Alterneria cucumerina

Fungal Disease

Alterneria cucumerina

Fungal Disease

Introduction

Cucurbit Alternaria Leaf Blight is a fungal disease caused by Alternaria cucumerina. It affects cucurbits such as watermelon, cantaloupe, cucumber, zucchini, pumpkin, and winter squashes, reducing yield and fruit quality.

Symptoms

• Leaf Lesions:
  • Brown spots with concentric, target-like rings.
  • Yellow halos around the lesions.
• Fruit Symptoms:
  • Sunken brown spots that may turn dark and fuzzy due to sporulation.
  • Sunscald due to leaf loss.

Disease Cycle & Spread

• Primary Source of Infection:
  • Survives as mycelia in infected soil-bound plant debris for up to two years.
• Mode of Spread:
  • Windborne spores (conidia).
  • Splashing water, workers, equipment, and insects.
  • Infected seeds can also carry the pathogen.
• Infection Process:
  • When temperatures rise and leaf wetness increases, mycelia produce spores (conidia) that infect healthy plants.
  • The cycle repeats as new conidia form on infected leaves.

Favorable Conditions for Infection

• Temperature:
  • Optimal range: 21–32°C (70–90°F).
  • Spores can germinate between 10–35°C.
• Humidity:
  • High humidity promotes infection.
  • Frequent rains increase relative humidity, aiding disease spread.
• Other Factors:
  • Prolonged leaf wetness increases disease severity.
  • Poor plant nutrition, especially low nitrogen, weakens plant defenses.

Management Strategies

• Cultural Practices:
  • Crop rotation: Avoid planting cucurbits in the same area for consecutive years.
  • Field spacing: Increase distance between cucurbit fields to reduce spore spread.
  • Avoid overhead irrigation to minimize leaf wetness.
  • Destroy or till under infected crop debris after harvest.
• Chemical Control:
  • Timely fungicide applications can slow disease progression.

Conclusion

Cucurbit Alternaria Leaf Blight can significantly impact yield and fruit quality. Implementing preventive cultural practices along with strategic fungicide use can help manage this disease effectively.