Pre-emergent herbicides are a popular and effective way to control weeds. This fact sheets covers how they work and how they interact with the environment.

Key points

• To choose the right herbicide, growers need to know which weeds are in the paddock and whether their seeds are shallow or deep.
• Check if a herbicide can evaporate (volatilise) or break down in sunlight to decide how to apply it without losing it.
• A herbicide’s solubility affects how much rain is needed for it to work. It also impacts how easily weeds and crops absorb it, and whether it might leach into deeper soil layers, possibly harming crops.
• Sandy or low organic soils don’t hold onto herbicides well, making them more available for weeds and crops but also more likely to leach away.
• Herbicides that stick to soil and organic matter need higher application rates. They stay where applied and last longer, unless the soil moves.
• Soil pH can change how long herbicides last and how easily plants can absorb them.
• How long a herbicide lasts and how it breaks down will affect how long it controls weeds. It also impacts when sensitive crops can be planted afterward.
• Rain after application helps herbicides soak into the soil and reach weeds or crops. Rain and temperature also affect how fast herbicides break down.
• The amount of herbicide applied influences how long it lasts and how well it works with crops.

Want a printed copy?

Printed copies of some publications are available for growers, advisers and farming systems groups, for personal use and distribution at GRDC events.

View our current stocklist.

Contact GroundCover Direct on 1800 11 00 44 or email ground-cover-direct@canprint.com.au to request copies. Publications are free but postage and handling costs may apply.