The following suggestions may aid in the prevention of root rot:
• Purchase disease-free plants from a reputable nursery.
• In areas where plants susceptible to root rot have died, replant with plants that are not susceptible.
• Plant root rot-susceptible plants in well-drained areas or in raised beds. If the soil is heavy clay, mix it with a porous material such as bark.
• The soil around infected plants may be treated with the appropriate fungicide according to the directions on the label. This may reduce the spread of the fungus among plants, but these chemicals may not kill the fungus in infected plants. Read and follow all directions on the fungicide label.