Early Blight
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When it strikes
About
Early blight (Alternaria solani) is a common warm-season disease of tomato and potato that builds through summer, starting on the oldest leaves and working upward, reducing yield and exposing fruit to sunscald.
Symptoms
Brown spots with concentric rings forming a target or bullseye pattern, surrounded by yellow halos, on older lower leaves first. Severe defoliation and dark leathery lesions near the stem end of fruit.
Organic Treatment
Remove affected lower leaves, mulch to stop soil splash, and spray copper or a Bacillus subtilis biofungicide. Maintain even watering and adequate nitrogen to slow progression.
Chemical Treatment
Chlorothalonil or mancozeb every 7–10 days, alternating with strobilurin (azoxystrobin) or difenoconazole during heavy pressure.
Prevention
Rotate crops on a 2–3 year cycle, mulch beneath plants, stake for airflow, and avoid overhead irrigation. Choose tolerant cultivars where available.