Alternaria
Scientific Name:
Scientific Name:
Crops:
Crops:
Potato
Biology
Control Method
Biology
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Definition
Alternaria is a fungal disease caused by the fungus Alternaria solani. It mainly affects the leaves of plants in the Solanaceae family, but can also infect stems and tubers. It is favoured by hot and humid conditions, and often occurs when crops are sparse or weakened.
Development Lifecycle
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Survival : The fungus survives in plant debris, soil, or on infected seeds.
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Contamination : Spores (conidia) are dispersed by wind, rain, irrigation, or tools.
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Germination : In the presence of humidity and favourable temperatures (20–30 °C), spores germinate and infect plant tissues.
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Spread : Fast, especially if planting density is low and ventilation is poor.
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Symptoms
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Brown to blackish spots (< 2 cm) on the leaves, initially lower.
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Concentric rings visible in the spots (bull’s eye appearance).
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Presence of dark, multicellular , club-shaped spores.
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The spots spread to the upper leaves, causing the foliage to gradually dry out.
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On tubers : black, round, dry spots, sometimes depressed.
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Risk of confusion with natural senescence at the end of culture.
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Contributing factors
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Brown to blackish spots (< 2 cm) on the leaves, initially lower.
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Concentric rings visible in the spots (bull’s eye appearance).
-
Presence of dark, multicellular , club-shaped spores.
-
The spots spread to the upper leaves, causing the foliage to gradually dry out.
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On tubers : black, round, dry spots, sometimes depressed.
-
Risk of confusion with natural senescence at the end of culture.
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Control Method
Preventive control
- Crop rotation with non-susceptible species (3–4 years).
- Destruction of plant residues after harvest.
- Use of healthy and certified seeds.
- Proper plant spacing to promote aeration.
Cultural control
- Balanced fertilization to avoid nitrogen stress.
- Avoid overhead irrigation during periods of high sensitivity.
- Harvesting of tubers in dry weather to avoid contamination.
Chemical control
- Preventive fungicide treatments or at the first symptoms:
- Products based on mancozeb, chlorothalonil, azoxystrobin, difenoconazole…
- Respect for intervals between applications and pre-harvest intervals.
Ipm
- Regular monitoring of crops.
- Targeted interventions according to the thresholds of harmfulness and weather forecasts.
