Spray Application Technology: Selecting Spray Nozzles with Drift-Reducing Technology

Consider your priorities before making nozzle choices. Nozzles are relatively inexpensive, but they can be the most critical part of your spray system.

• What droplet sizes, aka spray quality, do your nozzles need to produce?
• What water volumes do your nozzles need to produce?
• At what ground speeds do you plan to run your sprayer?
• Are you planning to spray a dicamba formulation or 2,4-D formulation that is subject to Environmental Protection Agency (EPA) requirements for over-the-top applications to soybean?
• How many sets of nozzles are you willing to buy?

Among pesticide types commonly used in postemergence foliar applications, systemic herbicides generally require the lowest application volumes and allow for the largest droplet sizes (coarse to very coarse spray quality).

Contact herbicides require comparatively higher application volumes, along with medium to coarse spray quality.

Insecticides and fungicides generally require fine to medium spray quality and similar or higher application volumes as contact herbicides.

Over-the-top dicamba applications to crops with the dicamba-tolerant trait require nozzle configurations that supply extremely coarse or ultra coarse spray quality.

No one nozzle will be ideal for all of the pesticide application needs outlined above. Consider the application protocols necessary to maximize the efficacy of your crop protection products, then choose a set of nozzles accordingly.

abels for these products specify that they may only be applied using the nozzles and operating pressures listed on the product websites. As of this writing, just three of the 15 nozzle models featured in this publication’s illustrative nozzle set may be used for applying dicamba: the Air Induction TeeJet, Turbo TeeJet Induction and Hypro Ultra Lo-Drift. In contrast, seven of these nozzle models may be used to apply Enlist One or Enlist Duo. They are the Billericay Air Bubble Jet, Greenleaf AirMix, Greenleaf TurboDrop XL, Hypro Ultra Lo-Drift, Air Induction TeeJet, AIXR TeeJet and Turbo TeeJet. Always reference the latest pesticide labels for information on allowable spray nozzles.

The approved nozzle tip and operating pressure combinations will generate an extremely coarse or ultra coarse spray quality (Table 1).

Let us consider two nozzles as examples of the ASABE S572.3 classification system (Figure 1). The ISO F 110 02 and ISO Injet 02 are flat-fan type nozzles manufactured by Hardi. When operated under identical conditions, 44 pounds per square inch (psi) operating pressure and 0.21 gallons per minute (gpm), they produced the droplet size distributions displayed in the lower panels of Figure 1. Corresponding illustrations of the droplet size distributions using common household objects are in the upper panels of Figure 1.

Table 1. Approximate Dv0.1, Dv0.5 and Dv0.9 droplet size limits for spray quality categories defined in ASABE S572.3, and comparative descriptions of droplets ranging in size from fog to thunderstorm rain.

Photo Credit:

Graphs created by Proulx using the experimental data of Nuyttens et al. (2007). Jars created by Proulx

Distributions of spray volume fraction by droplet size, expressed graphically and illustrated by jars filled with common household objects. Spray quality classifications of fine (F) and coarse (C) are according to ASABE S572.3, for sprays produced by a Hardi ISO F 110 02 spray nozzle at 44 psi and a Hardi ISO Injet 02 spray nozzle at 44 psi.

With Dv0.1, Dv0.5 and Dv0.9 values of 113, 214 and 344 microns, respectively, the ISO F 110 02 nozzle at 44 psi produces a fine (F) spray quality. Approximately 60% its spray volume consists of droplets with sizes from 100 to 250 microns, similar in size to a fine mist or fine drizzle, and approximately 20% of its spray volume consists of drift-prone droplets sized 150 microns or smaller. In contrast, less than 5% of its spray volume is found in droplets with sizes of 500 microns or larger.

In contrast, the ISO Injet 02 nozzle has air induction drift-reducing technology (see the Drift-Reducing Nozzle Technologies section). With Dv0.1, Dv0.5 and Dv0.9 values of 282, 507 and 645 microns, respectively, this nozzle produces a coarse (C) spray quality when operated at 44 psi. Only 6% of its spray volume is found in droplets of 100 to 250 microns, with less than 2% of its volume consisting of drift-prone droplets sized 150 microns or smaller. However, this nozzle produces approximately 50% of its volume in droplets with sizes of 500 microns or larger, including approximately 25% of its volume in droplets sized 600 microns or larger. Droplets of this size could be considered prone to bouncing off target plants, especially if produced by a standard hydraulic nozzle, but air induction nozzles seem to more effectively deposit these large droplets on the target. This is most likely due to the reduced exit velocity of droplets from an air induction nozzle, which results from pressure drop at the exit orifice.

ASABE S572.3 is the latest update to the ASABE droplet size classification standard and was published in February 2020. As of this writing, most nozzle manufacturer catalogs display spray quality classifications according to ASABE S572.1, which was published in March 2009.

