A survey of fungal pathogens associated with cane tibouchina, Tibouchina herbacea (Melastomataceae), was conducted in the neotropics, concentrated in south and southeastern Brazil and aimed at finding potential biological control agents for this herbaceous invasive weed for introduction into Hawaii. Numerous fungal species were found, including five cercosporoid fungi. Four new taxa are described and illustrated here: Passalora tibouchinae, Pseudocercospora subsynnematosa, Pseudocercospora tibouchina-herbaceae and Pseudocercospora tibouchinicola. A phylogenetic analysis of the ITS and TEF-1α regions of the three new species of Pseudocercospora was conducted and confirmed their separation as distinct taxa as indicated by morphological and cultural features. Additionally, Cercospora apii is reported for the first time on T. herbacea. Among the species of fungi described in this study, two appear particularly promising for use in a biological control program because they were found to cause severe disease on T. herbacea: Passalora tibouchinae and Pseudocercospora subsynnematosa. Additional tests, including host-specificity screening, will be required in order to confirm this potential.