Blast Disease in Paddy
धान में ब्लास्ट रोग — Identification, Control & Prevention
Blast Disease in Paddy | धान में ब्लास्ट रोग
Blast (Magnaporthe oryzae) is the most destructive disease of paddy worldwide, and a major yield threat in India's Kharif season. In severe outbreaks, neck blast can cause 40–70% yield loss in susceptible varieties. Early identification and timely fungicide application are critical.
Types of Blast / ब्लास्ट के प्रकार
1. Leaf Blast / पत्ती ब्लास्ट
Diamond-shaped lesions with grey centers and brown borders on leaves. Initially small olive-green water-soaked spots, rapidly expanding to characteristic spindle shapes with pointed ends. Appears from nursery stage to tillering.
2. Neck Blast / गर्दन ब्लास्ट (Panicle Blast)
Infection at the neck of the panicle — the most damaging form. Infected neck turns brown-black; panicle either does not emerge fully or falls over (white ear). Heavy yield loss.
3. Node Blast / गांठ ब्लास्ट
Dark brown to blackish lesions on nodes, causing culm breakage. Common in high-nitrogen fields.
Conditions Favoring Blast / ब्लास्ट के लिए अनुकूल परिस्थितियाँ
- High humidity (> 90%) with nighttime temperatures of 17–22°C
- Prolonged leaf wetness (dew)
- Excess nitrogen application
- Sandy soils with poor silicon status
- Susceptible varieties (most HYB and some popular HYV varieties)
Identification / पहचान
| Stage | Symptom | Action |
|---|---|---|
| Nursery (7–20 DAS) | Diamond-shaped lesions on seedling leaves | Emergency fungicide spray |
| Tillering (21–50 DAS) | Multiple leaf lesions, coalescence | Spray + check N rate |
| Panicle initiation (PI) | Lesions on flag leaf, leaf sheath | Preventive spray at PI stage — critical |
| Heading (50–70% panicle emergence) | Brown-black neck lesion | Emergency spray within 24–48 hours |
Management / प्रबंधन
Fungicide Recommendations / फफूंदनाशक
| Fungicide | Dose / Acre | Best for |
|---|---|---|
| Tricyclazole 75% WP | 120 g/acre | Leaf blast and neck blast (preventive + curative) |
| Isoprothiolane 40% EC | 300 ml/acre | Neck blast at heading — systemic, moves into panicle |
| Azoxystrobin 23% SC | 200 ml/acre | Leaf blast — good residual activity |
| Propiconazole 25% EC | 200 ml/acre | Combined blast + sheath blight — good tank mix option |
| Kasugamycin 3% SL | 600 ml/acre | Leaf blast in nursery — antibiotic mode, rotational use |
Spray Schedule / छिड़काव कार्यक्रम
- First spray: At panicle initiation (PI) stage — even if no symptoms visible — with Isoprothiolane 40% EC @ 300 ml/acre OR Tricyclazole @ 120 g/acre. This one spray prevents neck blast and saves the panicle.
- Second spray: At 50% heading — repeat Isoprothiolane or Tricyclazole if conditions remain conducive (humidity > 85%, nighttime temperature below 22°C)
- Leaf blast (tillering): Spray Tricyclazole or Azoxystrobin when diamond-shaped lesions appear on 5%+ leaf area
Do not delay neck blast spray: Once the neck turns black, yield cannot be recovered. The preventive spray at PI is the single most important input in blast-prone areas.
Prevention / रोकथाम
- Use blast-resistant varieties where available (IR 64 type, DRRH 3, varieties with Pi-genes)
- Avoid excess nitrogen — split urea into 3 applications; do not top-dress urea at heading
- Silicon application (Silica Gel @ 5 kg/acre foliar, or slag) increases structural resistance to blast penetration
- Ensure proper water management — shallow flooding at panicle initiation reduces leaf wetness duration
- Treat seed with Tricyclazole @ 1 g/kg seed (before nursery sowing) to prevent seedling blast
Quick Reference | त्वरित संदर्भ
- Causal organism: Magnaporthe oryzae (Pyricularia oryzae)
- Most critical spray timing: Panicle Initiation (PI) stage — preventive
- Best fungicides: Tricyclazole, Isoprothiolane
- Weather to watch: Humid nights below 22°C + morning dew = high blast risk
- Season peak: July–September (Kharif)
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