Pathogen biology, environmental conditions, and concentric symptoms
Alternaria solani survives on infected crop debris, volunteer plants, and solanaceous weeds, releasing airborne conidia during alternating wet and dry weather.
- Foliar lesions: Dark brown to black circular or angular spots with characteristic concentric rings resembling a target board.
- Chlorotic halo: Lesions are typically surrounded by a yellow chlorotic zone caused by fungal alternaric acid toxins.
- Progressive defoliation: Disease begins on lower, mature leaves and moves upward, exposing developing fruits to sunscald.
- Fruit and tuber rot: Causes dark, sunken, leathery lesions on tomato fruit stems and dark corky rots on potato tubers.
Preventative cultural controls and sanitation
Cultural management practices minimize fungal spore inoculum and reduce disease pressure in solanaceous crops.
- Crop rotation: Rotate solanaceous fields with non-host crops like maize, pulses, or brassicas for at least two seasons.
- Clean certified seed: Use certified disease-free potato seed tubers and treated tomato seeds.
- Pruning and staking: Stake tomato plants and prune lower senescent leaves to improve air circulation and reduce soil splash.
- Drip irrigation: Utilize drip irrigation rather than overhead sprinklers to keep foliage dry and inhibit fungal spore germination.
Chemical fungicide management and spray schedules
Apply preventative contact fungicides like Mancozeb 75% WP or Copper Oxychloride 50% WP before disease onset. Upon detecting initial target spots, rotate with systemic fungicides such as Azoxystrobin + Difenoconazole SC, Tebuconazole 25.9% EC, or Pyraclostrobin 20% WG. Ensure thorough spray coverage and observe label pre-harvest intervals.
Official source
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Indian Council of Agricultural Research (ICAR) ↗Related on KisanPe
Common questions
What causes early blight disease in tomato and potato?
Early blight is caused by the fungal pathogen Alternaria solani, which attacks leaves, stems, and developing fruits.
How can a grower identify early blight on plant leaves?
Look for dark brown circular leaf spots showing distinctive concentric rings surrounded by a yellow halo (target board symptom).
Which fungicides are effective against early blight?
Preventative protectants include Mancozeb and Copper Oxychloride; systemic options include Difenoconazole, Tebuconazole, and Azoxystrobin.
General guidance, not personal advice. For your farm, ask your local Krishi Vigyan Kendra or agriculture officer.
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