Sprayer nozzles - Hit the target

Mark Sandersonin Technical

Syngenta Technical Manager Glenn Kirby explains the science behind sprayer nozzle choice to hit the target.

Syngenta Technical Manager Glenn Kirby with water sensitive paper test

The latest turf protection products are capable of achieving exceptional results. But it is the skills of the sprayer operator and developments in the technology used that can make the crucial difference.

Turf sprayer operators face a number of unique challenges to achieve accurate and consistent results, often whilst under the close appraisal of a critical audience of players and public.

Understanding the fundamentals of the mechanics of spray application, recognising the targets to be hit and the need for effective timing are all key elements of the 'Art of Application'.

Furthermore, today's operator has to be ever more mindful of the essential area of spray stewardship, avoiding problems of waste and minimising risk to the environment.

Sprayer operation involves balancing multiple aims and interacting factors with every application; there is rarely one right solution, particularly with tank mix applications. The key is making a conscious compromise, to aim to get the most important elements of any treatment into the optimum target zone.

Variable parameters for spraying

• Nozzle choice

• Water volume

• Sprayer operation

• Target zone

Spray drift from 04 flat fan on boom (left) compared to 04 XC

Nozzle mechanics

At the point of delivery, nozzle choice has a huge bearing on where the spray will end up.

All nozzles produce an array of droplet sizes; large nozzles tend to produce more large droplets with greater velocity, whilst small nozzles create more small droplets. In general, small droplets are well retained on the leaves of turf grass plants, whilst large solid droplets have a tendency to bounce or roll off.

However, the nozzles' operation has to be understood in tandem with the water volume being applied and the sprayer's operating pressure.

Syngenta research has shown that a large nozzle orifice producing higher proportion of larger droplets, such as an 08, is best for getting sprays down through the turf to reach the soil.

An 04 produces a greater proportion of small to mid-sized droplets that are good for leaf coverage, but some will also reach down to the crown and thatch.

Whilst a smaller nozzle, such as an 025, typically produces a greater proportion of smaller droplets that can be better retained on the leaf, with more effective coverage of the surface.

Water sensitive paper test using, left to right: 025 XC 04 XC and 08 XC nozzles

Using water sensitive paper laid out on sheets on the ground is a really effective way of looking at different nozzle sizes, water volume and operating pressures for individual situations.

One of the issues is that small droplets, with low velocity, are far more susceptible to drift. Targeting tight cut turf surfaces, such as golf greens, is especially challenging since there is very little area or volume to capture and hold the spray; small sub 50 micron droplets can be left suspended in the air, which can then be easily blown away.

Increasing the average droplet size will reduce drift, but if the effect is to move more of the spray down to the thatch and soil, that could be counterproductive for a foliar targeted application, for example. Also, using larger nozzles typically utilises higher water volumes, which can lead to over wetting of the leaf surface and excessive product runoff and loss.

Of course, if your target is the soil for an insecticide or Fairy Ring fungicide treatment, then the larger nozzle, big droplets and higher water volume is exactly the option to reach the desired point.

New technology

Nozzle technology development has seen the advent of air induction (AI) nozzles, using a venturi mechanism to incorporate a bubble of air in each droplet. With this cushioning effect, the larger droplets, less susceptible to drift, still tend to be better retained on the leaf surface, compared to a large solid water drop from a flat fan nozzle.

Utilising this technology and evolving the droplet spectrum, the Syngenta Turf XC Nozzles now produce significantly more droplets per millilitre of spray liquid, compared to other AI or low-drift nozzles tested. This helps to ensure good coverage of the target leaf.

Importantly, tests have shown the 04 XC foliar nozzle, for example, produces less than 3% small sub 100 micron-sized droplets that are highly susceptible to drift, compared to 14% with a traditional flat fan nozzle.

The size of the nozzle orifice primarily dictates the spray water volume, within the parameters of the sprayer speed and the operating pressure.

Raising the operating pressure will also increase the water volume but, as a result, will tend to increase the number of small droplets and therefore the risk of drift, especially with traditional flat fan nozzles.

Syngenta trials have demonstrated that even a small increase in pressure, from three to four bar for example, can dramatically increase the proportion of drifty fine droplets, with some nozzles.

Conversely, reducing the pressure will reduce the driftiness of a nozzle, but can compromise the spray pattern and the velocity of droplets to hit and stick on the target. Most nozzles are designed to work most efficiently at two to three bar.

The effects can be particularly apparent with auto rate controllers. Increasing forward speed automatically increases pressure to maintain a consistent application rate; that will alter the spray droplet pattern, and can inadvertently produce more small droplets susceptible to drift.

The tip is to mark an optimum two to three bar zone on the pressure gauge, and always moderate speed to stay in the zone.

Forward speed also has an effect on the water volume physically applied. Reducing the speed from six to four km/h, for example, will increase the water volume and, therefore, the product application rate. This is a factor to consider when spraying greens, for example, where there is a tendency to slow down at the start and end of each run.

Whilst one nozzle size can deliver different water volumes by adjusting speed and pressure, you can be more efficient and precise in your accurate application of the most appropriate water volume by selecting the most appropriate nozzles size.

Nozzle close ups left to right: 025 XC, 04 XC and 08 XC

Size options

A good selection of nozzles to have available for consistent application in most turf situations, at two to three bar, would be a set of:

• 025 nozzles for greens, delivering a water volume of 200-300 l/ha at four to five km/h - targeting foliar treatments

• 04s applying 220-380 l/ha at five to seven km/hr on fairways for foliar and crown target treatments

• 08s that will deliver 450-770 l/ha at five to seven km/hr for soil target treatments

That is simple if you have a sprayer nozzle holder that accepts three or four bayonet housings, where you can fit the required types and simply twist around to the required nozzle.

If not, it is easier if you buy additional sets of nozzle bayonet holders, which are relatively cheap, and make them up in the workshop with the seals fitted. Store each set in a separate clear plastic box, with the name and size written on the top, and simply swap over the bayonets to change nozzles, rather than the time consuming and messy job of changing individual nozzles.

Always keep a record of the spray output charts for each of your nozzle sets, as these will be invaluable when calibrating the sprayer and establishing the optimum performance for your individual sprayer.

Calibration check

Calibrate your sprayer accurately for each set of nozzles, and check regularly for signs of wear or uneven patterns. Some liquid fertilisers, especially iron, can be especially abrasive and lead to high levels of nozzle wear. Once you get in the routine of checking calibration, it will only take a few minutes.

The rule of thumb is that if any nozzle output is +/- 5% from the average, then change the whole set of nozzles. The cost of nozzles is relatively inexpensive, given the value of treatments being applied, and the importance of getting the best possible results from them.

Machinery maintenance is crucial - including checking tyre pressures, the seals on pumps and valves and inspecting pipes for signs of wear or cracking. An annual National Sprayer Testing Scheme (NSTS) MOT is extremely good practice as a sprayer health check, but needs to backed up with a routine look around the sprayer before every use.

Application Academy

Syngenta's stand at BTME (21-23 January, Harrogate) features a practical demonstration unit to fully explain the fundamentals of spray application - including how to select nozzle types, water volume and sprayer pressure to give the best chance of hitting the target.

Visit the stand to register for a chance to join an unrivalled education opportunity at the pioneering Syngenta Application Academy. Get the opportunity to learn the science behind spray technology from leading industry specialists, along with in-depth practical skills required to become a top sprayer operator.

Application Academy tutorial videos

To watch Glenn Kirby's advice for targeting turf applications visit https://www.greencast.co.uk/syngenta-art-application-videos