Wick wiper application in Giant Rat’s Tail Grass management: evaluating herbicide efficacy and rates

Giant Rat’s Tail Grass (GRT, Sporobolus natalensis) is a robust and aggressive colonizer of disturbed areas, producing large quantities of seeds that remain viable for up to 10 years. GRT infestations significantly reduce pasture productivity and animal production, costing the pastoral industry substantially in lost production and control costs. Effective management practices are essential to control current infestations and prevent further spread. Wick wiping is a herbicide application method that uses grass height differential achieved via slashing and regrowth to target taller weeds such as GRT, while avoiding shorter, desirable pasture grasses. There are limited herbicides currently available for GRT control, with glyphosate and flupropanate being the only registered options. A mix of these two herbicides is common practice in wick wiping of pastures infested with GRT, yet there is a knowledge gap around optimal application rates. Flupropanate has faced supply shortages in Australia, and resistance in some weedy Sporobolus grass populations is evident. Thus, it is important to find alternatives. We are conducting two trials to determine optimal herbicide treatments and application rates for controlling GRT. To simulate wick wiping, a micropipette was used to apply treatments to the leaf of potted plants. The first trial investigates the efficacy of eight herbicide treatments on mature S. natalensis tillers. The second trial examines the effect of varying herbicide application rates on the survivability of mature S. natalensis, with a constant active ingredient concentration. The trials were initiated in late December 2024/ early January 2025, with visual plant damage score data to be assessed 6 weeks, 3 months, 6 months, and 12 months post-treatment. Data from the 6-week and 3-month assessments will be presented. This study will contribute further to the body of knowledge on effective and sustainable wick wiper treatment strategies for GRT.