Puccinia kuehnii is an important airborne fungal pathogen of sugarcane, causing orange rust disease. P. kuehnii has been present in the Asia–Oceania region for over a century. The first report of this pathogen in the Western Hemisphere was in 2007, when it appeared in Florida, U.S.A. The main objective of this diagnostic guide is to provide detailed information about symptoms and signs of sugarcane orange rust as well as taxonomy, geographic distribution, isolation, identification, and storage of P. kuehnii. We also highlight the management strategies used in recent years to control this devastating fungal disease. This diagnostic guide will help facilitate future research focusing on fungal isolation procedures, genetics, and population studies of this pathogen.