Leaf Spot of Strawberry

Causal Organism:

• Mycosphaerella fragariae
• Sub-division: Ascomycotina

Symptoms:

• Affected Parts: Leaves, fruits, berry caps, petioles, and runners.
• On Leaves:
  • Small, round, necrotic (dead) spots appear on leaves.
  • Spots resemble bird’s-eye spots.
  • Spots eventually develop white centers with distinct reddish-purple to brown borders.

Etiology:

• Causal Agent: Mycosphaerella fragariae is an ascomycete fungus.
• Mode of Infection:
  • The fungus infects leaves and other above-ground parts through windblown conidia.
  • The pathogen survives on infected plant debris, which serves as a source of primary inoculum.

Disease Cycle:

• Primary Infection:
  • Ascospore is the primary inoculum.
  • Ascospores are released from pseudothecia on old infected leaves.
• Secondary Infection:
  • Windblown Conidia serve as the secondary inoculum.
  • Conidia are produced on leaf spots and spread to healthy plant parts by wind and rain splashes.

Favorable Conditions:

• Warm and humid weather favors disease development.
• Prolonged leaf wetness increases the severity of the disease.

Management:

1. Cultural Practices:
   • Use of Disease-free Plants: Start with healthy, certified disease-free transplants.
   • Sanitation: Remove and destroy infected leaves and plant debris to reduce inoculum levels.
   • Proper Spacing: Ensure proper plant spacing to improve air circulation and reduce leaf wetness.
2. Resistant Cultivars: Plant resistant strawberry varieties to reduce disease incidence.
3. Chemical Control:
   • Copper Oxychloride Spray:
     • Apply at 0.3% concentration.
     • Begin applications early in the season and repeat as needed, especially during humid conditions.
4. Soil Fumigation:
   • Effective for managing soil-borne inoculum.
   • Helps reduce the carryover of the pathogen between planting seasons.