Global Agriculture

Collaborative weed control a winner against Feathertop Rhodes grass

01 November 2023, AU: New research has found that collaborative and agronomic weed management strategies can reduce the spread of Feathertop Rhodes grass (FTR) in Queensland and New South Wales.

The research which was supported by GRDC and industry partners found that when neighbouring land managers worked together and utilised integrated weed control tactics, infestations of highly mobile weeds like FTR were significantly reduced.

FTR is one of the most significant weed species in Queensland and NSW farming systems due to its widespread distribution, impact on grain yield, and its cost and difficulty to control. The problematic weed is also rapidly becoming a problem in southern and western grain growing regions of Australia.

The weed is well adapted to zero-till farming systems that are highly dependent on post-emergent herbicides. This has resulted in several FTR populations becoming resistant to Group M (glyphosate) and more recently Group A herbicides.

Research and paddock experience have shown that vigilance in monitoring and implementation of a suite of tactics is essential for successful management of FTR. Despite the adaptability of FTR, there are some ecological weaknesses that can be exploited to improve management success, including that:

  • most seed will germinate from a depth of zero to two centimetres;
  • the seed is relatively short-lived; and
  • if seed production is stopped for 18 months, the seedbank can be exhausted relatively quickly.

GRDC grower relations manager – north Vicki Green says the recently finished area wide management (AWM) for cropping systems weeds project – which was supported by Australian Government Department of Agriculture, Fisheries and Forestry, Cotton Research and Development Corporation, Australia’s national science agency CSIRO and other industry partners – found large-scale weed management practices such as roadside slashing were an effective tool to help manage FTR .

“The traditional approach for tackling weeds has been to focus on paddock or farm scale management. Instead, this project has focused on an area-wide approach to weed management,” Ms Green says.

“We’re seeing that when weeds over the entire landscape can be reduced, everyone in that area benefits. This project was all about bringing land managers together to identify weed concerns and to investigate what it would take for a more collaborative approach to be incorporated and successful.

“Collaborative weed management is particularly relevant when we’re dealing with weeds with mobile seed such as FTR.

“The challenge has been that a weed of concern for a grain or cotton grower may not be one that legally needs to be managed on the roadside. FTR is a perfect example.

“Starting the conversation between adjoining land managers has helped to identify where there’s opportunity for improvement.”

The AWM project has also allowed researchers to consider alternative management options at the interface of different land uses.

Working with the Millmerran Landcare group in southern Queensland for the past two years, CSIRO researcher Brett Cocks has been assessing the impact of slashing roadsides. As part of this work, areas were slashed five times a year just prior to seed-set and at the end of the growing season.

Mr Cocks says that one roadside site has been monitored for 14 months and preliminary results suggest frequent slashing is working.

“We’re seeing very positive results so far, and it’s evident that roadside slashing may be a good option for controlling the movement of seed, but collaboration and consistency is key,” Mr Cocks says.

In a bid to reduce the spread of weeds at paddock boundaries, the trial is also investigating how FTR competes with sorghum sown at different row spacings.

“We are investigating whether we can manage the edge of the paddock separately from the rest of the paddock to control weed spread,” he says.

“We have replicated trials in a grower’s paddock that adjoins the road, with sorghum sown at three different row spacings – 25 centimetres, 50cm and 100cm.

“If growers are planting sorghum and have grass weed problems there are limited chemical control options available. We want to see if a feasible option for growers is to use agronomic practices, such as reduced row spacing around the edge of the paddock, to reduce the spread of weeds from paddock boundaries.

“If we can control annual weeds and stop them from setting seed, councils, landholders, and the wider community all reap the benefits.

It is early days, but Mr Cocks says the 25cm row spacing results were looking promising.

“There are no weeds growing between the rows, compared with the 50cm and 100cm row spacings that are full of weeds.

“Given that FTR is also mobile in both irrigation and flood water, irrigation ditches are another area of concern for weed spread.”

Replicated trials in areas adjacent to irrigation ditches are being investigated with sorghum planted at 25cm, 50cm and 100cm in the same paddock.

“We need to analyse the data fully, but preliminary results are the same with no weeds between the 25cm rows, while the 50cm and 100cm rows are full of FTR,” he says.

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