![]() In both cases, the longer the period that leaves are wet, the better - for the pathogen. Growth of lesions and production of new spores are also favored by leaf moisture. The leaf surface must be wet in order for spores to germinate. What constitutes “favorable conditions”? There are two key factors: temperature and leaf-wetness. This rapid reproductive cycle explains why the disease can expand so rapidly and defoliate a crop within a matter of weeks. Under favorable conditions, this complete cycle - from a spore landing on a leaf to production of thousands of new spores - takes about one week. These lesions produce new spores, which are spread by wind or running water, or carried by workers or implements onto new foliage. Fungal mycelia grow and expand, producing characteristic brown, circular lesions with dark concentric rings like a target board. Early blight disease begins when Alternaria spores (conidia) land on the leaf surface, germinate, and penetrate the leaf tissue. In four years of trials, we have seen reductions of 9% to 52% in the total marketable fruit due to early blight, in unsprayed plots.Īlternaria solani, the organism that causes early blight, is a fungal pathogen that attacks several solanaceous crops including potato and eggplant. Uncontrolled, early blight can completely defoliate tomato plants and cut short the harvest. However, it is not until mid- to late August that we see rapid expansion of the disease throughout the foliage. In our disease management trials at the University of Massachusetts, and in farm fields, the first symptoms usually develop in mid to late July. Contrary to what its name suggests, this disease normally appears late in the season, as plants develop a full load of ripening fruit. Early blight is probably the most common and widespread of foliar diseases in field-grown tomatoes in New England.
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