WHILE grain growers in many areas are looking anxiously for a break in the weather, experts warn them to be vigilant about monitoring and managing early weeds this season.
Grains Research and Development Corporation (GRDC) crop protection officer north, Vicki Green, said many growers had already dry sown a proportion of their winter program and there was now the potential risk of a weed blow out when it rained as pre-emergent herbicide effectiveness could be compromised by the dry start to the season.
“Growers trying to juggle large cropping programs will dry sow winter crops, but this has the potential to compromise weed management” Mrs Green said.
“This is further complicated when pre-emergent herbicides have been applied and dry conditions prevail. So, we now just want to remind growers of the need to be prepared and monitor and manage for early in-crop weed control.”
She also encouraged growers to be selective about the paddocks they do dry sow, favouring those that were kept clean last season or planting crop varieties that have a wide range of post-emergent weed control options.
It is a position supported by ICAN weed specialist, Mark Congreve, who is involved in a GRDC investment designed to improve grower and advisor understanding of best practice pre- and post-emergent herbicide application.
Mr Congreve said dry sown crops were likely to have weeds emerging with the crop, particularly if no pre-emergent herbicide was used.
“So, these crops are likely to need an early post-emergent application,” he said.
“My concern is that effective post-emergent herbicides are limited and need to be correctly timed, so leaving weed control ‘until later’ while other paddocks are planted may mean post-emergent herbicides are likely to be less effective. For example, if you want to target ryegrass in wheat and barley with Boxer Gold post-emergent then it has to be applied before the ryegrass reaches the three-leaf stage.”
Mr Congreve said if growers had applied a pre-emergent herbicide and sown dry, how it performed would depend on: the actual herbicide used, soil moisture at application, how well the herbicide was incorporated, the amount of rainfall received when the season eventually breaks and the depth from which the weed seeds were germinating (on the surface or from depth).
“Determining the effectiveness of pre-emergent herbicides in these conditions is difficult and varies depending on the situation,” he said.
“But the message for growers who have already applied a pre-emergent with their dry sowing is really to monitor crops for early weeds and to be prepared to implement any additional control measures early for maximum effect.”
Mr Congreve said growers should consult with their advisors to make informed decisions around the choice of post-emergent grass active herbicides to optimise their performance in the paddock.
He said understanding the resistance status of the weeds, the different modes of action available (herbicide biochemistry), how post-emergent herbicides enter the plant and what can be done to maximise uptake (formulation, application and adjuvants) was key to effective weed control in-crop.
For more information about how different pre-emergent herbicides may be affected by dry conditions go to https://weedsmart.org.au/webinars/
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