Diplodia stem end rot

Diplodia natalensis

Diplodia stem end rot is a disease that affects certain fruit crops, particularly stone fruits such as peaches and nectarines. It is caused by the fungus Diplodia seriata (formerly known as Botryosphaeria dothidea), and it primarily affects the stem end of the fruit. Here's an informative description of Diplodia stem end rot, including its appearance, identification, and management:

1. Appearance:

  • Symptoms on Fruit: Diplodia stem end rot typically manifests as dark, sunken lesions at the stem end of the fruit. These lesions can be firm, dry, and may extend into the fruit's flesh.
  • Concentric Rings: Lesions often display concentric rings or a target-like pattern, giving them a distinctive appearance.
  • Fungal Structures: Under certain conditions, small, black fruiting structures (pycnidia) of the Diplodia fungus may be visible on the surface of the lesions.

2. Identification:

  • Location of Symptoms: Diplodia stem end rot is characterized by its specific localization at the stem end of the fruit, distinguishing it from other fruit rots.
  • External Lesion Characteristics: The dark, sunken lesions with concentric rings are key external identifiers.
  • Internal Symptoms: Cutting open infected fruits may reveal brown discoloration and dry, corky tissue extending from the stem end into the fruit.

3. Disease Cycle:

  • Infection: The fungus enters the fruit through wounds, injuries, or natural openings.
  • Spore Production: Fungal spores are produced within the infected tissues, contributing to the spread of the disease.
  • Environmental Factors: Warm and humid conditions favor the development of Diplodia stem end rot.

4. Management:

  • Sanitation: Removal and destruction of infected fruits and plant debris can help reduce the inoculum in the orchard.
  • Pruning: Prune infected branches to improve air circulation and reduce disease pressure.
  • Fungicide Applications: Fungicides may be applied as a preventive measure, especially during periods conducive to disease development. Copper-based fungicides are commonly used.
  • Post-Harvest Practices: Implementing proper post-harvest handling practices, such as avoiding bruising or injuring fruits during harvest, transportation, and storage, can minimize the risk of infection.

5. Importance:

  • Economic Impact: Diplodia stem end rot can lead to significant economic losses in stone fruit orchards by reducing the quality and marketability of the fruits.
  • Long-Term Effects: Severe and repeated infections can impact tree health and productivity over time.