Resumo. ABSTRACTThe root-rot of erva-mate, caused forFusariumspp.,Rhizoctoniasp. andPythiumsp., is the main disease ofthe culture and causes serious damages in nurseries and forest stands. However, few studies exist regardingto the epidemiology of this disease. Thus, the present work studied and described the main epidemic aspectsrelated to erva-mate root-rot in nurseries and forest stands. For that, nurseries and forest stands were chosenfor studies in Vale do Taquari, RS state, where flowers, fruits, seeds, plantlets, seedlings and soil werecollected for laboratory analyses. It was observed that the pathogens can enter in the patho-system throughthe flowers, because 80% of them presented contamination ofFusariumsp. and 15% ofRhizoctoniasp.Moreover, the obtaining method and stratification of the seeds, used in the nurseries, contribute to theincrease of contamination, reaching 100% of the seeds in the moment of sowing. It was also observed thatcontaminated seedlings may be symptomless and, after transplanting in the field, contaminate pathogen freeareas. Pathogenicity tests with some isolates showed their capacity of causing the disease.