Covering the crowned beds with black plastic or similar material along with a thick layer of gravel or oyster shells will greatly reduce the spread of Phytophthora . The drainage system should be designed to stop runoff water from flooding container areas. Plantings of azalea and rhododendron in nurseries and landscapes should also be established on crowned, raised beds. Incorporate pine bark or a similar coarse organic amendment to a depth of 8 to 12 inches to improve drainage. Flat planting of azaleas, rhododendrons, and other root rot-susceptible ornamentals is not recommended, particularly in poorly drained soils.
Stress caused by overwatering or lack of water can lead to increased root rot disease.
Group plants by container size and water needs to prevent overwatering. Be careful not to overwater container-grown deciduous trees and shrubs during the winter and early spring, particularly in areas likely to get heavy winter rains. Also, take daily rainfall into account when scheduling irrigation. Phytophthora root rot fungi have been found in ponds receiving runoff from production beds. To reduce the chances of contamination of liner or container stock with root rot fungi, use either chlorinated, deep well, or quality surface water from a clean pond or stream.