ADJUSTING seeding rates, seed size and row spacing had a dramatic impact on ryegrass numbers at trial sites in Kojonup that were blanketed in the plant.
The trials were sown by the Australian Herbicide Resistance Initiative (AHRI) last year, in partnership with the University of Adelaide, South Australia, with investment from the Grains Research and Development Corporation.
AHRI research agronomist Mike Ashworth said the trial was all about trying to increase the competitiveness of canola against weeds, especially annual ryegrass.
"One thing we've found is that we're fast running out of herbicides for canola, that herbicide resistance is going through the roof and that it's spreading fast," Dr Ashworth said.
"What we want to do is work out how to reduce the amount of herbicide that we need to apply to a plot and figure out how to make that crop as competitive as possible to overcome the weeds by themselves.
"Weeds are opportunistic, they're going to take root and do well where we leave behind any resources, such as water, nutrients and light."
In one of the trial paddocks AHRI was testing the impact of seed size, with a small seed of less than 1.8 millimetres in diameter and a large seed size greater than 2mm.
"The paddock had three seed rates, consisting of 20 plants per square metre, we've got 35 plants p/m2 and 50 plants p/m2, as well as both a hybrid variety, Hyola 559 and an open pollinated (OP) variety, Bonito,'' Dr Ashworth said.
He said the two seed sizes were commonly used by growers so they wanted to measure the effect.
"In this trial, we found that seed rate was important, going to 50 plants p/m2 over 35 is really important," Dr Ashworth said.
"But the most important factor of all is making sure your seed size is big, that 0.2mm makes a huge difference.
"When we increase our seed size, we get an increase in our crop yield, we also get that same increase in our competitiveness against weeds."
When it comes to the different varieties, Dr Ashworth said while growers could get better competition out of a lower sowing rate with a hybrid variety, they could still get excellent control out of an OP.
"What growers need to do is make sure that you do not skimp on seeding rates," he said.
"The trials have all shown that if we can keep that seeding rate up about 50 plants p/m2 and put a lot of effort into grading out seeding for the large size, we can achieve excellent results from OPs."
In another trial paddock, AHRI tested the impact of row spacing by using the same seeding rates and plant varieties, but with either 22.86 centimetre (nine inch) or 45.72cm (18in) row spacings.
Dr Ashworth said wherever they used the wider row spacing, they had a dramatic increase in ryegrass density, proving narrower spacing was better for competition.
"That's simply because we're setting the crop up in a way that it can't utilise all of those resources," he said.
"With the wide row plot, at 18in, there is an awful lot of light, a lot of moisture and a lot of space for those ryegrass plants to take hold.
"Plus some of those treatments have had a lot of herbicide applied to them and we still had a lot of ryegrass."
The one thing Dr Ashworth said growers should never do was utilise herbicides in the absence of crop competition.
"A good herbicide will fail when it's grown in the absence of competition," he said.
"The weed will have enough resources to metabolise the herbicide within itself and continue to grow."