Bitter rot of fruit

The disease known as bitter rot is caused by the fungal pathogen Colletotrichum fructi. This fungus is a significant threat to orchard productivity, specifically targeting fruit tissues. It survives the winter in mummified fruit, dead twigs, and bark crevices, waiting for favorable conditions to release its spores and initiate new infections in the spring.

A wide variety of pomaceous and stone fruit crops are susceptible to this pathogen, with apples and pears being particularly vulnerable. The fungus thrives in dense canopies where air circulation is poor, which allows the spores to adhere to the fruit surface and penetrate the skin during periods of high moisture and warm temperatures.

Symptoms typically begin as small, light-colored, circular spots on the surface of the fruit. As the infection progresses, these lesions enlarge, become sunken, and eventually develop concentric rings of salmon-colored or cream-colored fungal spore masses. In advanced stages, the fruit undergoes soft rot, often leading to total decay if left untreated.

Epidemiological spread is heavily influenced by wet weather patterns. Rainfall is the primary vehicle for moving spores from infected bark or debris to healthy fruit. Once a few fruits become infected, the process accelerates rapidly during warm, humid weather, potentially leading to widespread fruit rot across an entire orchard within a short timeframe.

The economic impact of this disease is substantial, as it directly damages the marketable product. Bitter rot can significantly reduce harvest yields and compromise the storage quality of the fruit. Growers must maintain a rigorous integrated pest management strategy to minimize the presence of inoculum and prevent secondary infections.

Effective management and prevention strategies include:

• Rigorous sanitation by removing and destroying all mummified fruits and dead wood.
• Pruning trees to open the canopy, which promotes drying and reduces humidity.
• Applying protective fungicides during critical growth stages and periods of high risk.
• Maintaining optimal tree health through balanced nutrition and proper watering practices.