ONE OF Australia’s leading weed management specialists has said farmers should embrace heavier crops as a means to outcompete problem weed species such as rye and brome grass.
Chris Preston, of the University of Adelaide, said ryegrass resistance to post-emergent herbicides was now common in many high rainfall zones, such as southern Victoria and south-east South Australia, and he urged growers to implement an integrated strategy to minimise the risk of herbicide resistance.
As part of this, he said high biomass crops could play a role in outcompeting weeds.
“In trials, a high biomass canola species, Hyola 750TT, significantly reduced the number of ryegrass spikes at harvest compared to the two other cultivars in the trial at harvest,” Dr Preston told a meeting at last month’s Grains Research and Development Corporation (GRDC) update in Bendigo.
He said growers could halve the amount of ryegrass that sets seed simply by switching from an open pollinated to a hybrid canola.
“Crop competition against the weeds is important, especially as we look to retain the efficacy of herbicides.”
Dr Preston said trial results at Lake Bolac in Victoria showed that on a pure basis of lowering ryegrass numbers a high intensity herbicide strategy was the best method.
“It is more costly, you can find yourself spending $100 a hectare on ryegrass control along, but the effectiveness is there.”
He said for growers in areas where there was the potential for multiple ryegrass germinations during the season, this higher cost strategy was the safest.
“At trials at Frances, in SA, we saw a low intensity ryegrass control program lead to a high number of ryegrass plants setting seed.
“The message is clear, in high rainfall zones, low intensity management plans don’t work.”
Dr Preston also said growers needed to look long term with their rotations to lower the amount of seed.
“If there is a high burden of grass weeds, one year of a break crop is good, but two is better.”
“We have found that with two break crops you can virtually control any weed seed set.”
He said the innovation of glyphosate tolerant, triazine tolerant (RT) canola gave growers a stronger suite of management tools.
“Having RT canola in the system gives growers the chance to utilise different sets of chemistry and to use both post-emergent and residual herbicides.”