Biological control of Giant Rat’s Tail grass utilising Nigrospora oryzae

Abstract

Giant Rat's Tail grass (GRT) (Sporobolus pyramidalis and S. natalensis) has established itself as a significant problem to the profitability and sustainability of grazing environments across Eastern Australia. A combination of underutilisation by grazing animals due to unpalatability, resilience and persistence especially in poor soils, and an aggressively high seeding rate have seen GRT spread across many coastal and sub-coastal regions of Queensland.

In some areas, GRT infestations have dramatically decreased livestock producers' economic viability and lowered their land values. Current infestations are collectively costing the pastoral industry in the vicinity of $60 million per annum through lost production and control (Bray and Officer, 2007). In many cases, the stocking rates have been halved on pastures heavily infested with GRT. In addition, the age of turn off of fat cattle on these pastures has been extended by up to 12 months (Bray 2008). The potential area of infestation in Queensland covers 108 million hectares or 60% of Queensland (Anon, 1999).

This project investigated the ability of the fungus Nigrospora oryza to cause die back in GRT and subsequent potential as a biocontrol agent of GRT. This fungus has been proposed as a pathogen of Giant Parramatta Grass (GPG) (S. fertilis), a closely related species to GRT.