Aug 18 2020

Protect crops, beat weeds with Backrow

Power residual herbicides in suboptimal conditions

For growers seeking the best possible start this Autumn, adjuvant Backrow will be a crucial addition to residual herbicides pre- and peri-emergence to protect crops and beat weeds. With increasing grass-weed resistance and suboptimal soil and application conditions threatening herbicide efficacy, improving herbicide performance has never been more important. The addition of Backrow will be vital to help mitigate the effects of very wet or very dry conditions that lead to poor weed control and poor crop competition. 

Backrow – delivers 3 major advantages

  • Improved weed control in poor application conditions
  • Improved weed control in very dry and very wet soils
  • Improved crop safety in wet soils


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    Conditions impacting herbicide performance

    Optimising herbicide contact with germinating weeds is a vital component of successful weed control but when it comes to pre and peri-emergence applications, it’s not as straightforward as you might think. Residual herbicide performance depends on good application and soil conditions, with sufficient uptake in soil water by the roots and shoots of germinating weeds. Herbicide placement and positioning in the soil is therefore vital but several factors threaten success.

    Spray drift and clods lead to poor coverage

    The performance of residual herbicides is heavily reliant on effective coverage across the soil surface to ensure full contact with germinating weeds. In poor application conditions, spray droplets can drift off course leading to poor coverage, whilst cloddy seedbeds can hide weed seed from spray droplets. Although drift reducing nozzles help to reduce drift, the coarser spray droplets do reduce coverage and this risks weeds escaping control.

    Protect crops, beat weeds with Backrow

    Very dry and very wet soils lead to poor weed control

    With a lack of soil moisture residual herbicide activity is reduced. Only in the presence of soil moisture can herbicides be absorbed into the roots and shoots of germinating weeds. In dry soils, herbicide active ingredients with high adsorption tendency (see Fig 1. below) bind even tighter to soil organic matter. With heavy rain, herbicides with moderate to high mobility can be washed below the weed germination zone preventing uptake into weeds.

    The implications of herbicide characteristics, soil type and soil moisture

    Residual herbicides need to be dissolved in soil water in the top 5cm of the soil to be available for uptake into the roots and shoots of germinating weeds. As a result, some moisture will be required to move the herbicide from the soil surface to the weed/shoot zone for uptake to occur. Typically some rainfall is required for this “activation” process, but the amount varies depending on soil moisture ahead of application, soil type and the chemical characteristics of the herbicide – water solubility and adsorption (Koc factor). The water solubility and adsorption characteristics of herbicides affect the degree of mobility in the soil, its binding to soil colloids (clay and organic matter), and ultimately their uptake into weeds. The University of Hertfordshire pesticide properties database is a good reference for herbicide water solubility and adsorption. Fig 1 below shows the values for some of the most widely used herbicides.

    Fig 1. Mobility and adsorption for common pre-emergence herbicides. Source: University of Hertfordshire pesticide properties database.

    Herbicides with high mobility e.g. metribuzin and dimethanamid-P, are less dependent on rainfall for activation. However with excessive rainfall, herbicides that are even moderately mobile – such as flufenacet and metazachlor – can be lost, leading to poor weed control. Herbicides with moderate-high mobility therefore need “help” to be retained.

    On the other hand, dry soils can be equally problematic particularly for herbicides with very high adsorption, such as pendimethalin, because of the tendency to bind tightly to soil colloids. Herbicides with high or very high adsorption tendencies will be most affected by dry soils and require more moisture to release binding from the soil colloids to become available for uptake into weeds (see Fig 2). 

    Heavy rain threatens crops and groundwater

    To be effective and safe to crops and groundwater, herbicides must bind to soil colloids with only a small amount remaining in solution. With excessive rainfall, herbicides that are even moderately mobile (e.g. metazachlor) can be lost, particularly in light soils, risking crop injury and worse still, movement to groundwater. Increasing retention will help to avoid the risks (see Fig 2).

    Fig 2. Efficacy can be improved by increasing herbicide retention 

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    Protect crops, beat weeds with Backrow

    Backrow is fast becoming a vital performance adjuvant for pre- and peri-emergence herbicides to work at their best. Backrow powers residual herbicides in suboptimal soil and application conditions by reducing drift and by optimising herbicide and moisture retention in the top 5cm of the soil. The resulting improvements in herbicide coverage and uptake into weeds are crucial benefits for growers to protect crops and beat weeds in challenging conditions for the best Autumn start.


    Improves coverage in poor application conditions

    Backrow creates the perfect size droplet for pre- and peri-emergence herbicide applications to work at their best by reducing the number of fine spray droplets prone to drift and by increasing the number of droplets in the optimum size range for better spray coverage of the soil. The addition of Backrow improves herbicide coverage of the soil helping to ensure contact with all germinating weeds.

    Increases herbicide uptake in very dry and very wet soils

    Backrow helps retain moisture in the top 5cm of the soil. With higher soil moisture, more of the herbicide can be available in soil solution and accessible for uptake into weed roots, increasing weed control in dry soils. Backrow also helps to retain herbicides in the top 5cm of the soil, ensuring that in very wet conditions herbicides are still absorbed into the roots and shoots of weeds, instead of being washed below the weed germination zone where uptake would be prevented. 

    Improves safety to crops and groundwater in very wet conditions

    Backrow helps retain herbicides in the top 5cm of the soil, minimising movement down to the seed and emerging shoots, or worse still, leaching to groundwater. This protects crop safety and groundwater in very wet conditions.


    Protect crops, beat weeds with Backrow

    An additional 9.5% control in trials over the last decade

    In Agrii trials over the last 11 years (2009 to 2020), Backrow has improved the control of various grass-weeds by an average of 9.5% – this is the mean of 46 comparisons either pre- or peri-emergence, and with a range of residual herbicides applied in cereals. The highest increases in weed control were achieved in suboptimal conditions.

    Backrow average improvement in grass-weed control over the last decade


    Backrow application technology trials at Agrii

    Watch the video below to find out more about the practical farm scale research conducted by Agrii to put Backrow through its paces, and to really quantify the benefits in suboptimal conditions.

    Download your copy of our Backrow Autumn Product Guide here

      A few of our case studies

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      Require technical assistance or product information? Please get in touch with our Technical Manager, Stuart Sutherland.

      For all other general enquiries, please email or call us at the office. If you’d prefer, drop us a message using our contact form and we’ll get back to you as soon as possible.

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