Brome RIM puts weed strategies to the profitability

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Highly herbicide-resistant ryegrass has received much of the integrated weed management attention, but for many growers brome management is just as demanding, especially in the sandy, low-rainfall regions where it grows strongest.

GRDC research confirms brome grass is one of the most costly weeds in Australia and is the number one grass weed enemy in many regions. Reasons include:

  • a lack of reliable pre-emergent herbicide control options in cereals
  • the evolution of later-germinating populations in no-till systems
  • the ability of brome grass to grow well on sandy soils where crop competition can often be poor
  • limited selective herbicide options in cereals and
  • increasing resistance risk.

In addition, harvest weed-seed practices, which can be highly effective with ryegrass, typically have much less impact on brome due to its early seed shedding.

While growers and advisers have explored strategies for managing herbicide-resistant ryegrass using the University of Western Australia’s (UWA) RIM (Ryegrass Integrated Management), there was no equivalent for brome grass. To address this gap CSIRO has developed Brome RIM, through the GRDC Stubble Initiative and in collaboration with UWA, the University of Adelaide and grower groups such as Mallee Sustainable Farming.

Testing options

Brome RIM allows growers and advisers to quickly set up crop/pasture and management sequences and test a full range of crop and brome management options for impact on crop yields, weed populations and profitability for up to 10 years. The tool has already been used in many workshops and trials with growers keen to test the cost-effectiveness of practices such as crop sequence changes, narrow windrow burning, reduced reliance on Group B herbicides and greater crop competition for seed-set suppression.

CSIRO used a Brome RIM scenario to analyse the long-term value of a practice change that increases crop competition. Options to improve crop competition on sandy soils include using soil wetting agents on non-wetting soils, on-row seeding options, new seeding systems or more competitive varieties. Here researchers consider the value of a seed-placement innovation such as near-row sowing that could increase establishment of cereals on non-wetting sandy soils to the equivalent of increasing wheat seeding rates from 60 kilograms per hectare to 90kg/ha but without additional seed cost.

Over a 10-year wheat/barley/wheat/lupin crop sequence the scenario assumed only one brome plant per square metre set seed in the previous year. Sowing was at a standard seeding rate in a no-till system, one week after the break in cereals and dry in lupins. Cereal herbicides were glyphosate knockdown (double-knock in the first wheat) and pre-emergent trifluralin (trifluralin + metribuzin in barley). Lupin herbicides were pre-emergent simazine, post-emergent clethodim and crop-topping.

The high cereal crop competition scenario resulted in an overall average net benefit (gross margin) of $23/ha/year (12 per cent) and was able to maintain low weed numbers (Figure 1). Without high crop competition it is likely that there would need to be some reliance on Group B/Clearfield® options in cereal crops to maintain weed populations.

 

Figures 1 and 2

Graphic showing the Brome RIM model showed that higher crop competition improved annual crop gross margin and net profit again

The Brome Rim model showed that higher crop competition improved the annual crop gross margin and net profit gain (left) by reducing the weed populations (right) over a 10-year wheat/barley/wheat/lupin crop sequence.

Graphic showing the Brome RIM model showed that higher crop competition reduced weed populations over 10 years

For growers weighing up brome management options, Brome RIM can help identify break-even investment rates and other potential benefits such as increased flexibility to reduce Group B herbicide use. Brome RIM and other RIM versions are available for free download from the Australian Herbicide Resistance Initiative website.

GRDC Research Codes CSP00186, MSF00003

More information:

Dr Rick Llewellyn, CSIRO Agriculture
08 8303 8502
rick.llewellyn@csiro.au

UWA Australian Herbicide Resistance Initiative Brome RIM