Problem: Phytophthora Root Rot (Avocado)
This plant disease is caused by a soil-inhabiting fungus (Phytophthora cinnamomi) that infects many fruit, nut, and ornamental trees and shrubs. It penetrates the roots and crown of the tree. As the fungus decays the sapwood, the flow of water and nutrients is blocked, eventually resulting in the death of the tree. The fungus is spread by infected plants and by infested soil and soil water. Phytophthora root rot is greatly favored by wet or poorly drained soil. Trees planted in lawns, flower beds, or other moist or poorly drained areas are highly susceptible to this fungus.
Once the fungus becomes established in the soil, it will remain indefinitely. To prolog the lives of mildly infected trees, remove the soil from around the crown of the tree, exposing the major roots. Always keep this area dry by providing drainage away from the tree. Avoid overwatering. Remove severely diseased and dying trees. Do not replant susceptible plants in the same area.