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Spray Considerations for Effective Pesticide Applications

Effective pesticide applications are needed to stay on top of weed, insect, and disease control throughout the growing season. Achieving both the desired spray coverage and efficacy while keeping off-target movement of pesticides to a minimum is a very challenging but an important task. Applications resulting in under- or over-application of pesticides, ineffective coverage, and/or off-target movement can have serious consequences. Below are several things to consider to help keep the product on target when applying pesticides safely and efficiently with boom sprayers:

Timeliness:  Being on time with pesticide applications is the most important factor in determining the success of any pesticide application.  Late application usually will require higher use rates or split applications and are more often than not, less effective. 

Nozzle Selection: Check pesticide labels carefully for recommended application rate, droplet size, and any other conditions needed to safely apply the pesticide. Based on the application type and pesticide mode of action, select the nozzle that provides both the desired output (in gallons per acre or GPA) and the droplet size. Nozzle selection will also depend on the ground speed and pressure required to achieve the desired GPA.

Spray Pressure: Spray pattern and droplet size changes with spray pressure. Lower pressures result in larger droplets whereas higher pressures produce smaller droplets for a given nozzle size. Based on the application (whether coverage or drift control is necessary), consider selecting a nozzle that provides the required droplet size in the 30 – 50 PSI pressure range. Spray operation at both excessively low and high pressures results in non-uniform spray angle and pattern.   

Ground Speed: Application speed plays an important role in achieving the desired application rate. A higher travel speed will require a higher nozzle flow rate to achieve the given application rate and vice-versa. It is recommended to reduce the sprayer speed (<10 MPH) to obtain a consistent and more uniform coverage. Faster speeds will cause excessive boom bounce and spray inversion sending finer droplets higher in the air and increasing drift potential.

Boom Height: Boom height influences overlap and uniformity of spray application at a selected nozzle spacing and spray angle. Lower boom height (20 – 30 inches from the target) is generally recommended for maintaining a proper spray pattern and overlap to achieve satisfactory coverage while reducing drift. Make sure to use nozzles that have a 110° angle to allow spraying at lower boom heights without affecting spray coverage.

Environment: Weather conditions such as wind speed and temperature also play a role in achieving the desired spray coverage and on-target application. High wind speed affects spray coverage and also results in greater drift. Wind direction should be also considered to avoid spraying towards sensitive crops, homes, etc. Warmer temperatures also increases drift especially at higher boom heights. To minimize off-target movement, avoid pesticide applications when conditions for temperature inversions are favorable. Inversions typically occur later in the day and may persist until early in the morning.

Sprayer Calibration: Proper sprayer calibration is important to verify the nozzle output (gallons per minute) and consequently application rate (GPA) based on the selected ground speed and nozzle spacing. During calibration, make sure to check the application uniformity across the entire boom, and perform a thorough sprayer inspection to ensure proper functioning of all sprayer components.

Spray Technology: Consider using spray technologies such as a rate controller, and section or individual nozzle control which helps in maintaining application accuracy across the whole field by minimizing off-target applications. Advanced technologies such as pulse width modulation (PWM) technology and automatic boom height control are also currently available for use on boom sprayers for better application control and drift reduction.