Taken from Agronomist & Arable Farmer, March 2017
Few larger sprayers, particularly those with booms of 36m or more, are capable of spraying at 50cm above the leaf target, the ideal height to minimise drift and maximise spray deposition.
A realistic minimum height for most practical situations is 80cm, and many operators go higher to ensure the boom maintains sufficient clearance above the crop.
""While additional drift is obvious as boom height increases, few operators realise the figures involved," says Agrovista technical manager Mark Palmer.
""Raising the boom from 50cm to 1m typically increases drift potential by 10 times for a standard flat fan nozzle, and by four times for an air induction nozzle.
""These amounts of drift can reduce spray efficacy significantly," says Dr Palmer.
Trials have shown the best way to overcome this is to use air induction nozzles, and to add the adjuvant Velocity, a combination of fatty acid methyl esters, organosilicones and humectants that provides drift control and acts as a very efficient wetter and spreader once the spray hits the target. Drift tends to be the limiting factor when using flat fan nozzles, so air inductions have grown in popularity as they reduce drift and allow more application days. However, efficacy can be compromised as coverage suffers.
""Adding Velocity improves coverage of the leaf surface, which, in turn, improves disease control and increases yield," says Dr Palmer.
Using a fungicide alone means droplets are prone to bouncing off the leaf. They tend to have a high surface tension which reduces coverage, and uptake through the waxy leaf cuticle is relatively poor.
""Adding Velocity to the spray solution reduces droplet bounce and results in a more even distribution across the leaf. This improves uptake through the cuticle and allows rapid uptake through the stomatal pores.""
To assess the performance of Velocity under farm conditions, Dr Palmer carried out 24 trials over seven seasons, using a range of triazole/SDHI combinations with and without strobilurins. The fungicides were applied at GS39, using a water volume of 100 litres per hectare through air inclusion nozzles at 14.4kph, to mimic farm practice. On average, adding Velocity increased yield by 0.45 tonnes/ha across the trials. With wheat at £130/t, that represents a 15-to-one return on input, he adds.
""In most situations and most seasons that combination of speed and 1001/ha water volume plus Velocity, delivers perfectly acceptable results in terms of disease control when using air induction nozzles," says Dr Palmer. ""Occasionally, if you get yellow rust established in the crop you may need to increase water volume to 2001/ha to penetrate the canopy.
""However, in general we found 1001/ha delivered better results. It produces smaller droplets that deliver a higher concentration of spray solution to a given leaf area, which gets into the leaf more quickly. Timeliness also improves by around a third when spraying at 1001/ha compared with 2001/ha.""
The results suggest significant gains are likely in farm spray programmes, says Dr Palmer.
""Operators are travelling faster and increasingly switching to air induction nozzles to improve output, and the benefits are really starting to stack up.""
Other work on late-season sprays has shown that nozzle configuration can further improve control. In nine trials across Europe, using a fungicide alone gave just over 50% control of fusarium. Adding Velocity increased control to 65%, but applying the fungicide/Velocity mixture through a forward angled nozzle boosted control to 82% on average.
This was probably due to better coverage of the ear, which presents a tricky vertical target for the standard vertical nozzle configuration, says Dr Palmer.
Further work will investigate the use of twin-capped nozzles providing two forward-angled sprays angled at eight degrees and 30 degrees. ""This mimics a twin-line sprayer, and by applying 2001/ha we can deliver many more droplets, which greatly improves coverage and efficacy. We have achieved excellent results using this technique with autumn herbicides, so are now looking to see if we can get similar benefits with fungicides.""