Weed management is critical to profitable farming. Out-of-control weeds can take over crops and reduce yields. This manual outlines how to use pre-emergent herbicides to drive weed numbers down.

Pre-emergent herbicides can play a key role in a weed control strategy. They are effective at curbing the spread of weeds. Pre-emergent herbicides are not as impactful on seed bank numbers when used alone. However, when used among a suite of tactics, they can make a big difference.

Pre-emergent herbicides offer:

• an alternative mode of action compared to many post-emergent options
• less selection pressure on future post-emergent herbicide applications
• removal of early season weeds, which protects crop yield. This is more effective than later post-emergent treatments and in weedy paddocks.
• cost savings, especially in the fallow, where many knockdown applications are sometimes needed
• less time pressure on other spraying operations, both in crops and in the fallow
• significant help in patch eradication, for example where a weed blowout can be GPS logged, and a pre-emergent herbicide applied.

Weed seeds will always be present in the soil after a cultivation event. They often end up in spots perfect for germination. Applying a pre-emergent herbicide after the last cultivation helps control weeds. This prevents them from emerging and adding more seeds to the soil.

Some crops have few post-emergent options. This includes grass weed control in sorghum, or broadleaf weed control in pulses. That is why they often rely on pre-emergent herbicides for in-crop weed control.

Contents of manual

The manual covers the following topics:

• the importance of controlling weeds in broadacre field crops
• the value of pre-emergent herbicides
• common objections to the use of pre-emergent herbicides
• factors influencing the activity of pre-emergent herbicide, including:
  • interactions prior to incorporation
  • incorporation
  • herbicide behaviour in the soil
  • herbicide properties affecting soil binding and availability.
• how herbicides are taken up by germinating seedlings
• crop safety
• information about key residual herbicides
• properties of pre-emergent herbicides used in Australian grain production systems
• references.

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