Gummy stem blight

Didymella bryoniae

Symptoms:

  • Leaf Lesions: Didymella bryoniae is a fungal pathogen that causes leaf blight on cucurbit crops, including cucumbers, melons, pumpkins, and squash.
  • Circular Spots: Initial symptoms appear as small, circular lesions on the leaves.
  • Necrotic Centers: Lesions often develop necrotic centers with a tan to brown color, surrounded by a darker margin.
  • Angular Leaf Spots: As the disease progresses, lesions may coalesce, forming larger, irregularly shaped spots with an angular appearance.

2. Disease Cycle:

  • Overwintering: The fungus can survive in infected plant debris, providing a source of inoculum for the next growing season.
  • Infection: Infection occurs through spores (conidia) produced on infected debris or within pycnidia (fruiting bodies).
  • Spread: Conidia are dispersed by wind, rain, or physical contact, initiating new infections on healthy plants.
  • Favorable Conditions: Warm and humid conditions, typical of the growing season, favor disease development.

3. Host Range:

  • Cucurbit Crops: Didymella bryoniae primarily affects plants in the cucurbit family, posing a threat to economically important crops.

4. Identification:

  • Lesion Characteristics: Identification involves recognizing the circular lesions with necrotic centers and an angular shape.
  • Pycnidia: Microscopic examination may reveal pycnidia within lesions, which play a role in spore production.

5. Management:

  • Resistant Varieties: Planting cucumber and melon varieties resistant to Didymella bryoniae can help mitigate the impact of the disease.
  • Crop Rotation: Avoiding consecutive cultivation of cucurbits in the same location reduces the risk of disease recurrence.
  • Fungicide Applications: Fungicides, applied preventively or curatively, can be part of an integrated management strategy.
  • Sanitation: Proper disposal of infected plant debris minimizes the overwintering potential of the pathogen.

6. Importance:

  • Economic Impact: Leaf blight caused by Didymella bryoniae can result in reduced yields and affect the quality of cucurbit crops.
  • Global Distribution: The pathogen is widespread and can be found in cucurbit-growing regions around the world.