Farmers use a range of herbicides to control weeds however, with repeated and frequent use of the same herbicide or similar types of herbicides, weeds become resistant.
Herbicide resistance is the inherited ability of a plant to survive and reproduce, even after the application of a herbicide.
Australian graingrowers 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, graingrowers mitigate the development and spread of herbicide-resistant weeds.
These strategies include:
- Regular monitoring of weeds and escape weeds from previous herbicide applications;
- Small weed populations suspected of being herbicide-resistant controlled by spot treatment. The weeds can then be rogued and area ploughed, or a nonselective herbicide applied before weeds set seed;
- Restricting 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;
- Buying 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 testing has shown are still effective; and
- Using a weed destructor to pulverise weed seeds at harvest, killing at least 95 per cent of annual weed seed.
Mechanical rogueing methods are very effective when used in conjunction with chemical controls.
In addition, growers also have other options to disrupt weed cycles, such as altering sowing dates, row spacing, harvest times, increasing plant densities and crop rotation.
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District agronomists, who are familiar with resistant weeds in the region, can provide guidance 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 about submitting and testing suspected resistant weed samples, please contact shafiya.hussein@sa.gov.au
- The Grains Farm Biosecurity Program is an initiative of the Department of Primary Industries and Regions SA, 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.
