Article taken from Crop Production Magazine, September 2017.
Pre-emergence and post-emergence residuals play a vital role on many farms. They can take the pressure off contact graminicides, which are often struggling to cope with rising resistance.
With bills approaching £100/ha on some farms for residual herbicides alone, growers need to maximise the best possible performance from their chemistry. Coverage is vital to get the best performance from residual herbicides.
To achieve this, we need to combine higher water volumes and lots of droplets and this can be difficult to achieve together. In order to achieve higher water volumes, traditionally we would switch to a nozzle with a larger orifice which would increase water volume, but also increase droplet size.
There are 64 times as many droplets using a fine spray with a droplet diameter of 100 microns than a coarse one with diameters of 400 microns for the same volume of water. For best performance it is vital to retain a smaller droplet size as well as higher water volume for optimal coverage. There are several ways to achieve both of these simultaneously.
Slowing down forward speed is a simple way to increase water volumes and maintain a smaller droplet size. Whilst this may not be a popular move, it is something that should be considered for difficult grassweed fields.
Using twin lines with the front line angled 30 degrees forward and the back line straight down has been a successful way of achieving best coverage in Agrovista’s application development work in the past. This allows higher water volumes without having to increase droplet size and brings in lateral movement to spray droplets, significantly improving coverage.
A twin cap on each turret can replicate twin line performance for sprayers without twin line capability. As with the twin line set-up, the front nozzle should be angled 30 degrees forward and the back nozzle angled straight down.
The best results for a number of seasons have been with flat fan nozzles angled forwards and down using either twin lines or twin caps.
Using blue 03 nozzles at 3 bar angled forward 30 degrees and straight down in the same turret allows double the water volume whilst maintaining and not compromising spray quality. At 9.6kph that would deliver 300litres per hectare (150 forward & 150 down), and this has consistently produced optimum results.
The following photos show the difference between the best and worst performances from the same product, applied to the same field on the same day using traditional farm equipment, boom heights and forward speeds.
Where 300 l/ha is impractical, the same configuration at 14.4 kph forward speed would deliver approx. 200 l/ha (100 forward & 100 straight down). Whilst this performance is not as good as the higher water volume, it has consistently been the next best and significantly better than air inclusion nozzles.
To complement smaller spray droplets, the closer the nozzle is to the target (while still achieving the correct spray pattern) the better the performance is going to be.
Most spray booms are being carried too high, compromising efficacy and leading to excessive drift. The ideal is to reduce your boom height to around 50cm above the target.
Whilst air inclusion nozzles are very popular and can potentially bring in extra spray days, the performance has been consistently poorer than flat fans. Like with flat fans however, the performance of air inclusion nozzles can be improved significantly by using application aids such as Remix.