CSU Blog Series

2019 has seen FFN partner with Charles Sturt University to provide FFN members with access to a series of the University’s studies directly relevant to young farmers. This second study looks at Integrated Weed Management. Please contact CSU or FFN should you wish to find out more.

Why does integrated weed management matter?
A key focus of research at the Graham Centre for Agricultural Innovation is integrated weed management to reduce dependence on herbicides and boost returns to grain growers.

The Centre, an alliance between Charles Sturt University and the NSW Department of Primary Industries (DPI), has a long history of weed science research.

For the past 25 years herbicide resistance testing at Charles Sturt has evaluated specimens sent in from around Australia.

Charles Sturt Emeritus Professor Jim Pratley said the testing has shown the trends in herbicide resistance over time.

“Our work has identified the first resistance in ryegrass to glyphosate and to triflualin, and in wild oats to mataven,” Professor Pratley said.

“It is clear that weeds have responded to farming practice and there is a need to have diversity in management practices so that one control measure does not encourage a weed to proliferate.”

The growth of no-till and conservation farming has also led to a different cohort of weeds, particularly in the summer fallow. Changes in climate are also creating weed problems not before seen in some areas, for example fleabane in southern Australia.

The Grains Research and Development Corporation (GRDC) invested in Graham Centre weed research focused on not only managing herbicides for weed control but seeking out non-chemical measures to reduce dependence on herbicides to preserve their efficacy for longer.

Competitive crops to beat the weeds
Research is examining the mechanisms and traits that make certain cultivars or genotypes of wheat, barley and canola better at suppressing weeds.

Professor Leslie Weston said one mechanism under study as a means for effective weed suppression is the ability of plants to exude chemicals into the soil around the roots, or root exudation, as a defence mechanism against competition from neighbouring plants.

Other cultivars effectively suppress weeds due to competition for resources such as water, nutrients and sunlight due to their early vigour, both above and below-ground, and their canopy or root architectural traits.

Key points:

  • The research into wheat and barley genotypes has found that crop height and vigour are important early in the season for competitive crops and subsequent weed suppression.
  • Before flowering, certain crop cultivars can release significant quantities of allelochemicals from an actively growing root system which contribute to plant defence against pests, including weeds.
  • Tillering characteristics, both above and below the ground, along with canopy and root architecture are also important for the crops ability to out-compete the weeds.
  • These characteristics may also improve the yield potential by providing greater access to moisture and nutrients.

It’s hoped the findings can be used by plant breeders to incorporate these weed suppressive traits into more commercial grain cultivars.


Weed suppression in the summer fallow
Another area of research has focused on the role of crop stubble and residue on weed suppression over the summer.

The research is examining both the physical or mulching impact but also the chemical interactions including the change of nutrients and metabolites in the soil.


Key points:

  • Heavy stubble suppresses the establishment of weeds
  • Leave the stubble for as long as possible
  • Disc planters are one way to be able to manage heavy stubble loads


Cover crops provide options in mixed farming rotations
Graham Centre research in the south west slopes of NSW has examined the role of cover crops in suppressing winter weeds.

The research over three-years has examined annual legumes like sub clover, bladder clover, gland clover, serradella and biserrula, and mixtures of pasture species including lucerne, phalaris and cocksfoot.

The research assessed the impact on weeds including barley grass, sow thistle, poppy, ryegrass, fumitory, capeweed and Paterson’s curse.

It found the rapid establishment of pasture species, as well as optimal production of biomass, contributes to suppression of winter weeds.

It also suggests that newer varieties, like the hard-seeded annual legumes biserrula and serradella are able to supress competition through the release of chemicals and interactions with soil microbiota.


Key points

  • Variety and species selection is important
  • Careful grazing management of cover crops is needed to ensure there is enough biomass to out-compete weeds for resources like water and sunlight
  • Research aims to understand the chemical mechanisms that help some of the newer varieties of annual legumes to suppress weeds


Further reading:
‘Cropping practices influence incidence of herbicide resistance in annual ryegrass (lolium rigidum) in Australia’ published in Crop and Pasture Science
‘The weed suppressive ability of selected Australian grain crops; case studies from the Riverina region in New South Wales’ published in the journal Crop Protection.
‘Performance and weed suppressive potential of selected pasture legumes against annual weeds in south-eastern Australia’ published in the journal Crop and Pasture Science.

Graham Centre plant systems research pathway leader Professor Jim Pratley: jpratley@csu.edu.au
Charles Sturt Herbicide Resistance Testing Service Dr John Broster:  jbroster@csu.edu.au
Plant Interactions Research Group Professor Leslie Weston:  leweston@csu.edu.au

Inspection of weed research trials at the Graham Centre’s annual Twilight Field and Crop Walk held in September each year