2.3 Minimizing Pesticide Drift

Spray drift of pesticides is an important and costly problem facing pesticide applicators. Drift can result in damage to susceptible off-target crops, environmental contamination to watercourses and a lower than intended rate to the turfgrass, thus reducing the effectiveness of the pesticide.

 

There are two types of drift, airborne drift, often very noticeable and vapor drift. The amount of vapor drift will depend upon atmospheric conditions such as humidity, temperature and the product being applied and can occur days after an application is made. Drift is influenced by many inter-related factors including droplet size, nozzle type and size, sprayer design, weather conditions and last but not least the operator.

 

2.3.1 Droplet Size

Lower spray volumes can result in smaller droplets that enhance leaf coverage although there is a limit to droplet size due to drift. Droplets under 150 microns generally pose the greatest hazard; droplets less than 50 microns have insufficient momentum for impaction as they remain suspended in the air indefinitely or until they evaporate. Research in England concluded that a 100 micron droplet takes 11 seconds approximately to fall ten feet in still air; when a similar size droplet is released into a 5mph wind it will drift about 75 feet before hitting the ground.

 

The higher the operating pressure, the smaller the droplet. Conversely, low pressure produces large droplets that may bounce off the target. Certain spray surfactants can change the droplet spectrum, reducing the number of driftable droplets.

 

2.3.2 Nozzle Type and Size

Correct nozzle selection is one of the most important yet inexpensive aspects of pesticide application. A nozzle’s droplet size spectrum determines deposition and drift.

 

Conventional flat fan nozzles fitted to a turfgrass sprayer produces droplets in the range of 10 – 450 microns. There are 25,000 microns in one inch. Drift is a concern with droplets less than 100 microns.

 

Increasing the Volume Median Diameter (VMD) will certainly reduce drift, but too large a droplet will bounce off the leaves to the ground.

 

Conventional flat fan nozzles

Nozzles with 80 degree angle produce coarser droplets than 110˚ at the same flow rate but 80˚ nozzles require the boom to be set at 17-19 inches;  110˚ nozzles can be set lower at 15-18 inches above the target. (The lower the boom, the less chance of drift). Spray quality is fine – medium at 15 - 60 psi.

 

Pre-orifice flat fan nozzles

The internal design of this nozzle reduces the internal operating pressure compared to a conventional flat fan resulting in coarser droplets (high pressure creates fine droplets, low pressure creates coarser droplets). Available as 80˚ or 110˚ nozzles. Spray quality is medium - coarse at 30- 60 psi. Drift-guard is a well-known trade name.

 

Turbo-teejet

A turbulence chamber produces a wide angle flat spray pattern of 150˚. Spray quality is medium – coarse at 15- 90 psi. Nozzles can be set at 15-18 inches above the target.

 

Turbo-Turfjet

This nozzle produces a very coarse droplet, ideal for liquid fertilizers. This nozzle works at pressures up to 75 psi and can be set at 20 – 40 inch nozzle spacing.

 

Air induction nozzles

Air induction, air inclusion or venturi nozzles are flat fan nozzles where an internal venturi creates negative pressure inside the nozzle body. Air is drawn into the nozzle through two holes in the nozzle side, mixing with the spray liquid. The emitted spray contains large droplets filled with air bubbles (similar to a candy malt ball) and virtually no fine, drift-prone droplets. The droplets explode on impact with leaves and produce similar coverage to conventional, finer sprays.

 

Air induction nozzles reduce drift even at higher pressures of 80-90 psi. They are only available at 110˚ fan angles so boom height may need to be adjusted to 15-18 inches.

 

The use of adjuvants will certainly help create bubbles and trials in the USA and Europe confirm this.

Air induction nozzles are more expensive than a conventional flat fan tip, although field results show greatly reduced drift and improved product deposition.

 

Manufacturers of air induction nozzles include:

 

Greenleaf TurboDrop nozzles consist of two primary components - the venturi air aspirator and the exit pattern tip. A ceramic orifice in the venturi determines the flow rate of the complete assembly. The venturi is ISO color coded to designate flow rate. The exit pattern tip does not affect flow rate: it is only used to form the desired spray pattern. Pressure range is 40-120 psi.

 

Spraying Systems Tee Jet Air Induction (AI) comprises a plastic body with a steel tip, rated for 30 to 100 psi. They are plastic, single-piece construction.

 

Hardi ID air induction is similar in construction to Spraying Systems AI nozzle; it is a one piece plastic nozzle.

Albuz is similar in construction to Spraying Systems AI nozzle; it is a one piece plastic nozzle with a ceramic tip.

 

Lechler ID an all plastic construction with removable venturi insert. 40 –100 psi range.

 

2.3.3 Sprayer Design

Shields are better at targeting the spray into the grass, reducing drift and increasing deposition. They vary from the simple to the complex. Shielded sprayers allow managers to apply pesticides in variable weather conditions.

 

2.3.4 Sprayer Calibration

Correct calibration will ensure that all the nozzles are discharging the correct amount of liquid at the correct distance and angle to the target and at the correct forward speed.

 

2.3.5 Weather

Wind speed and direction, relative humidity, temperature and atmospheric stability affects drift. Applying the correct product to the correct target at the correct time with the correct equipment is the key to good spraying.

 

2.3.6 Management Strategies to Reduce Drift

Before spraying:

 

1.     Train the operator to use the sprayer correctly under your conditions.

2.     Plan the spraying operation; consider the use of spray instruction cards as a good management tool.

3.     Read and follow the pesticide label.

4.     Select the correct nozzle for the target. Adjust the size and position of the nozzles to achieve correct distribution within the grass canopy,

5.     Consider the use of sprayer nozzles which direct the spray to the target.

6.     Consider spray additives to reduce drift.

7.     Improve spraying logistics to ensure adequate time to spray within ‘ideal’ conditions.

8.     Only spray when weather conditions are ideal; avoid spraying on days when conditions are favorable for atmospheric inversion or wind drift.

9.     Calibrate the sprayer with water to ensure that everything is working correctly.

 

During spraying:

 

1.     Stay alert: ensure the spray is not allowed to drift on to non-target areas and watch for changes in wind speed and direction.

2.     Keep spray pressure as low as possible and ensure an accurate gauge is used.

3.     Maintain a constant speed and pressure.,If an automatic regulator is fitted, remember, small increases in speed result in large increases in pressure.

4.     Avoid spraying near sensitive crops or watercourses; use a buffer zone.