Residual Herbicides

Where are residual herbicides commonly used?

Residual herbicides are used in broadacre farming before planting crops to keep paddocks weed-free, which allows new crops to establish. 

They’re also used to maintain productive grazing pastures by suppressing unwanted broadleaf weeds and annual noxious grasses. 

What forms do residual herbicides come in?

There are two popular forms of residual herbicide: 

• Liquid herbicides: Concentrates mixed with water and administered via boom sprayer to enable even application over large areas. 
• Granular formulations: Granules applied with spreaders or via aerial application. Some may be diluted with water, whereas others are distributed as-is.

Deciding between liquid and granular formulations

The choice between liquid or granular residual herbicides comes down to variables like application equipment, crop type, target weeds, and soil conditions. To determine the correct application method for your circumstances, read the manufacturer’s instructions, or contact us for advice.

How are residual herbicides applied?

Residual application will depend on your farming system and chosen product formulation. The most common application methods are: 

• Boom spraying: Where the herbicide is mixed with water and sprayed evenly over the paddock, usually before weeds emerge. 
• Granular spreading: Where small pellets or granules are spread mechanically, either by air or with a spreader, to release the herbicide into the soil over time. 

What to be aware of when using residual herbicides

If residual herbicides are not selected and used correctly, they come with some downsides. Here’s what to be mindful of before employing a residual herbicide: 

• • Crop rotation restrictions: Because residuals stay active in the soil for a long time, they can harm crops planted too soon after application. If a paddock is replanted before the herbicide has broken down, crop damage, poor germination, and crop failure can occur. Refer to the plant back intervals on the product label for more information.

• Risk of damaging desirable plants: If the herbicide moves in the soil or is applied incorrectly, non-target plants may face damage.

• Soil persistence: Some herbicides break down slowly in certain soil conditions, like when the soil is dry or has low organic matter. These conditions may lead to issues when planting the next season’s crops.

• Off-target movement: In some circumstances, residual herbicides can move from their intended area and leach through deeper soil profiles and groundwater. Runoff can occur, and the chemical can enter waterways.

• Herbicide resistance: Using the same active ingredient or relying on knockdown herbicides can encourage resistance in some weed species. It’s not common, but important to be aware of before use.

• Timing: Residuals must be applied before weeds germinate or before the crop is planted, depending on label instructions. 

Like all herbicides, it’s essential to read the manufacturer’s directions and follow label instructions when applying a residual herbicide.

For product recommendations or advice on specific weed challenges, please contact the Specialist Sales team.