Grain growers are being encouraged to keep residual herbicides front of mind when controlling weeds this summer, as what is applied now will have an impact on winter crop choices.
GRDC weeds manager Jason Emms said predicting how long herbicides would persist in the soil was an ongoing challenge for growers who were often mindful of this factor.
“Many herbicides can persist in the soil for extended periods of time,” Mr Emms said.
“Herbicides for residual weed control need to provide weeks or months of persistence in the soil to achieve their desired weed control objectives.”
Many elements influence the time it takes for herbicides to break down.
As a general rule, if the top 10 cm of soil isn’t moist then little herbicide degradation is occurring.
With the Bureau of Meteorology flagging that the peak of the La Niña weather event has already been and gone, growers should avoid betting on wet conditions to wash away chemicals.
Other breakdown factors to consider are: soil temperature, microbial activity, soil type, soil pH, soil organic matter and the chemistry of the herbicide used and how it degrades.
The GRDC has a comprehensive resource to help growers, agronomists and farm advisers when planning herbicides on the GRDC Herbicide Behaviour webpage.
Visit the page at: https://grdc.com.au/resources-and-publications/resources/herbicide-behaviour
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