With much of this year’s winter crop now sown, results of pre-emergent herbicide applications will be evident over the coming weeks.
Ineffective performance of pre-emergent herbicides due to a large range of factors can often result in weeds escaping control, replenishing the weed seed bank for years to come.
To help agronomic advisers over the coming weeks with evaluation of the performance of pre-sowing or at-sowing herbicide applications on their grain grower clients’ properties, the Grains Research and Development Corporation (GRDC) has published a new resource.
The manual, titled Soil behaviour of pre-emergent herbicides in Australian farming systems – a reference manual for agronomic advisers, is available on the GRDC website.
Developed for the GRDC by consultants Mark Congreve and John Cameron from ICAN (Independent Consultants Australia Network), the manual covers a broad range of information needed to optimise and understand results from pre-emergent herbicides.
According to Mr Cameron, the manual is specifically targeted to the needs of grains advisers.
“Much of the material included is highly specific, and previously relatively hard to access in a format that meets the needs of grains advisers.
“As such, it is a document that a large number of grains advisers will find contains significant new information of value to their day-to-day recommendations,” Mr Cameron said.
Mr Congreve says the manual covers much of the base science that underpins what is represented on the product labels.
“It does not replace the labels, but assists advisers in interpreting how the pre-emergent herbicides are likely to perform and to understand why they have performed as they have in specific situations,” Mr Congreve said.
As herbicide resistance increases, particularly to knock down and in-crop selective herbicides, greater reliance is often placed on pre-emergent herbicides.
“While not immune from resistance, as evidenced by widespread resistance to products such as trifluralin and group B residual herbicides, several key pre-emergent herbicides still have good efficacy on most populations of weeds,” Mr Congreve said.
“As such, they provide an excellent buffering tool to maintain profitable farming systems as the industry transitions to a more diverse range of weed management tactics that also includes non-herbicide based management tactics.
“Increased reliance on pre-emergent herbicides means advisers need to understand how these tools behave in the soil and the environmental factors that influence their performance. It is with this in mind, that the GRDC has published this new manual.”
Issues covered include stubble and crop interception; loss pathways such as photo degradation and volatilisation; the position of the herbicide in the soil; the influence of soil texture and cation exchange capacity; solubility; binding to clay and organic matter; the influence of soil moisture; half-life and breakdown mechanisms and impacts on crop rotation.
John Cameron, ICAN
Mark Congreve, ICAN
Sharon Watt, Porter Novelli
GRDC Project Code