Herbicide resistance makes tackling tussock tricky

Serrated tussock. Picture: Jo Powells, South East LLS

Serrated tussock. Picture: Jo Powells, South East LLS

Serrated tussock is a widespread weed across the Southern Tablelands of NSW and is well known to many Monaro land managers who have been battling it for well over 40 years.

One of the weed control options for managing serrated tussock is herbicides. However, only two main herbicides options are commonly used, Flupropanate (eg Taskforce, Tussock) and Glyphosate. Flupropanate has been the most frequently used herbicide for serrated tussock control on the Monaro since the plant was first discovered in the region in the 1970s.

Jo Powells, senior agriculture advisor with South East Local Land Services (LLS), has just concluded a two year project investigating flupropanate resistance in serrated tussock on the Monaro.

“This project was driven by observations and local commentary around poor efficacy of control of the weed using the herbicide,” Ms Powells said.

“The first year results from the project indicated that there were a few populations of plants that were resistant to flupropanate but that further testing was needed to confirm the extent of the problem.”

Jointly funded by LLS and the Australian government’s National Landcare Program, LLS staff worked with Snowy Monaro Regional Council biosecurity officers and local land managers to identify locations where herbicide resistance might have developed.

The second year of the project expanded the sampling to over 40 sites across the region over summer 2017/18. The collected seed was then sent to a herbicide resistance testing facility in South Australia for analysis.

“Eighteen samples were found to have a high level of resistance to the herbicide flupropanate. A further 15 were identified as having a weak, but developing resistance to the herbicide,” Ms Powells said.

“Importantly, this year’s results identified resistance or developing resistance in plants from across the Monaro region, not just in a few localities.

“Whilst flupropanate resistant biotypes were confirmed widespread, susceptible plant populations were also widely recorded.”

The development of resistance comes from the continual and long term reliance on any one herbicide (in this case flupropanate) within some plant populations. Although the first flupropanate resistant population of serrated tussock was found in Victoria in the early 2000s, additional populations have since been found in both the northern and southern tablelands of NSW.

Additional information can also be found on the South East LLS website at www.southeast.lls.nsw.gov.au.