Strangling the resistance: Integrated weed management

South Australian grower John Lush has gone back to nature to help overcome a major impediment to farm profitability — herbicide resistance.

He is using plants to compete with plants — in this case, cereals versus annual ryegrass — assisted by other management tools.

He and his family grow about 1,000 hectares of crops a year in the 400 mm rainfall belt near Mallala in the lower north of SA. With the emergence of herbicide resistance in ryegrass a few years ago, major modifications were made to farm management practices. "We changed the focus from early sowing and maximum yields to maximum yields with ryegrass control," Mr Lush explained.

"In fact, we virtually changed everything."

How it works

"We use high seeding rates of from 90-140 kg/ha with high rates of fertilisers so weeds don't have a chance to see daylight," Mr Lush said. "We sow the bread wheats, for instance, at about 100 kg/ha and the less competitive durums at 140 kg.

"We sow Skiff barley, which is very vigorous, in paddocks with some ryegrass, and we cut hay from the worst-infested paddocks to prevent seed set.

"We have also changed from grass herbicides to knockdowns pre-sowing, and we croptop our grain legumes with Grammoxone."

Mr Lush said his program aimed at maximum control of ryegrass in two consecutive years and then "monitoring, monitoring, monitoring" to ensure ryegrass populations remained corralled by:

  • spraytopping (the year before sowing);
  • early cultivation to encourage ryegrass germination;
  • application of knockdown herbicides, pre-sowing;
  • direct seeding with narrow row spacings about a month after the break and after ryegrass is sprayed; and
  • as a last resort, stubble burning to reduce ryegrass seed levels.

Integrated weed management

The Lush's herbicide resistance mitigation strategy is a practical example of the integrated approach promoted by the GRDC-supported Cooperative Research Centre for Weed Management Systems. The principle is that a single action is unlikely to overcome what is a major threat to the viability of cereal production. Mr Lush said that the action taken to combat herbicide resistance on his farm was "definitely a package".

"If it involved just one answer it would be dead easy," he said, "but it doesn't".

Mr Lush said the practice of using high seeding rates and vigorous varieties such as Skiff to stifle ryegrass growth did not mean that plants were unduly stressed if the season soured. "A single plant is much more capable of sustaining a main stem and single tiller under high density and moisture stress than is a single system able to sustain many tillers under stress," he said.