Article taken from Agronomist & Arable Farmer, September 2017.
With bills exceeding £100/ha on some herbicides alone, growers need to eke out the best possible performance from their residual chemistry.
""It's very evident that to get the best performance from residual herbicides, we need to 'paint' the soil," said Agrovista technical manager Chris Martin. ""To achieve this, we need to combine higher water volumes and lots of droplets.
""A fine spray with a droplet diameter of around 100 microns will produce 64 times as many droplets than a coarse one with 400 micron droplets for the same volume of water.""
Slowing down forward speed is a simple way to increase water volumes while maintaining a smaller droplet size. Although this might not suit large acreages, it should be considered for difficult grass weed fields, said Mr Martin.
Using twin lines with the front line angled 30 degrees forward and the back line straight down is more practical and has achieved best coverage in Agrovista's comprehensive application development work over the past few seasons.
For sprayers without twin line capability, this performance can be replicated by using a twin cap on each turret, angled forward 30 degrees and straight down.
""Using blue 03 nozzles at 3 bar at 9.6kph would deliver about 300 litres/ha, and this has consistently produced the best results," Mr Martin commented.
The same configuration at 14.4kph would deliver about 200 I/ha.
Most spray booms are being carried too high, compromising efficacy and leading to excessive drift. He said: ""If you can reduce your boom height to around 40-S0cm above the target, that's a real step in the right direction.
""A further important component to maximise preÂem efficacy is a high quality application aid. Remix, a paraffinic oil made up of long chain molecules designed to reduce spray drift, can have a dramatic effect when using fat fans, and even more so with air inclusion nozzles.
""Remix improves the spray pattern, giving a more even distribution of herbicide onto the soil," Mr Martin added. ""Its long-chain molecules give it a positive charge, which helps to bind the herbicide active to clay and organic matter, keeping herbicide in the surface layer for longer, improving efficacy of the residual herbicides.""
This helps reduce crop damage by reducing the amount of chemical being washed down to emerging seedlings - an increasing problem as more and more residual pre-em chemistry is stacked. This can be further exacerbated with poor seed beds and/or heavy rain soon after application.
Trials in 2016/17 at Draughton, Northants, where levels of difficult-to-control black-grass reach 650 heads/sq m, confirmed several years' results in trials, and in the field, that show how effective Remix can be.
Three large plots of wheat received varying pre-em approaches. One was left untreated, the second received Liberator at 0.61/ha plus an alternative adjuvant at 0.21/ ha, while the third received the same dose of Liberator plus Remix at 0.21/ha.
Early post-em regimes were then overlaid on these plots (see graph). One section received nil treatment, another Avadex (15kg/ha) + Fence (0.251/ha) + Herold (0.31/ha) and the final section received the same, plus Xerton (0.61/ha).
""The left-hand bars demonstrate the black-grass pressure at Draughton and the importance of including flufenacet as the base for black-grass control," said Mr Martin. ""The second and third set show how a comprehensive stack can aid performance, and how Remix can maximise the improvement. The results show that good application technique and keeping residual chemistry near the surface is at least as important as increased residual loading.""