Determining the value of pasture to limit serrated tussock invasion

Geoff Millar, Aaron Simmons, Karl Behrendt, Marja Simpson, Warwick B. Badgery

Research output: Book/ReportResearch report not released to public

Abstract

Serrated tussock (Nassella trichotoma) is a highly invasive perennial grass weed that is a major problem to livestock producers in the High Rainfall Zone of south eastern Australia. The weed drastically impacts on the productivity of grazing systems and adds significant cost in control. Flupropanate is the chemical commonly used to control serrated tussock and the method of application is often determined by the cost effectiveness of the spraying operation (ie aerial, boom or spot spraying). Controlling serrated tussock using broadacre control methods of aerial or boom spraying will kill the serrated tussock, but also productive native grasses (eg wallaby grass - Rytidosperma spp and microlaena - Microlaena stipoides) that provide competition, which can result in higher invasion rates in the future. To add further complexity, climate change will impact on the spatial distribution of serrated tussock and may affect future control methods, and understanding these impacts is important for future planning. The project determined the most effective areas to control serrated tussock and prioritised direct management (spraying) with indirect management (reducing invasion with competitive pastures). The study also identified the potential current and future distribution of serrated tussock for Australia, and the Central Tablelands region of NSW, based on future climatic variables, which were refined with land-use types that can influence serrated tussock establishment.This pilot study demonstrated that it is possible to determine the whole-farm economic and environmental impacts of different serrated tussock management scenarios for a typical property on the Central Tablelands of NSW. While the biophysical modelling clearly showed a reduction in the invasion rate of serrated tussock and less spraying with increased perennial pasture and lower stocking rates, this advantage was not enough to offset the lower cost of boom spraying or in some scenarios 'no control' when compared to spot spraying that had very high labour costs. However, spot spraying that was 4 to 6 times more efficient (MI3 climate and 50% annual and 50% perennial pasture scenarios run at 4 and 6 DSE/ha) than the scenario in this study improved the economic performance of this strategy to be better than no control or boom spraying. It was also clear that it was not viable to run a wether enterprise alone at this scale (400ha) and the results indicated that loss minimization through low levels of inputs, which is a common behaviour in the management (or lack of management) of serrated tussock, often gave the better whole-farm economic returns. There were clear environmental benefits of reduced greenhouse gas (GHG) emissions, through less displaced production, and the maintenance of perennial pastures would also likely reduce erosion and improve biodiversity outcomes. Therefore a balance view of control needs to be taken, where the short-term benefit to the landholder and the longer-term public good view are considered. This study was done within the context of future climate change, which will reduce future potential distribution of serrated tussock in the Central Tablelands of NSW, but may increase the invasion rates in pastures due to lower pasture biomass in autumn.
Original languageEnglish
PublisherNSW Department of Primary Industries
Commissioning bodyNSW Weeds Action Program
Number of pages100
Publication statusPublished - 2016

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    Millar, G., Simmons, A., Behrendt, K., Simpson, M., & Badgery, W. B. (2016). Determining the value of pasture to limit serrated tussock invasion. NSW Department of Primary Industries.