Nectandra lanceolata Nees & Mart. ex Nees (Lauraceae), known as ayuí-saiyú, laurel cinnamon or yellow laurel, is an endemic species from SE South America. In Argentina, this tree constitutes a typical component of "Provincia Paranense, Distrito de las Selvas" valued by its timber and its interest as ornamental. The aim of this study was to identify the causal agent of the powdery gall in Nectandra lanceolata. Material was collected at "Jardín Botánico Carlos Spegazzini, Facultad de Ciencias Agrarias y Forestales, UNLP". Samples with over-developments covered by powdery whitish masses were processed for their analyses under light and scanning electron microscopes. The microscopic features of the basidia and the basidiospores together with the macroscopic characteristics of the galls allowed us to identify Drepanoconis larviformis (Basidiomycota, Exobasidiales, Cryptobasidiaceae) as the causal agent of powdery gall in N. lanceolata. In Argentina, D. larviformis was reported growing on N. porphyria, N. falcifolia and Ocotea puberula, thus our findings constitute the first record on N. lanceolata for this country. [ABSTRACT FROM AUTHOR]