Spring forward with Backrow for a weed free start

Spring has finally sprung, and with it, pressure on growers to get spring crops in the ground and off to a weed free start in order to maximise yield and profitability. Working against the clock, to remove the threats posed by lack of soil moisture and germinating grass / broad leaf weeds, optimising the performance of residual herbicides pre- and peri-emergence, will be vital.  

Backrow is a tried and trusted adjuvant, proven to optimise the performance of residual herbicides in less-than-perfect conditions, whilst also protecting crops and groundwater, free from weed competition.

Requirements for effective weed control pre-/peri-emergence

Residual herbicide performance depends on good application conditions and sufficient uptake in soil water by the roots and shoots of germinating weeds (Fig 1). Cloddy soils, spray drift, dry soils, excessive moisture and excessive herbicide adsorption to soil organic matter, can all reduce herbicide:weed contact. Weeds that do not come into contact with the herbicide at germination will emerge and potentially thrive, putting pressure on treatments post-emergence.

Fig 1. Herbicide dissolved in soil water is taken up by the roots of weeds

Why can residual herbicide performance be improved?

Understanding the interaction between soil, herbicide and soil moisture can go a long way to understanding performance limitations and how herbicide performance can be improved. 

Poor coverage

The performance of residual herbicides is heavily reliant on good coverage across the soil surface to ensure good 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, thereby escaping control.

Poor herbicide uptake

For success, residual herbicides must be dissolved in soil water and be in a position in the soil to be absorbed. For most arable weeds, that’s the top 5cm of the soil because this is the depth at which most weeds will germinate from. As a result, some rainfall will be required to move the herbicide from the soil surface to the weed root and shoot zone for uptake to occur. Typically some rainfall is required to activate the herbicide, but the amount varies depending on soil moisture ahead of application, and soil type.

To be effective and safe to crops and groundwater, herbicides must bind to soil colloids (clay, OM) with only a small amount remaining in solution. This avoids leaching from the weed germination zone down through the soil profile. The mobility/adsorption tendency of herbicides is however, herbicide specific. Herbicides with high mobility e.g. metribuzin, dimethanimid-P, clomazone, are less dependent on rainfall for activation. However, with excessive rainfall, herbicides that are even moderately mobile can be lost, leading to poor weed control and threats to crop safety and groundwater. Herbicides with moderate to high mobility therefore need “help” to be retained. The level of herbicide in solution is directly related to soil moisture content, and whilst too much moisture can cause herbicide leaching, too little can be equally problematic. Poor weed control typically occurs in dry soils as less herbicide is in soil water, and this is an issue particularly with herbicides that have a high adsorption tendency, such pendimethalin, aclonifen, and prosulfocarb. 

Herbicide adsorption to soil colloids is the biggest factor influencing herbicide availability and efficacy. The degree of herbicide adsorption to soil colloids in any particular soil is affected by the soil’s cation exchange capacity (CEC) – the number of adsorptive sites. It is influenced by the soil’s clay and organic matter content e.g. pure sand has 1-5 sites, loam 5-15.

Understanding  herbicide water solubility and adsorption is key to identifying performance limitations of particular herbicides. Download our Training Guide below for information on specific herbicides.

How Backrow can help

Approved for use in a wide range of spring and winter-sown crops including barley, beans, potatoes, veg and cereals, Backrow optimises herbicide and moisture placement in the soil, increasing herbicide coverage, uptake and crop safety.

Backrow improves coverage

Backrow creates the perfect size droplet for pre- and peri-emergence herbicide applications 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.

Backrow improves herbicide uptake and crop safety

Backrow helps retain herbicides in the top 5cm of the soil. This increases the availability of herbicides for uptake into weeds (given sufficient moisture) and prevents the movement of herbicide to the crop root zone, reducing the threat of crop phytotoxicity and leaching to groundwater. 

Backrow also helps retain moisture in the top 5cm of the soil in dry conditions. With higher soil moisture, more of the herbicide can be available in soil solution and accessible for uptake into weeds. 

For a weed free start

Backrow has been well proven in a very wide range of crops, with a broad range  of herbicides over the last 10 years, delivering an average improvement in black-grass control of 9% across 47 replicated trials. In suboptimal conditions, such as dry soils, weed control has been improved even further. 

Backrow is recommended with all pre- and peri-emergence herbicides, particularly where application and soil conditions are suboptimal. Safe and effective in all soil types, Backrow is the ideal herbicide partner for a weed free start this spring. 

Advantages of Backrow

• More effective weed control in suboptimal soil and application conditions
• Prevents the leaching of plant protection products to groundwater, providing a valuable stewardship measure
• Effective in all soil types except pure sand – some organic matter required to bind to