Symptoms and Control Methods of Cotton Leaf Blight

Symptoms Also known as cotton Cercospora leaf spot. It mainly damages leaves. Infection usually occurs in the late growth stage of cotton. At first, many dark red small spots appear on the leaves, then expand into nearly round lesions with purplish red, slightly raised edges and brown centers. Under moist conditions, a white mold layer forms, which is the pathogen's conidiophores and conidia. Affected leaves break very easily.

Pathogen Mycosphaerella gossypina (Cooke) Earle, called cotton ball fungus, belongs to the Ascomycota fungi. The ascocarp is spherical and black. The ascospores are two-celled, with the upper cell wider and the tip pointed and slender, measuring 12-14 x 5-7 (μm). The asexual stage is Cercospora gossypina Coke, called cotton tail fungus, belonging to the Deuteromycota fungi. The conidiophores are brown, with 1-5 septa, measuring 70-450 x 4-7 (μm). The conidia are whip-shaped, colorless, with 6-16 septa, measuring 50-200 x 3-5 (μm).

Transmission route and disease conditions The pathogen overwinters as mycelium on diseased residues. In the following spring, under moist conditions, it produces conidia, which spread through wind, rain and insects. After infection, repeated infection occurs under rainy, high-humidity conditions or cool autumn conditions. Cotton plants infected by other diseases or with insufficient fertility, and sandy loam soil, are prone to the disease.

For control methods, see cotton ring spot disease.