How to prevent and control cucumber target spot disease
2024-09-09
1. Key Conditions for Disease Development
- Pathogen: Corynespora cassiicola (fungus)
- Favors: 27–30°C, >85% RH, leaf wetness >4 hours
- Spreads via: wind, water splash, tools, infected seeds/residues
- Starts on lower leaves (yellow spots → brown target-like lesions)
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2. Integrated Prevention & Control Measures
A. Agricultural & Sanitation Practices
- Resistant varieties: Choose tolerant cucumber cultivars
- Crop rotation: ≥3 years with non-Cucurbitaceae (rice, corn, legumes)
- Seed treatment:
- Hot water: 55°C for 25 min
- Or 0.1% Carbendazim soak 1 hour
- Remove inoculum:
- Rogue and burn/discard severely infected leaves/plants
- Deep plow residues post-harvest
- Healthy seedlings: Use 60-mesh insect nets to block vectors
B. Environmental & Water Management (Critical)
- Reduce humidity:
- Greenhouse: ventilate to keep RH <80%; avoid night condensation
- Open field: wide row spacing, avoid dense planting
- Irrigation:
- Drip or furrow only; no overhead sprinklers
- Water early morning; keep foliage dry
- Temperature control:
- Day: 28–33°C; night: 16–18°C (suppresses spore germination)
- Greenhouse: 42–45°C heat treatment for 2 hours (closed) to kill spores
C. Biological & Organic Control
- Bacillus subtilis, Pseudomonas fluorescens (preventive sprays)
- Sodium bicarbonate (baking soda):
- 50 g + 10 L water + 3–4 drops detergent
- Spray every 1–2 days ×2–3 times at early onset
- Chitosan, phosphite (K/Zn/Cu): boost immunity
- Copper formulations (quinoline copper, copper hydroxide) 600–800×
D. Chemical Control (Effective Options)
Start early at first symptoms; rotate modes of action to avoid resistance.
Preventive
- Azoxystrobin (25% SC) 1500×
- Mancozeb + carbendazim 800–1000×
Curative (choose one)
- Difenoconazole + azoxystrobin (e.g., Amistar Top) 1500×
- Pyraclostrobin + boscalid (e.g., Cabrio Top) 1500×
- Prochloraz (25% EC) 1500×
- Tebuconazole / Hexaconazole 3000×
3. Full Prevention Program Summary
- Before sowing/planting: resistant seed + disinfection + rotation
- Seedling stage: clean nursery + netting
- Growing:
- Low humidity + good ventilation
- Drip irrigation; no wet foliage
- Early signs: spray biocontrol or low-toxic fungicide
- Outbreak: use systemic fungicides (rotate groups)
- Post-harvest: clean up all debris
4. Key Tips for Success
- Humidity control is more important than frequent spraying
- Rotate fungicides (triazole, strobilurin, copper) to delay resistance
- Spray leaf undersides (infection starts there)
- Combine fungicides with seaweed extract/phosphite to speed recovery
- Usage:
- Spray both sides of leaves, especially lower/older leaves
- Interval: 7–10 days; 2–3 applications
- Pre-harvest interval (PHI): follow label (usually 3–7 days)