Apple Bitter Rot Season is Upon Us

While fruit rots have a variety of causes, the most common fungal fruit rot of apple in Kentucky is bitter rot. The disease results in rotten, inedible fruit. Fungicides are available for management; however, sanitation is critical for disease prevention.

Bitter Rot Facts

  • Symptoms begin as small, slightly sunken lesions that enlarge and eventually develop a bull’s-eye pattern (Figure 1). Cutting into infected fruit reveals an internal rot with a V-shaped pattern (Figure 2).
  • Symptoms may not appear immediately after infection and may take several months to develop.
  • Initial infection begins as early as bloom and may continue through harvest.
  • The fungal pathogen overwinters in fallen fruit, dried fruit (mummies), and in crevices in bark and dead wood.
  • Bitter rot is caused by multiple species of the fungus Colletotrichum.

Figure 1:   Sunken lesions with bull’s-eye appearance are common symptoms of bitter rot on apple. (Photo: Nicole Gauthier, UK)

Figure 2: Internal V-shaped rot in apple caused by bitter rot. (Photo: Nicole Gauthier, UK)

Management Options

  • Remove and discard diseased fruit immediately.
  • At the end of the season, remove fallen fruit from the ground and prune out cankers and dead wood that may harbor fungi.
  • Plant cultivars that are less susceptible to bitter rot, including ‘Rome Beauty,’ ‘Winesap,’ and ‘Red’ or ‘Yellow Delicious.’
  • Homeowners can apply fungicides that contain captan or mancozeb beginning soon after petal fall and continuing every 10 to 14 days until harvest. Always follow label directions when utilizing fungicides.

Additional Information

  • Apple Fruit Diseases Appearing at Harvest (PPFS-FR-T-2)
  • Fruit, Orchard, and Vineyard Sanitation (PPFS-GEN-05)
  • Simplified Backyard Apple Spray Guides (PPFS-FR-T-18)
  • Backyard Apple Disease & Pest Management Using Cultural Practices (with Low Spray, No Spray, & Organic Options) (PPFS-FR-T-21)
  • IPM Scouting Guide for Common Problems of Apple (ID-219)
  • Scouting Guide for Problems of Apple Mobile Website (Apple Scout)
  • Effectiveness of Fungicides for Management of Apple Diseases (PPFS-FR-T-15)
  • Midwest Fruit Pest Management Guide (ID-232)
  • Characterization of Colletotrichum species causing bitter rot of apples in Kentucky orchards (Thesis by Misbakhul Munir)

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By Kimberly Leonberger, Plant Pathology Extension Associate, and Nicole Gauthier, Plant Pathology Extension Specialist

Posted in Fruit
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