Agriculture: Avocado Pest Management Guidelines

Phytophthora Fruit Rot

  • Phytophthora mengei (P. citricola)
  • Symptoms and Signs

    (View photos to identify causes of fruit damage)

    Diseased fruit have a distinct circular black area that usually occurs near the bottom portion or lowest spot on the fruit. Internally, the rot extends into the flesh, darkening it in the same pattern as on the affected surface. Affected fruit are often touching the soil or are hanging on low branches. Most damage occurs within 3 feet of the ground.

    Comments on the Disease

    Phytophthora fruit rot is caused by Phytophthora spp., usually P. mengei, the same fungus that causes Phytophthora trunk canker and crown rot. Phytophthora fruit rot is usually of minor importance in California. Most damage occurs after prolonged wet conditions, the same situation that favors anthracnose. In contrast to anthracnose, which is primarily a postharvest problem, Phytophthora fruit rot infections often become obvious while fruit is still hanging on the tree, as well as causing decay after harvest.

    Management

    The most common cause of infection is likely the splashing of Phytophthora propagules from the soil surface to the fruit during heavy rain or sprinkler irrigation.

    • Prune lower limbs so they are 2 to 3 feet from the ground.
    • Maintain a thick layer of mulch to hasten decomposition of the pathogen in soil.
    • Consider removing and disposing of old fruit or fruit lying on the ground because the fungus sporulates on dropped fruit.

    Prune out dead limbs and twigs, and dispose chip large pieces of dead wood. Move and old fruitwood away from avocado trees.

    Text Updated: 09/16