News

By Shafiya Hussein, Grains Biosecurity Officer, South Australia

The economic impact of weeds on the Australian grains industry due to cost of control and reduced yields, is estimated at $4 billion annually.

Weeds compete with growing crops, contaminate grain, and can possibly cause health problems.

In controlling weeds, farmers use a range of herbicides to manage the problem, however, with repeated and frequent use of the same herbicide or similar types of herbicides, weeds become resistant.

Herbicide resistance can be described as the inherited ability of a plant to survive and reproduce after a herbicide that would normally kill the weed, has been applied.

South Australian grain growers typically struggle with resistant weeds such as ryegrass, sow thistle, brome grass, barley grass, wild oats, wild radish, and wild turnip. In addition, grain receival standards clearly stipulate tolerance levels to the presence of weed seeds.

Sustainable weed control involves using herbicides with different modes of action in conjunction with integrated weed management strategies.

By incorporating diverse crop management strategies, grain growers mitigate the development and spread of herbicide resistant weeds.  These strategies include:

• Regularly monitoring of weeds and escape weeds from previous herbicide applications.
• Small weed populations suspected of being herbicide resistant can be controlled by spot treatment. The weeds can then be rogued, and area ploughed, or a nonselective herbicide applied before the weeds set seed.
• Mechanical rogueing methods are very effective when used in conjunction with chemical controls.
• Restricting the movement of weed seeds to other paddocks.
• Cleaning down machinery before driving into another property. Paddocks with resistant weed issues should be worked on last.
• Purchasing certified weed-free seed each sowing season.
• Cleaning seed retained on-farm and remove seed dockage
• If herbicide resistance is confirmed by a diagnostics lab, using herbicides that the testing has shown are still effective should be used.
• Using a weed destructor can pulverise weed seeds as grains are harvested killing at least 95% of annual weed seed.

In addition, growers also have options to disrupt weed cycles such as altering planting dates, row spacing, harvest times, increasing plant densities and crop rotation.

Consulting with district agronomists who are familiar with resistant weeds in your region can guide you on the best management strategies and herbicide options.

Growers should always follow recommended application rates, adhere to withholding periods, check the weather to ensure efficacy and prevent spray drift and always follow safety data sheet instructions.

For more information on resistant weeds and their prevention and management visit the following industry websites:

• GRDC Integrated Weed Management Hub
• WeedSmart
• Australian Glyphosate Sustainability Working Group
• CropLife Australia’s Herbicide Resistant Weeds list

For more information about submitting and testing suspected resistant weed samples, please contact Shafiya Hussein at shafiya.hussein@sa.gov.au

The Grains Farm Biosecurity Program is an initiative of the Department of Primary Industries and Regions South Australia, Plant Health Australia, and Grain Producers Australia to improve the management of, and preparedness for, biosecurity risks in the grains industry at the farm and industry levels. Visit the Grains Farm Biosecurity website for more information.