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A plant disease in which the principal symptom is limited areas of necrosis on the leaves. There are numerous causes of leaf spots - mineral imbalance, insects, weather conditions, viruses, bacteria, and fungi. The leaf spots may be minor symptoms or a particular phase of a disease that develops other, more characteristic, symptoms. Bacteria and fungi are the usual causal agents of the diseases in which leaf spots are the main symptom. Angular leaf spot of cucumber is caused by the bacterium Pseudomonas lacrymans. Fungal leaf spots affect most crop plants and common pathogenic genera are Septoria, Botryodiplodia, Colletotrichum, Gloeosporium, Cercospora, Alternaria, and Helminthosporium.
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