Gamba grass (Andropogon gayanus Kunth) is a tall tufted perennial grass that grows up to 4 m in height with tussocks up to 70 cm in diameter. It reproduces sexually through wind-assisted cross-pollination and the light and fluffy seeds that are spread by the wind. Natural spread is relatively slow, as 90 % of seeds fall within 5 m of the parent plant and less than 1% fall more than 10 m away. However, it has spread over long distances as a consequence of being sold and planted as a commercial pasture plant. The native range of gamba grass extends across the tropical and subtropical savannas of Africa, from Senegal on the west coast to Sudan in the east, south to Mozambique, Botswana and South Africa.

Gamba grass is an invasive grass species of national significance in Australia, but provides valuable feed for cattle and is generally not considered to be a problem within fenced, well-managed cattle paddocks. However, the grass has rapidly spread outside paddocks, mainly due to its superior competitive advantage and resource use efficiency over native grass species. Chief among the grasses’ impacts is that it replaces native grasses and causes profound effects on the savanna biodiversity. The high biomass of the tall grass also increases fuel load and affects fire regimes, creating extremely intense fires that can lead to dramatic and rapid declines in tree canopy cover. These high fire intensities can have socio-economic impacts as they can result in higher risks of property damage, loss of life and impacts to cultural sites.

Biological control of the species is long considered should a suitable agent be discovered. Successful biological control of the grass requires an agent that will weaken the stems of the tall grass and cause it to slant; thereby limiting seed dispersal and reducing fuel load of wildfires, whilst still providing grazing for cattle. The primary aim of the project is to identify suitable sampling sites (of the grass) in South Africa and to find potential biological control agents that could compromise the structural integrity of the grass stems; with a particular focus on the galling wasp of the genus Tetramesa. Tetramesa spp. appear to have radiated within the Poaceae, many species of which show high levels of host-specificity and inflict significant damage to their host-plants. Several Tetramesa spp. are essential agricultural pests of which some can be effective biocontrol agents of invasive plants e.g. Tetramesa romana on Arundo donax in the USA.

Last Modified: Fri, 28 Sep 2018 14:49:11 SAST