The leaf spot in turmeric is caused by soil borne fungal pathogen Colletotrichum capsici. The pathogen is favored by high moisture and dense planting. The main symptoms are appearance of irregular brown spots with grey centre on the upper leaf surface. The symptoms typically starts from younger leaves. As the disease progress the spots may merge together resulting in drying and wilting of entire leaves. Once the disease mature this spots were covered with small black dots which contain fungal spores.

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http://farmer.gov.in/imagedefault/ipm...