This work is the result of activities included in the cooperative project between Asociación Ribera Norte (ARN) and the Department of Plant Pathology, School of Agronomy, University of Buenos Aires. ARN is a non-governmental organization created in 1993 mainly for the management of the Reserva Ecológica Municipal Ribera Norte, a preservation area located in San Isidro (North of Buenos Aires), within the Provincia Paranaense region. The aims were to identify diseases in native plant species growing there. Light brown leaf spots with thin brown margins and narrow yellow halos were observed on Terminalia australis (mean disease severity: 25%). The pathogen was isolated, inoculated on healthy plants, reisolated from infected leaves and identified as Alternaria tenuissima. Similarly, another leaf-spot disease was observed on Salvia guaranitica, characterized by reddish brown large spots developed from the apexes and margins towards the centre of the leaves, reaching the veins in some cases (mean severity: 20%). Pathogen isolation, inoculation and reisolation led to the identification of A. alternata as the causal agent of the disease. Unusual heavy rain is analyzed as disease conductive.