Controlling weed seed at harvest may be growers’ best line of defence in combatting the on-going battle against herbicide resistance.
With headers now dotted across winter crop paddocks in New South Wales and Queensland, the Grains Research and Development Corporation (GRDC) is reminding growers that driving down the weed seed bank is critical to managing herbicide resistance.
GRDC Manager Regional Grower Services – North, Sharon O’Keeffe said harvest weed seed control played an important role in stopping weed seeds from entering the soil and reduced the seed bank build prior to the following season.
While resistance to one mode of action herbicide is extremely common in the north, she said there were many cases of multiple or cross resistance now occurring particularly in problem weeds like wild oats.
“Wild oats (Groups A, B and Z) and fleabane (Group M) are the most widespread resistant species while resistance to glyphosate is present in Awnless barnyard grass, ryegrass and windmill grass within certain areas,” Ms O’Keeffe said.
“Driving down the weed seed bank is growers’ best defence against herbicide resistance and that centres on two key considerations - dealing with the weed seeds already existing in the soil and stopping additional weed seeds from entering the soil.
“Dealing with weed seeds already existing in the soil requires growers to control any new emergences and stop seed set and double knock tactics are commonly and successfully used in the north to achieve this.
“Stopping weed seeds from entering the soil requires alternative, non-herbicide tactics and one of those available to growers is harvest weed seed control.”
Harvest weed seed control was originally developed in Western Australia in the wake of escalating issues with herbicide resistance.
It centres on collecting, destroying or burning weed seeds that are present at harvest and has been particularly effective in problem species such as wild radish and annual ryegrass.
According to Ms O’Keeffe the greatest opportunity for harvest weed seed control lies with species that set seed above a harvesting height (at least 15 cm above ground level) and retain seed through the traditional winter crop harvesting periods.
“If implemented regularly, the use of one non-herbicide weed seed control tactic every harvest will play a key role in keeping northern cropping land productive and extending the useful life of existing herbicide chemistries,” she said.
One of the simplest tactics is narrow windrow burning which a number of growers in the northern region have begun to utilise as part of an integrated strategy.
Narrow windrow burning is best suited to non-cereal crops such as lupins, canola and field peas and cereal crops yielding less than 3 tonnes per hectare.
Further information on harvest weed seed management, herbicide resistance and integrated weed management strategies is available from the GRDC’s Integrated Weed Management Hub www.grdc.com.au/IWMhub
Links to GRDC Update papers and reports on weed management are available from the Grain Orana Alliance website www.grainorana.com.au
Caption: GRDC Manager Regional Grower Services – North, Sharon O’Keeffe says it is imperative that growers are not complacent about the threat of herbicide resistance.
GRDC Manager Regional Grower Services, North
0409 279 328
Sarah Jeffrey, Cox Inall Communications
0418 152 859
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