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The marigold (Calendula officinalis) is an herbaceous plant used by its beautiful yellow or orange flowers, in bordures, gardening and as cut flower. It is largely diffuse in the world, not only for the beauty of his flowers or his use in cosmetic, but for being resistant, of easy cultivation and for it low demanding in environmental conditions. In Mendoza it is very used as ornamental plant and every year is affected by a disease called powdery mildew. In Argentina there are mentioned as etiological agents of the disease different species of the generous Erysiphe, and Oidium erysiphoides. Nevertheless the teleomorphic form wasn't described until 1991 in Corrientes and Córdoba. There, it was reported as Sphaerotheca fusca. In 2004 in Mendoza, it was observed over marigold cultures a severe powdery mildew attack. Studying the problem, over the typical powder of the disease, the presence of black bodies was observed. This motivated to determine the etiology of the disease in Mendoza. Several samples of marigold plants affected were taken at different places. At the laboratory, morphological and morphometric studies permitted the identification of Podosphaera fusca (=Sphaerotheca fusca) as causal agent of the powdery mildew of the marigold in Mendoza. [ABSTRACT FROM AUTHOR]