The season for apple harvest has arrived, bringing with it the possibility of late season fruit rots (summer rots). While fruit rots have a variety of causes, the most common fungal fruit rot of apple in Kentucky is bitter rot. This disease results in rotten, inedible fruit. Fungicides are available for management; however, sanitation is critical for disease prevention. Ongoing research at the University of Kentucky is providing new insights and understanding of the pathogens that cause bitter rot.
Bitter Rot Facts
- Symptoms include small, slightly sunken lesions that 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 become visible.
- Initial infection begins as early as bloom and may continue through harvest.
- The pathogen overwinters in fallen fruit, dried fruit (mummies), and in crevices in bark and dead wood.
- Caused by multiple species of the fungus Colletotrichum.
- Remove and discard diseased fruit immediately.
- At the end of the season, remove fruit from the ground, as well as cankers and dead wood that could 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.
- Five species of Colletotrichum have been documented as causal agents of bitter rot in Kentucky.
- More than one species has been documented within the same orchard and within a single tree.
- Aggressiveness and fungicide sensitivity varies across species.
- Continued research is needed to provide growers with more targeted management recommendations.
- Samples of bitter rot are needed to continue with this research. Please contact Dr. Nicole Ward Gauthier (email@example.com) for more information.
- Apple Fruit Diseases Appearing at Harvest (PPFS-FR-T-02)
- Fruit, Orchard, and Vineyard Sanitation (PPFS-GEN-05)
- Simplified Backyard Apple Spray Guides (PPFS-FR-T-18)
- Effectiveness of Fungicides for Management of Apple Diseases (PPFS-FR-T-15)
- Midwest Commercial Tree Fruit Spray Guide (ID-92)
- Characterization of Colletotrichum species causing bitter rot of apples in Kentucky orchards (M.S. Thesis by Misbakhul Munir)
By Kimberly Leonberger, Extension Associate, and Nicole Ward Gauthier, Extension Plant Pathologist