Compared to S572.1, S572.3 decreased the reference operating pressure and flow rate for the nozzles defining the C/VC, VC/XC and XC/UC spray quality thresholds. This effectively increased the droplet sizes of the Dv0.1, Dv0.5 and Dv0.9 that define these thresholds, meaning that nozzle spray qualities rating as VC, XC, or UC according to S572.1 could shift into the next finer category under S572.3 (C, VC and XC, respectively). S572.3 also flipped the colors used to define coarse and very coarse spray qualities to make ASABE S572.3 fully equivalent to the International Organization for Standardization (ISO) 25358:2018 droplet size classification standard.

The changes implemented in S572.3 should not greatly impact nozzle selection decisions for pesticide applications. However, keep in mind that spray quality reported across manufacturer catalogs may be defined by different standards and that spray quality reported by a nozzle catalog may be defined by a different standard than spray quality reported in other reference materials, such as a pesticide label.

Extended-range flat fan nozzles were historically considered the standard nozzle for many pesticide applications in the northern Plains. Variations of this standard hydraulic design, where liquid is drawn in through an inlet and atomized through an exit orifice (Figure 4), are still available from several manufacturers.

The design is available in a wide range of flow rates and fan angles to fit many application needs. These nozzles produce a uniform spray pattern when patterns are overlapped 30% to 50% and when operated at 15 to 60 psi.

Spray quality is fine to medium for small nozzles (0.4 gpm and lesser). Larger nozzles (0.5 to 0.8 gpm) will produce medium to very coarse spray quality. At any nozzle size, higher pressures (above 30 to 40 psi) will produce a greater proportion of drift-prone droplets.

At any given flow rate and pressure, an extended-range flat fan nozzle with an 80-degree discharge angle will produce slightly larger droplets than a comparable 110-degree nozzle.

Pre-orifice nozzles feature an internal turbulence chamber between the liquid inlet and the exit orifice (Figure 4). The turbulence chamber absorbs energy from the incoming liquid stream, reducing exit pressure from the nozzle. This creates larger droplets and a more uniform spray distribution, resulting in fewer drift-prone droplets.

The Hypro Guardian and Turbo TeeJet are examples of nozzles featuring the pre-orifice turbulence chamber drift-reducing technology.

Both nozzles produce a wide, uniform spray pattern with a slight inclination, which allows the spray to be directed slightly forward or backward. These nozzles can also be operated over wide pressure ranges (Table 2). This makes them well-suited for use with automatic rate controllers that use pressure to adjust the flow rate in response to a change in travel speed.

When operated at pressures near the middle of their manufacturer-authorized ranges, commonly used nozzle tip sizes will produce medium to very coarse spray quality (Table 3). The spray qualities produced by these nozzles are most suitable for postemergence applications of contact herbicides, where adequate herbicide efficacy requires greater spray coverage compared to systemic herbicides. Pre-orifice nozzles such as these are generally better suited for contact herbicide applications than are air induction nozzles, as pre-orifice nozzles tend to produce relatively finer spray qualities than many of the air induction nozzles (Table 2, Figure 7).

Among the air induction nozzles in the example set, the Greenleaf AirMix, Hypro GuardianAIR, Greenleaf TurboDrop XL, Lechler IDK and Hypro Ultra Lo-Drift nozzles are collectively capable of producing fine or medium spray qualities, in addition to the coarser spray qualities more typically associated with air induction nozzles (Tables 2 and 3). These nozzles are well suited for the application of soil residual and postemergence systemic herbicides and are also acceptable for contact herbicide applications (Table 3).

All other air induction nozzles are not rated to produce medium or finer spray qualities when using typical nozzle tip sizes operated at pressures near the middle of their manufacturer-authorized ranges (Tables 2 and 3). The Billericay Air Bubble Jet, AIXR TeeJet and Hypro AVI nozzles produce coarse to extremely coarse spray qualities, while the Hardi Injet, Air Induction TeeJet, Delavan Raindrop Ultra and Turbo TeeJet Induction nozzles produce only very coarse or coarser spray qualities. While these nozzles are well suited for applying soil residual and postemergence systemic herbicides, they are not recommended for applying contact herbicides (Table 3).

Figure 7 illustrates the variation in spray quality produced by the example air induction nozzles when holding water volume constant at 8 gpa. Note that the observed spray quality does not always match the reference spray quality taken from manufacturer catalogs, as the method used to measure spray quality (analysis of water-sensitive paper) is much less precise than the method manufacturers use to measure nozzle spray quality (measurement with a laser-based instrument).

The example air induction nozzles also differ in their design features (Table 4). Several nozzles offer an optional ceramic pre-orifice or exit orifice, which provides high wear resistance compared to polymer. Most nozzles feature a two-piece design where the pre-orifice is removable without requiring any special tools, which eases cleaning, but some nozzles require a needle-nosed pliers to remove the pre-orifice. Due to their wider nozzle body, certain nozzles require a specialized nozzle cap for attachment to the sprayer boom. However, most nozzles fit a standard Spraying Systems Quick TeeJet nozzle cap or feature an integrated cap with an identical fitment.

Table 4. Design features of air induction nozzles.

Whether featuring a pre-orifice or air induction design, drift-reducing nozzle tips result in an internal pressure drop within the tip body and reduced operating pressure at the exit orifice. Due to this design, drift-reducing nozzle tips require greater operating pressures than standard hydraulic nozzles.

