Control of thatch grass (Hyparrhenia rufa) with herbicides

Abstract

Thatch grass (Hyparrhenia rufa) is a perennial tussock-forming grass native to tropical Africa that can form dense clumps up to 3 m tall. Now established across northern and eastern Australia, it commonly occurs along roadsides and rail corridors, where it outcompetes native vegetation and contributes to increased fire frequency and intensity. It is also beginning to spread into adjacent woodlands and pastures, posing an emerging threat to rangeland biodiversity and productivity. Chemical management options are limited, and field experience suggests flupropanate provides poor control. To expand available control options, a glasshouse herbicide screening trial is underway using potted thatch grass plants. The trial is evaluating a range of herbicides commonly used for perennial grass control, including both non-selective and selective active ingredients. A single rate is being assessed for each product, selected using operational guidance and label recommendations for perennial grasses. Visual damage observations at 10 weeks after treatment indicate that imazapyr (240 g/L) applied at 4.2 L/ha and haloxyfop (520 g/L) applied at 800 mL/ha may provide strong control of thatch grass. The trial will continue for a total of six months, and plant mortality and dry biomass will be quantified at the end of the experiment. A follow-up rate refinement trial will be conducted for the best-performing treatments identified in the screening phase, and findings will be presented. Collectively, these trials will identify herbicides for subsequent field evaluation and support improved thatch grass management recommendations for land managers. Trial data will also support the lodgement of a new minor use permit application with the Australian Pesticides and Veterinary Medicines Authority, to extend control options available for thatch grass in Queensland.