Biological control of weedy sporobolus grasses by two host specific agen ts

Summary

Five exotic Sporobolus spp., collectively known as the weedy sporobolus grasses, are serious weeds along the eastern seaboard of Australia. They are of extremely low palatability and cattle cannot utilise them, and are also invasive and easily spread to new properties and areas. Biological control investigations commenced in 2000 with surveys of southern Africa, where S. pyramidalis, S. natalensis and S. africanus originate. Some 70 phytophagous insect species and 23 plant pathogens were found but only two organisms were considered potential biocontrol agents; the leaf smut Ustilago sporoboli-indici L. Ling and the stem wasp Tetramesa sp. 
These two agents were studied in this project. Techniques to culture the smut were developed and it was found to be infective for Australian populations of four of the target species, but not the American S. jacquemontii. However it was also infective on four Australian native Sporobolus spp. and was therefore rejected. All attempts to rear the stem wasp failed and as this is an essential prerequisite for further study, work on this agent was discontinued. Although other areas such as Asia and North America could be searched, the prospects for biological control of these grasses are not good.