The time for apple harvest in Kentucky has arrived, bringing with it the possibility of less than perfect looking apples. Sooty blotch and/or flyspeck are one of many causes for blemished, ugly apples. The two fungal diseases occur together as a complex that is often called “sooty blotch/fly speck.” Sanitation, cultural practices, and fungicides all play roles in disease management.
Sooty Blotch & Flyspeck Facts
- Symptoms of sooty blotch include black-brown to olive-colored irregular blotches (Figure 1, black arrow). Fungal reproductive structures (pycnidia) may be visible in darker spots.
- Flyspeck symptoms appear as sharp, black, shiny dots grouped into clusters (Figure 1, red arrow). These black dots are fungal reproductive structures (pseudothecia).
- Sooty blotch and flyspeck may occur independently, but they usually develop together (Figure 1).
- Infection may occur during summer or throughout fall.
- Both pathogens overwinter on fallen fruit, dried fruit (mummies), and in crevices in bark and dead wood.
- Pathogens are superficial and are restricted to fruit surfaces. The flesh of the fruit is not affected.
- Sooty blotch is caused by the fungus Geastrumia polystigmatis, and flyspeck is caused by the fungus Zygophiali jamaicensis.
- Remove and discard diseased fruit to help reduce inoculum.
- At the end of the season, remove fruit from the ground, as well as cankers and dead wood that could harbor fungi.
- Homeowners and small scale growers can bag apples to prevent disease onset (ENTFACT-218).
- 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.
- Commercial growers should refer to ID-232 for fungicide recommendations.
- Apple Fruit Diseases Appearing at Harvest (PPFS-FR-T-2)
- Fruit, Orchard, and Vineyard Sanitation (PPFS-GEN-05)
- Backyard Apple Disease & Pest Management Using Cultural Practices (with Low Spray, No Spray, & Organic Options) (PPFS-FR-T-21)
- Simplified Backyard Apple Spray Guides (PPFS-FR-T-18)
- Effectiveness of Fungicides for Management of Apple Diseases (PPFS-FR-T-15)
- Commercial Fruit Pest Management Guide (ID-232)
- Bagging Apples: Alternative Pest Management for Hobbyists (ENTFACT-218)
By Kimberly Leonberger, Plant Pathology Extension Associate and Nicole Gauthier, Plant Pathology Extension Specialist