Ripe Fruit Rot

Fruit rot caused by Monilinia or Botrytis species results in dark brown, firm, circular spots that spread rapidly over fruit. Tan spore masses may grow on the rotted areas. The fruit become more susceptible as they ripen. Diseased fruits usually do not remain on the tree until the next season, but are present as inoculum sources for the current season's crop.

Rhizopus rot is a postharvest storage problem. The decaying fruit tissue is watery and soft; the fungus is identified by masses of white mycelium with tiny black sporangia that form most abundantly on fruit near the edge of containers.

Monilinia and Botrytis species can infect uninjured ripening fruit. Moisture, either rain or dew, and injury or fruit cracking increases the probability of preharvest infection and consequent rot. Rhizopus invades ripe fruit that has been injured or cracked, causing the fruit to rot after harvest.

Injured, split fruits cannot be protected from rots caused by Monilinia and Botrytis by preharvest sprays, but uninjured fruit can. The best fungicide to use for control depends on whether Botrytis is present alone, Monilinia alone, or both are present. Since it is not practical to try to distinguish the species present, the best treatment materials tend to be those that effectively control both species.

Protect ripe fruit from Rhizopus either with a preharvest treatment (for fruit that will be sold right after harvest) or a postharvest treatment (for fruit that will be shipped). After harvest, Rhizopus can be controlled if the fruit is stored below temperatures of 40°F. Apply a preharvest treatment 1 to 14 days before harvest. A postharvest spray can be made during stem cutting and sizing operations.