Brown root rot, caused by an invasive pathogen Phellinus noxius, impacts diverse tree species in tropical and subtropical areas, including eastern and southeastern Asia, Australia, and the Pacific Islands. Little is known about the genetic diversity of this pathogen, its precise distribution, and how it is being spread. Genetic studies are underway to confirm the identity of the pathogen and examine its evolutionary history, which have revealed the existence of different genetic groups of the pathogen. With international collaborators, pathogen samples were collected in Japan, Taiwan, China (Hong Kong), Malaysia, Australia, and the Pacific islands (e.g., Guam, Saipan, American Samoa, Pohnpei, Kosrae, Palau). Ongoing genetic analyses are determining similarities and differences among pathogens from different areas to better characterize the pathogen, determine potential pathways of spread, and predict geographic areas that are at risk from this invasive pathogen. Continued collaborative studies with Colorado State University and Kookmin University in Seoul, Republic of Korea, will use more detailed genetic information to determine worldwide movement, potential pathways of spread, and help develop measure to prevent additional introductions of this aggressive forest pathogen.This information is used for bioclimatic models to predict global regions at risk from the invasive pathogen. Key Findings of the study reveal that the brown root-rot pathogen is killing diverse tree species in eastern and southeastern Asia, Australia, and Pacific islands. Genetic studies show that this invasive pathogen comprises distinct genetic groups that occur in different locations. Preliminary findings indicate that this pathogen is likely invasive and has been introduced to multiple regions.