Disease of Colocasia

Phytophthora Blight of Colocasia (Taro)

Causal Organism: Phytophthora colocasiae

Symptoms

• Leaves:
  • Water-soaked lesions appear on leaf margins and expand rapidly.
  • Lesions become brown, surrounded by a yellow halo, and may coalesce, leading to leaf blight.
  • In moist conditions, whitish fungal growth is visible on the underside of lesions.
  • Leaf edges curl, and severely infected leaves collapse.
• Petioles: Black streaks or lesions on petioles. Lesions may girdle the petiole, causing wilting and breaking of leaves.
• Corms: Infection spreads to corms, leading to soft rot and foul odor. Corms become discolored, with water-soaked patches that turn brown or black.

Favorable Conditions for Disease Development

• High humidity and frequent rainfall.
• Warm temperatures (20–30°C).
• Poorly drained soils and waterlogged conditions.

Mode of Spread and Survival

• Primary Source: Soil-borne pathogen surviving in infected plant debris and corms.
• Secondary Spread: Sporangia and zoospores dispersed by rain splash, wind, and irrigation water. Contaminated planting material and farm tools also spread the pathogen.

Management

1. Cultural Practices:
   • Plant in well-drained soils and avoid waterlogging.
   • Use disease-free corms for planting.
   • Ensure proper spacing to improve air circulation and reduce humidity.
   • Rotate crops with non-host crops like cereals or legumes for 2-3 years.
   • Remove and destroy infected plant debris to reduce inoculum load.
2. Resistant Varieties: Plant resistant or tolerant varieties, if available, suited to local conditions.
3. Chemical Control:
   • Spray with Metalaxyl-M + Mancozeb (0.25%) or Copper oxychloride (0.3%) at 10-15 day intervals.
   • Soil drenching with Fosetyl-Al (0.2%) to control corm rot.
   • Fungicide application should be alternated to prevent resistance buildup.
4. Biological Control: Use Trichoderma viride or Pseudomonas fluorescens as soil amendments to suppress pathogen growth.
5. Integrated Disease Management (IDM): Combine cultural, chemical, and biological methods for effective control. Regular monitoring and removal of infected plants.