Fighting herbicide resistance — with western 'double-knock'

With 70 per cent of WA growers practising no-tillage, the move back to cultivation may be slow.

ATTENDEES AT the recent WA Agribusiness Crop Updates 2002 heard that growers may need to consider using full-cut cultivation at seeding if they are to overcome glyphosate resistance in annual ryegrass, through 'double-knock' techniques.

Spraying with glyphosate or Spray.Seed, followed by full-cut cultivation, represents a form of double-knock to minimise the risk of glyphosate resistance developing.

WA Department of Agriculture Weeds Research Officer in Geraldton, Peter Newman, said there was more than one type of double-knock, with another option being a full rate of glyphosate, followed a week later by a full rate of Spray. Seed.

"However, according to sales of these herbicides, this type of double-knock isn't really happening in WA," he said.

While this practice is agronomically sound, the drawbacks of this method are that it is costly, time-consuming (as spraying needs to be repeated) and sowing is often delayed.

Cultivation updated

Mr Newman explained that full-cut cultivation does not necessarily mean reverting to old techniques and machinery. Rather, there are new machinery options that combine knife points with wide sweeps and press wheels. "This is a one-pass machine which furrow-sows and handles stubble," he said.

With 70 percent of WA growers practising no-tillage, the move back to full-cut cultivation may, however, be slow.

"Some farmers are very passionate about no-tillage and a percentage will not even consider full-cut cultivation," Mr Newman said. Nevertheless it was something for growers to consider as they buy new machinery in coming years.

Glyphosate and no-till alone: recipe for disaster

Mr Newman stressed that he wasn't suggesting full cut was the only answer, but said using only glyphosate and no-till would worsen the resistance problem.

Australia leads the world in weed herbicide resistance, with annual ryegrass in sandplain areas of WA's northern agricultural region heading the country's herbicide resistance problem.

Grower comments

Mullewa grower Matthew Micke adopted the full-cut system through purchasing new machinery for last year's seeding program and fitting it especially for use with trifluralin. The seeder was set up for ribbon seeding and wide points, rather than knife point.

Mr Micke said he was very pleased with the results after one season. After using the double-knock (i.e. glyphosate followed by full cut), ryegrass count was zero and the crop had even germination and good growth.

"One of the secrets of this technique is that it shears weeds that haven't popped through at the point of sowing," Mr Micke said. "This gives plants a better start, as they germinate at the same time as ryegrass rather than after it, giving plants a level playing field."

He wasn't concerned about changing from no-till farming, especially because of the savings it made. "I saved $9,500 on glyphosate in one season and there were a lot of paddocks that didn't need glyphosate," he said.

"I also had excellent nutrient mineralisation, which can be a problem on sandy soils."

Program 4 Contact: Mr Peter Newman 08 9956 8555

Region North, South, West