As the busy June-July demo season draws to an end prior to combines rolling, there have been some key lessons to learn from a very difficult season.
One of the most important for me has been the importance of correct application. The differences between good and poor application techniques have been clearly noticeable in trials at demonstration sites but have been even more pronounced on a farm scale this season, particularly in areas with high grass-weed problems or fields with high disease pressure.
As we start to consider residual herbicide programmes for the coming autumn, it is a good time to set up your sprayer to ensure it will give the best performance, as it is very clear the performance from the same products applied on neighbouring farms at the same time have varied dramatically from excellent to disappointing control depending on the application technique used.
The difference in performance from residual grass-weed herbicides has been clear all season, and it is very evident to get the best performance from residual herbicides, we need to ‘paint’ the soil. To achieve this we need to combine both higher water volumes and lots of droplets. This achieves much more even coverage rather than relying on big droplets spreading out. These two traits can be difficult to achieve together as traditionally in order to achieve higher water volumes, we would switch to a nozzle with a larger orifice, which would obviously increase water volume, but also at a cost of increasing droplet size.
You have 64 times as many droplets using a finer spray with a droplet diameter of about 100 microns than a coarser one with droplet diameters of about 400 microns for the same volume of water so 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 these traits simultaneously. Using twin lines with the front line angled 30 degrees forward and the back line straight down has been the most successful way of achieving this in Agrovista’s application development work over the past few seasons.
A further simple way to increase water volumes while maintaining a smaller droplet size is to reduce forward speed. For example, using an 03 flat fan blue nozzle at its sweet spot operating pressure of 3 bar would deliver an application volume of about 100 litres/hectare at 14kph. By reducing forward speed to 8kph, application volume would increase to around 180 litres/ha while still maintaining the same droplet size. This may not be popular move for large acreages, but it is something we should consider for individual difficult grass-weed fields.
To improve performance from single lines, bringing in lateral movement to spray droplets by alternatively alternating every second nozzle forward 30 degrees with every other nozzle straight down (not backwards) will significantly improve coverage and lead to better performance.
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 and one of the biggest problems these days is that with wider booms and increased forward speeds, the opposite is happening as most spray booms are being carried too high, compromising efficacy and leading to excessive drift. If you can reduce your boom height to about 40-50cm above the target, that’s a real step in the right direction.
Low drift nozzles do still have a role to play as they can bring more spray days into play, however due to their coarser spray quality, it is essential they are used in conjunction with an application aid to help improve coverage and absorption onto the target.