Maximize Performance and Consistency

The Science of Spray Application

Spray Perfomance

You know what pesticides you need and when to use them, but what other factors do you need to consider for the best spray performance? Knowing how to achieve the best spray quality can help you maximize profits on your farm.

To be effective, a certain amount of a pesticide must remain on a leaf surface. The deposit pattern depends on the droplet size, spray direction, droplet velocity at the point of impact, physical properties of the spray mixture, and characteristics of the leaf surface.

4 important factors:

Pesticide
Choice

Application Equipment

Application Time

Spray
Quality

The importance of droplet size

Perhaps the single most important factor in spray performance is the droplet size of the pesticide you are using. If the droplets are either too small or too large, efficacy is reduced. The right size droplet can mean a huge difference to your bottom line. Let’s take a look at the reasons behind this.
Too small
<150 microns

The small droplets shown here are below 150 microns in diameter. Small droplets have a low terminal velocity. Their low kinetic energy causes them to decrease speed faster and float longer. Smaller droplets cover more surface area on the plant and have greater droplet density. Without some form of air assistance, however, they can evaporate or drift away from the target, resulting in poorer performance for you and potentially damaging crops in your neighbor’s field.

Too large
>350 microns

The larger droplets that are shown here are above 300 microns and have a high terminal velocity. Their relatively greater mass and higher speed make it easier to manage their trajectory and to reach the target. However, these droplet sizes hit the plant at higher speeds and with greater momentum, which means that they tend to have undesirable aspects of bounce, shatter, and runoff. This reduces their retention on leaf surfaces. If the leaf retains fewer droplets, then the pesticide’s performance is significantly reduced.

One large droplet of 400 microns contains the same volume as 8x 200 micron droplets. Spraying coarse droplets means you often need to increase your water volume to create a sufficient number of droplets.

Large droplets are ideal for spraying pre-emergent herbicides onto bare soil, but they are not suitable for use when spraying fungicides and insecticides where contact is important for product efficacy.

Ideal
150 - 300 microns

For pesticides to work effectively, the target area needs to retain a minimum amount of spray mixture at sufficient concentration for plant uptake. The ideal droplet size for this is 150 – 300 microns. This sweet spot produces droplets that have sufficient momentum to overcome drift and get down to the plant canopy, but they are small enough to stay on the plant surface upon impact.

Even a small change in droplet size from a coarse to a medium droplet will result in a 250% increase in the number of droplets that are sprayed.

Unless a spray droplet properly contacts the leaf surface, pesticide uptake will be minimal.
When droplets are small, more of them can be deposited on a leaf (coverage) and the untreated area between droplets can be decreased (droplet density). Small droplets are also likely to remain on the leaf surface and are less likely to bounce, shatter, or run off. The problem is not many of these droplets will actually reach the target
Larger spray droplets will reach the target but they hit the plant at higher speeds and with greater momentum, which means larger droplets have a greater chance of landing on the ground. And if the leaf retains fewer droplets, then the pesticide’s performance can be significantly reduced
For pesticides to work effectively, the target area needs to retain a minimum amount of spray mixture at sufficient concentration for plant uptake. Generally, this is accomplished using droplets that are between 150 to 300 microns to balance the potential for drift with the potential for good coverage.

Bayer explaining
the importance
of droplet size

The importance of nozzle size

The atomization process that occurs during spraying is based around the shearing of the liquid as it leaves the nozzle into thousands of tiny droplets. Unfortunately, conventional nozzles create a wide range of droplet sizes. Using these type of nozzles are to apply fungicides and insecticides means you will need to significantly increase your water volume to create a sufficient quantity of correctly sized droplets that will be retained on the plant. There is a considerable amount of waste, including time and labor, when applying pesticides this way.
You maybe asking yourself the question ‘So What’

Different Drift Reduction nozzles produce different droplet distribution

Let’s take a closer look at what this means in the field. Different drift reduction nozzles produce different droplet distribution.
Some growers use too coarse a droplet when spraying, in large part because they rely on their rate control system. Growers will often just input their desired gpa and their speed into the controller without considering what droplet will be formed by the nozzle. In some cases low volume cases, this can result in a nozzle pressure of less than 20 psi creating very coarse droplets.
The best practice is to first select the appropriate droplet profile for the pesticide application, then choose desired forward speed and application rate. These criteria should determine the most appropriate nozzle to use.

