While many parts of the Western Australian grainbelt have been inundated with water in recent weeks, too often the lead-up to crop sowing across much of the State is dry and applying pre-emergent herbicides that might not persist in the soil can be risky.
Results from a project investigating the likely decay of some commonly-used products on a range of soil types, applied on several dates and with various levels of soil moisture at a site in Cunderdin will be discussed at the upcoming Grains Research and Development Corporation (GRDC) Grains Research Update, Perth.
This is the State’s premier annual grains research and innovation event and will be staged at Crown Perth on February 27-28. Registrations and program information is available on the Grain Industry Association of WA (GIWA) website.
The Cunderdin trial findings will be presented by Western Australian No Tillage Farmers Association (WANTFA) executive officer Dr David Minkey, who coordinated the two-year project and said the aim was to help growers develop effective weed management strategies when sowing wheat crops early into dry soil.
He said three of the most popular pre-emergent herbicides used by WA growers were found to decay slowly during a six-week period in dry soil conditions and could be used with confidence when dry sowing wheat on a range of soil types.
“This backed previous WA experiments that found pre-emergent herbicides could be applied months in advance of sowing under perfectly dry conditions and not decay,” he said.
“But in wet conditions, our 2014 and 2015 trials found decay was rapid – regardless of soil type - and this was further exacerbated when temperatures were warm.
“This highlights the risks of use of these herbicides very early before the season break.”
Dr Minkey recommended growers should not rely on pre-emergent herbicides to provide adequate weed control in wet conditions when sowing in April.
He said if sowing was carried out in wet soil in mid-April, when there would be significant crop competition from weeds, the research trials indicated that the efficacy of most herbicide options would have run-out.
“With a late April sowing, there is likely to be protection from the major flush of weeds with the common pre-emergent herbicide options,” he said.
“But some of these herbicides would offer limited protection from later flushes of weeds.
“This means predicting future rainfall events will be crucial for achieving good weed control from pre-emergent herbicides when dry sowing early.”
Dr Minkey said the WANTFA project, funded by GRDC, highlighted that when sowing early, there could be benefits in achieving better weed control from:
• Using a longer residual herbicide
• Delaying dry seeding until late April or early May (with a one week dry period to follow)
• Ensuring a low weed seedbank
• Using weed modelling systems to predict weed germination timing and levels.
He said if there was early rain, such as has occurred this year, it might be more effective to wait until surface and subsurface moisture has dried-out before sowing wheat crops.
Dr Minkey’s full paper being presented at the GRDC Grains Research Update, Perth will be available on the GIWA website.