Check the operating pressure of your sprayer and the ability of your pump to supply the higher pressures necessary for these drift-reducing nozzles. If your spray system has trouble exceeding 60 psi, consider replacing the pump or using a nozzle that produces a desirable droplet size at lower pressures.

Pressure loss across the length of the boom may cause variation in the discharge from nozzles so check operating pressure along the boom to ensure it is uniform and at the nozzle manufacturer’s minimum pressure. When using an automatic flow regulator, watch boom pressure and sprayer output closely when changing speeds. Poor spray patterns are often the primary reason for performance complaints.

While operating pressure and nozzle design are the primary determinants of droplet size, the primary determinants of spray pattern and coverage are spray fan angle, nozzle spacing on the boom and boom height. Most fan-pattern nozzle tips feature spray fan angles from 80 to 120 degrees (Table 2). North American sprayers typically feature 20-inch nozzle spacing, and nozzle catalogs typically specify the proper boom height for their nozzles at this spacing. The optimum boom heights are usually configured to supply a recommended 100% spray overlap for fan-pattern nozzles, meaning that the edges of a nozzle’s spray should align directly underneath the adjacent nozzles on the boom.

A proper spray angle is critical to achieving the recommended spray overlap and coverage. Therefore, understand that the spray angle does not remain constant with changes in operating pressure, as a decrease in pressure causes the spray angle to narrow. This is of particular concern with air induction nozzles.

Although many air induction nozzles are sold as 110-degree fan angles, their spray pattern sometimes is closer to 80 degrees and quickly becomes narrower at lower pressures. This is because the exit orifice has a greater flow rate than the metering orifice, causing a significant pressure drop at the exit orifice, which narrows patterns. Even at a gauge pressure of 80 psi, the exit tip pressure may be only 20 to 40 psi. Watch patterns carefully and set your boom at the height needed to achieve proper overlap.

Even though manufacturers may rate air induction nozzles to operate over a wide pressure range, this does not mean that the spray angle remains constant. Aim to operate your nozzles near the middle of their rated pressure range, and be aware that spray pattern breakdown may occur when air induction nozzles are operated at pressures less than 30 psi. Lower pressures are of greater concern than higher pressures in terms of maintaining proper spray patterns.

In a flow-based control system, which is traditional for agricultural sprayers, a sprayer controller adjusts operating pressure in response to variations in ground speed. This maintains a constant application rate. In contrast, pulse width modulation (PWM) sprayers provide independent control over nozzle pressure and flow rate. This is done by using a rapidly pulsing solenoid within each nozzle body to vary the amount of time spray is flowing to the nozzle.

Operating pressure does not change with travel speed on a PWM sprayer. Drift-reduction benefits come from using larger orifice nozzles to produce larger droplets at lower pressures while varying the application rate by varying the duty cycle of the solenoid.

Nozzles with pre-orifice drift-reducing technology are compatible with PWM sprayers. Air induction nozzles have traditionally been considered incompatible with PWM sprayers, as these designs can leak during the brief off-cycle. This causes an internal pressure drop within the nozzle, which must be replenished during the next on-cycle, which then affects pattern development and droplet atomization.

However, nozzle manufacturers recently have begun to publicize certain air induction nozzles as compatible with PWM sprayers. Proceed with caution and seek documentation of this compatibility before using air induction nozzles on a PWM sprayer.

Most air induction nozzles feature polymer (i.e., plastic) construction. Polymer has very good wear characteristics and can sometimes outlast stainless steel. However, polymer is prone to deformation if cleaned with hard objects such as fine wire or a knife tip. Use only a soft-bristled brush, such as a nozzle-cleaning brush or a toothbrush, to clean polymer tips.

Nozzles occasionally plug, even with clean water and screens. However, an air induction nozzle should present fewer plugging problems than standard hydraulic nozzles because the metering orifice is round, allowing larger particles to pass through. Also, the exit orifice typically has about twice the flow rate of the metering orifice, further reducing the likelihood of plugging.

If the exit orifice of an air induction nozzle plugs, the nozzle must be taken apart for cleaning. Air induction nozzles sometimes are difficult to disassemble, especially in the field, and nozzle parts can be easily lost. Your best option may be to carry extra nozzles and disassemble and clean the plugged ones at the shop, where you have access to compressed air and water.

Some adjuvants are marketed to improve spray deposition on intended targets and reduce spray drift. Some viscositymodifying, drift-reducing adjuvants should not be used with air induction tips because the adjuvant may interfere with proper spray atomization and droplet formation. Always read the pesticide and adjuvant labels for restrictions before use and check your spray pattern after adding any adjuvant.

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This publication was previously titled ‘Selecting Drift-Reducing Nozzles’ and ‘Selecting Spray Nozzles to Reduce Particle Drift’. Vern Hofman, Professor Emeritus, Department of Agricultural and Biosystems Engineering, North Dakota State University authored the original publication. James Wilson, Pesticide Training Coordinator (retired), South Dakota State University, and John Nowatzki, Agricultural Machine Systems Specialist (retired), North Dakota State University Extension provided subsequent revisions.