Ripe rot

Ripe rot, caused by the fungus Coleophoma empetri, is a significant fungal disease that primarily affects American cranberry (Vaccinium macrocarpon). Known as a late-season pathogen, it leads to post-harvest and pre-harvest decay of berries, significantly impacting fruit quality and shelf life.

The causative agent belongs to the phylum Ascomycota. It survives as mycelium or as fruiting bodies (pycnidia) on infected debris and mummified berries left on the soil surface of cranberry bogs. These pycnidia release spores that are splashed onto developing fruit during rainfall, initiating the infection process.

Symptoms initially appear as small, tan to brown lesions on the surface of ripening berries. As the fungus colonizes the internal tissues, the berries become soft, water-soaked, and necrotic. Under high humidity, the fungus erupts through the skin, forming clusters of minute black pycnidia that give the rot its characteristic appearance.

The development of ripe rot is heavily dependent on microclimatic conditions. High humidity, warm temperatures, and poor air circulation within the bog canopy are critical factors. Dense vine growth and lack of proper irrigation management during the fruit development stage often exacerbate the spread of the disease.

Economic damage is caused not only by direct crop loss but also by the increased cost of sorting and processing fruit that has been infected. Integrated pest management (IPM) strategies are essential to minimize the impact of Coleophoma empetri:

• Application of registered fungicides at critical stages of plant development.
• Pruning and canopy management to improve airflow.
• Proper water management to reduce humidity levels in the bog.
• Sanitation practices, including the removal of decaying fruit to break the pathogen cycle.