Ripe Fruit Rot

Ripe fruit rot caused by Monilinia or Botrytis results in firm, circular spots that spread rapidly over fruit. Monilinia causes dark brown lesions on fruit that eventually turn black from the development of pseudosclerotia (fungal tissue), whereas Botrytis causes light tan to grayish lesions with gray spores. Spore masses may grow on the rotted areas. Fruit becomes more susceptible as it ripens. Botrytis-diseased fruit usually do not remain on the tree until next season, but they are present as inoculum sources for the current season's crop. When Monilinia-diseased fruit remain on the tree, they are known as mummies.

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 can infect uninjured ripening fruit and cause green fruit rot and incipient infections of young fruit. Wetness, either rain or dew, and injury or fruit cracking increases preharvest infection and subsequent rot. Rhizopus spp. invades only ripe fruit that have been injured and the decay is a postharvest concern only.

Fruit rot is managed by controlling blossom and twig blight in spring, removing blighted twigs when possible, using appropriate levels of nitrogen fertilizer and water, removing or turning under thinned fruit, controlling fruit-feeding insects such as peach twig borer and oriental fruit moth, and making preharvest treatments when necessary. Early maturing cultivars typically have little trouble with ripe fruit rot.

Take fruit samples every other week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard and a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program, see FRUIT EVALUATION AT HARVEST. Record results (PDF) for harvest sample.

Treatments of sulfur dust are acceptable for use in an organically certified crop.

Fungicides are preventive, not eradicative; they must be applied to uninjured fruit before infections occur. Injured fruit cannot be protected from Monilinia or Botrytis rot by preharvest sprays. Preharvest sprays for Monilinia should be applied as needed during the last 4 weeks before harvest. Where Rhizopus fruit rot is a problem, treat 10 days to 1 day before harvest. After harvest, Rhizopus can be controlled by storing the crop at temperatures below 40°F.

• Fruit sampling for pest damage in harvest (PDF)