- Scientific Name
- Alternaria porri
- Kingdom:
- Fungi
- Phylum:
- Ascomycota
- Subphylum:
- Pezizomycotina
- Class:
- Dothideomycetes
- Subclass:
- Pleosporomycetidae
- Order:
- Pleosporales
- Family:
- Pleosporaceae
- Genus:
- Alternaria
- Species:
- Alternaria porri
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Purple blotch
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- Scientific Name
- Alternaria porri
- Kingdom:
- Fungi
- Phylum:
- Ascomycota
- Subphylum:
- Pezizomycotina
- Class:
- Dothideomycetes
- Subclass:
- Pleosporomycetidae
- Order:
- Pleosporales
- Family:
- Pleosporaceae
- Genus:
- Alternaria
- Species:
- Alternaria porri
Purple Blotch is a common fungal disease affecting onion and related Allium crops.
Overview of Purple Blotch
| Disease Name | Purple Blotch |
|---|---|
| Causal Agent | Alternaria porri (fungus) |
| Hosts | Onion, garlic, leek, shallot |
| Symptoms | Small, water-soaked lesions on leaves that enlarge to purple or brown blotches with concentric rings; lesions often surrounded by yellow halos. As disease progresses, leaves may wilt and die. |
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Key Features
-
Lesions often appear on leaves and leaf sheaths.
-
Early symptoms are small, water-soaked spots.
-
Lesions enlarge rapidly under warm, humid conditions.
-
In severe cases, foliage blights, reducing bulb size and yield.
-
Favorable conditions: warm (20–30°C), humid weather with prolonged leaf wetness.
Disease Cycle
-
Overwinters on infected plant debris and seed.
-
Produces spores (conidia) that spread by wind and rain splash.
-
Infection requires moisture; spreads quickly in wet weather.
✅ Management Strategies
| Strategy | Recommendations |
|---|---|
| Cultural | Use disease-free seed; crop rotation; remove debris; avoid overhead irrigation; plant in well-drained soils. |
| Resistant Varieties | Where available, use tolerant or resistant cultivars. |
| Chemical Control | Apply fungicides such as chlorothalonil, mancozeb, or strobilurins at early signs of disease and repeat as needed. |
| Monitoring | Scout regularly during warm, wet conditions; remove severely infected leaves to reduce inoculum. |
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Importance for Growers
Purple blotch can cause significant yield loss and reduce marketability of onion crops if not managed effectively.
Purple blotch
| Alternaria porri |
Login to access our suggested solutions.
Purple Blotch is a common fungal disease affecting onion and related Allium crops.
Overview of Purple Blotch
| Disease Name | Purple Blotch |
|---|---|
| Causal Agent | Alternaria porri (fungus) |
| Hosts | Onion, garlic, leek, shallot |
| Symptoms | Small, water-soaked lesions on leaves that enlarge to purple or brown blotches with concentric rings; lesions often surrounded by yellow halos. As disease progresses, leaves may wilt and die. |
Â
Key Features
-
Lesions often appear on leaves and leaf sheaths.
-
Early symptoms are small, water-soaked spots.
-
Lesions enlarge rapidly under warm, humid conditions.
-
In severe cases, foliage blights, reducing bulb size and yield.
-
Favorable conditions: warm (20–30°C), humid weather with prolonged leaf wetness.
Disease Cycle
-
Overwinters on infected plant debris and seed.
-
Produces spores (conidia) that spread by wind and rain splash.
-
Infection requires moisture; spreads quickly in wet weather.
✅ Management Strategies
| Strategy | Recommendations |
|---|---|
| Cultural | Use disease-free seed; crop rotation; remove debris; avoid overhead irrigation; plant in well-drained soils. |
| Resistant Varieties | Where available, use tolerant or resistant cultivars. |
| Chemical Control | Apply fungicides such as chlorothalonil, mancozeb, or strobilurins at early signs of disease and repeat as needed. |
| Monitoring | Scout regularly during warm, wet conditions; remove severely infected leaves to reduce inoculum. |
Â
Importance for Growers
Purple blotch can cause significant yield loss and reduce marketability of onion crops if not managed effectively.