Failure of Diabole cubensis, a promising classical biological control agent, to establish in Australia

The rust Diabole cubensis (Arthur & J.R. Johnston) Arthur was introduced into northern Australia as a classical biological control agent against the noxious wetland weed Mimosa pigra L. (Mimosaceae). Pre-release evaluation and observation in Mexico, Central America, and South America, the center of origin of D. cubensis, revealed a range of characteristics that suggested the rust had great potential to exert some control over M. pigra in Australia. This dry-season rust was cultured and field inoculations were carried out during the northern Australian dry season when ambient conditions were suitable for infection. Post-release assessments showed that M. pigra developed symptoms of rust infection in the field but that the rust failed to spread and therefore to establish in Australia. Analyses of the post-release assessments of D. cubensis in Australia pointed to gaps in the knowledge of the weed–pathogen ecology. The failure of the rust in light of performance of other biological control agents is reviewed.