Biocontrol of Sporobolus Grasses African survey for weedy sporobolus biocontrol agents

Summary

Five grasses (Sporobolus africanus (Parramatta grass), S. fertilis (Giant Parramatta grass), S. jacquemontii (American rats tail grass) and S. natalensis and S. pyramidalis (both Giant rats tail grass), collectively known as the weedy sporobolus grasses, are serious pastoral weeds in Australia, affecting productivity, property management and, ultimately, land values. Because chemical and physical control methods are usually uneconomic, biological control offers a practicable solution.

The Queensland Department of Natural Resources and Mines, supported by Meat and Livestock Australia, undertook a project to find potential biocontrol agents. The search was conducted in southern Africa, through the department's South African Field Station, because three of the grasses (Sporobolus africanus, S. natalensis, and S. pyramidalis) are native to that region. Over two years, areas infested with these grasses were surveyed from Western Cape Province in the south to northern Botswana, resulting in the collection of over 70 phytophagous insect species and 23 plant pathogens.

Two organisms were selected as being potential biocontrol agents and recommended for further study. The leaf smut, Ustilago sporoboli-indici attacked all three grass species and was very damaging. Spores of the smut could be germinated and clean plants infected in the laboratory. A eurytomid wasp, Tetramesa sp., was found infecting the grasses and causing malformed inflorescences. However, it was not cultured in the laboratory.