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Early blight is caused by the fungi Alternaria solani and A. alternata.
The disease causes damage particularly in hot and dry continental climates, but is accentuated by irrigated cultivation.
Early blight is encouraged by plant ageing and very specific weather conditions :
• high temperature (20-25° C) with dew during the night allowing infection,
• alternating damp and sunny periods for the development of conidia and sporulation.
The spores are spread by the wind and rain splash.
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• On leaves : well-defined necrotic blemishes, of variable size, located more often on the bottom leaves, concentric rings on the large blemishes.
• On tubers : brown and black rot, very dry, quite typical, with shrinking.
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