Technical Abstract: Host range determination is essential to determine the safety of a classical biological weed control agent and successfully petition for release of the agent in a non-native area. Recently Henderson’s mixed model equations (MME) were adapted to evaluation of host ranges of biological control pathogens by incorporating genetic relatedness, in the form of DNA sequences, with disease evaluation data among target and non-target plants to generate best linear unbiased predictors (BLUPs) of disease reaction among these plant species. The MME were shown to have multiple advantages over other evaluation methods and were also more conservative and safer than other analytical methods. However, there were calls to provide some other validation. In this study, the host-ranges of two biological weed control pathogens previously released in the USA were evaluated with the MME and historical host-range data. Results showed that: BLUPs conformed to currently available information on host range; the BLUPs were accurate predictors of host range; no unforeseen non-target effects could be expected in nature; and confirmation of the narrow host range of the two pathogens provided further validation of the use of the MME in host-range determination.