With the loss of diquat from the weed control toolbox this spring, potato growers are likely to be under even greater pressure to ensure residual herbicide sprays are both timely and effective, particularly as soils start to dry out across the country.
Up until now, weed control has been pretty straight forward – plant and wait for weeds to emerge and then apply a residual + diquat tank-mix. This simple treatment was pretty effective, with a low risk of crop damage. However, whilst Gozai (pyraflufen-ethyl) and Shark (carfentrazone ethyl) remain good alternatives to diquat for contact activity, they do pose crop safety risks where applications are made post crop emergence.
Now more than ever, it will be vital to achieve the best weed control possible with residuals pre-emergence by limiting the impact of sub-optimal spraying and soil conditions on herbicide application.
This is where residual herbicide adjuvant Backrow, could be a vital addition, believes Stuart Sutherland, technical manager for Interagro. “Backrow is a tried and trusted adjuvant, proven to optimise the performance of residual herbicides in less-than-perfect conditions, whilst also protecting crop safety”.
Residual herbicide performance depends on good application conditions and sufficient uptake in soil water by the roots and shoots of germinating weeds. However, cloddy tilths and spray drift can both lead to poor coverage, preventing herbicide contact with germinating weeds. Weeds that do not come into contact with the herbicide at germination will emerge, putting pressure on the need for follow-up contact treatments.
Adding Backrow can help, explains Mr. Sutherland. “Backrow creates the perfect size droplet for pre-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. It’s worth noting that there is more soil to spray in one hectare of potatoes than one hectare of wheat due to the potato ridges, so the rates of herbicides being used need to work even harder”.
“Residual herbicides also require moist soils to work well, whilst on the flip side, excessive rainfall or heavy early irrigation on light or stony soils can move herbicides to the potato sets and damage the crop.
“Perhaps of greater benefit to growers right now, given the dry soils, Backrow will help 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, particularly important for herbicides such as pendimethalin, prosulfocarb and new herbicide aclonifen which are less effective in dry soils.”
“Where excessive moisture is a threat, Backrow will help by retaining herbicides in the top 5cm of the soil. This increases the availability of herbicides for uptake into weeds and prevents the movement of herbicide to the crop root zone, reducing the threat of crop phytotoxicity. This is particularly useful for herbicides which are more “mobile” such as metribuzin”.
Replicated field trials have consistently demonstrated improved weed control from the addition of Backrow to residual herbicide chemistry, with an additional 8% against weeds such as annual meadow-grass. Weed control trials conducted with Scottish Agronomy in 2019 also showed improved weed control with Defy + Praxim, Shotput + Praxim, and Shotput + Emerger.
To see our Backrow trials results in potatoes and for more info please visit: https://bit.ly/3aOTC81