Bitter rot of apple

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Bitter rot lesion

Bitter rot of apple is a fungal disease that affects apple trees, causing significant damage to the fruit. The disease is caused by fungi in the genus Colletotrichum, primarily Colletotrichum gloeosporioides and Colletotrichum acutatum. Bitter rot is characterized by sunken, dark lesions on the fruit, which can lead to extensive crop loss if not managed properly.

Symptoms

The primary symptom of bitter rot is the appearance of small, circular, sunken lesions on the surface of the apple. These lesions are initially light brown but darken over time, often developing a concentric ring pattern. As the disease progresses, the lesions enlarge and may become covered with pinkish spore masses. Infected fruit may also exhibit a bitter taste, hence the name "bitter rot."

Disease Cycle

Bitter rot fungi overwinter in mummified fruit, dead wood, and cankers on the tree. In the spring and summer, spores are produced and spread by rain, wind, and insects. Infection typically occurs during warm, wet weather, with optimal conditions being temperatures between 25-30°C (77-86°F) and high humidity. The spores germinate on the fruit surface, penetrate the skin, and begin to develop the characteristic lesions.

Management

Effective management of bitter rot involves a combination of cultural practices and chemical controls. Key strategies include:

• **Sanitation**: Remove and destroy mummified fruit, pruned wood, and other debris that can harbor the fungus.
• **Pruning**: Proper pruning to improve air circulation and reduce humidity within the tree canopy.
• **Chemical Control**: Application of fungicides during the growing season, particularly during periods of warm, wet weather. Commonly used fungicides include captan, thiophanate-methyl, and strobilurins.

Related Diseases

Bitter rot can be confused with other apple diseases such as black rot, white rot, and apple scab. Each of these diseases has distinct symptoms and management practices, making accurate diagnosis important for effective control.

See Also

• Apple scab
• Black rot
• White rot
• Colletotrichum