Two assessment methods for crown rot were compared: the widely used, categorical 0–5 scale and depth of rot penetration. Both were very highly correlated; the latter was more sensitive. The development of a bioassay for testing for crown rot pathogens and control methods is described. The rotting of green peel disks dipped in spore suspensions was significantly correlated with crown rot progress of whole clusters for both highly pathogenic C. musae and weakly pathogenic F. moniliforme isolates using inoculum concentrations covering a range of five orders of magnitude. The bioassay is specific to crown rot pathogens and detects efficient control measures. Because it is reliable, simple and rapid, it is suggested as a routine pre-screen for biocontrol agents against crown rot. The steps required for the establishment of a representative bioassay are explained and the final, optimised practical protocol is described.