A key question to ask yourself when filling up your spray tank, is how many gallons of liquid in your tank will actually reach the target and then be retained on the leaf surface.

The importance of application rate

Often growers increase pressure as a way to increase their application rate, but this is actually a counter-productive step. Doubling the pressure only results in a 40% increase in application rate, but it also significantly increases the amount of driftable droplets. For example, some growers use pressures in excess of 150psi for their high value crops and apply application rates of 100-200 gpa. Without some form of air to push the spray into the canopy, though, the spray is not getting into the right area. Why spend your valuable dollars and time to basically wash your plastic?
In practical terms growers are using a wide range of nozzles that are delivering a wide range of droplet sizes. Based upon what we now know, let’s take a closer look at what this means for growers in the field.
A key question that growers should ask themselves when filling up their spray tank, is how many gallons of liquid in my tank will actually reach the target and then be retained on the leaf surface.

How MagrowTec can help?

The physical properties of the spray fluid has a direct impact on the atomisation process at the nozzle and the subsequent droplet profile that is created.
Adjuvants such as drift control agents are often added to the tank mix in order to increase the viscosity of the fluid and make it harder for the fluid to be pulled apart as it exits the nozzle. This results in an increase in the average droplet size of the spray.
Spreading agents are added to lower the surface tension and flatten the spherical spray droplet at the leaf surface, however this can also lead to a decrease in the droplet size during atomisation

The MagrowTec system helps by creating more of the optimum-sized spray – ensuring that more of the spray goes onto the weeds, crop canopy, buds, flowers, stalk, fruit or vegetable product itself or soil, giving better coverage and more protection.

While adjuvants are physical products that are added to the tank mix, the MagrowTec system is a hardware solution that is fitted onto the sprayer itself to condition the fluid as it passes from the tank to the nozzle. The flow of the fluid past static magnetic fields at the appropriate flow conditions changes the physical properties of the spray fluid, creating more of the optimum-sized spray during the atomization process.The conditioned fluid passes through a series of manifolds, containing permanent rare earth magnets similar to those used in electric cars. There are numerous contributing factors, related to the magnetic effect and resultant changes in the physical properties of the fluid delivering the unique spray characteristics and associated benefits. We call this the MagrowTec effect.

The product itself comprises of just two simple components.

The first is a set of 8 aluminum manifolds that are fitted onto the sprayer in between the tank and the section control system. These manifolds can be installed in a single stack of 8 manifolds or in 2 stacks of 4 manifolds making it easy to fit onto any field boom sprayer

The 2nd component is a magnetic rod encased in 304 stainless steel that fits directly into the spray line itself where it is suspended every 20” by a simple spring mechanism.

The product is a completely passive plumbing system with no moving parts or wires and the magnets only lose 1% of their total strength over 15 years.

The kit can be installed onto a sprayer by 2 people in around 6 hours and can be removed in around 1 hour meaning that it can be easily transferred onto a new sprayer when you’re trading in your sprayer.

The product is modular and so if your new sprayer has a longer boom you only need to purchase some extra rods for your spray line.

There is virtually no configuration or maintenance required. Each manifold only holds 0.5 gallons (2 litres) and so regular flushing practices between sprays is sufficient.

Each rod only weighs 1.5 lbs and so the added weight on a 120’ sprayer is only 110lbs across the entire boom.

MagrowTec Benefits

As we have discussed earlier, improving your Spray Quality is really important as it enables you to deliver more of your important pesticide onto the intended target, while at the same time reducing negative effects of drift into neighbours fields and run-off into the soil. Improving the spray quality enables the grower to have more options at their disposal.

They can use a 20-30% lower application rate with the MagrowTec system to achieve the same coverage as their regular sprayer.

They can use their current application rate and deliver increased coverage to improve the efficacy of their pesticide application.
They can reduce their application rate, while also increasing coverage and efficacy