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Boom sprayers are commonly used to apply pesticides to control weeds, insects and diseases. But finding the balance of spray coverage and efficacy while limiting off-target movement can be a challenge.

Brad Haire, Executive Editor

June 23, 2020

4 Min Read
Farm Press

Farmers apply pesticides efficiently and wisely each year. But due to a recent court decision regarding the use of popular herbicides, this is the season to fine-tune the sprayer to get the most out of each application.

Earlier this month, Simer Virk, University of Georgia research engineer who specializes in precision agriculture machinery systems, sent Southeast Farm Press recommendations growers can use to get the most of out of their boom sprayers and pesticide applications in 2020. Virk worked in collaboration with Wes Porter, UGA Extension precision ag specialist, and Eric Prostko, UGA Extension weed specialist.

Boom sprayers are commonly used to apply pesticides to control weeds, insects and diseases. But finding the balance of spray coverage and efficacy while limiting off-target movement can be a challenge.

To keep it all in line and up to the task, the UGA Extension specialists recommend growers consider:

Nozzle Selection

Correct nozzle selection is one of the most important decisions related to pesticide applications. Nozzle type affects product rate, uniformity, coverage and drift. Check pesticide labels for recommended application rate and conditions needed to safely apply the pesticide. Consult the manufacturer’s nozzle catalog for selecting the nozzle that provides the desired output, or flow rate and droplet size, specific to the application. Nozzle selection will also depend on the ground speed and pressure required to achieve the rate in gallons per acre. A TeeJet catalog illustrating different nozzle types with their flow output, droplet size, rate at different speeds can be accessed here.

Spray Pressure

Remember, lower pressures result in larger droplets. Higher pressures produce smaller droplets. For most applications, maintain a spray pressure that results in medium to coarse droplets to reduce drift and obtain adequate spray coverage.

Ground Speed

A higher travel speed will require a higher nozzle flow rate to achieve the given application rate and vice-versa. Reduce the sprayer speed, or less than 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 potential for drift.

Boom Height

Lower boom height is generally recommended for maintaining a proper spray pattern and overlap. Make sure to use nozzles that have a 110-degree angle to allow spraying at lower boom heights without effecting spray coverage. Follow nozzle manufacturer recommendations for boom height, generally 24 inches or less for 20-inch nozzle spacing, to achieve satisfactory coverage and reduce drift.


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 increase drift especially at higher boom heights. Avoid pesticide applications when conditions for temperature inversions are favorable. Also, consult labels for optimum time of day applications. For example, current dicamba product labels recommend applications between one hour after sunrise and two hours before sunset to help reduce off-target issues.

Sprayer Calibration

There are several methods for calibrating boom sprayers; however an ‘ounce’ or ‘1/128 acre’ is the one, most commonly used and recommended for calibrating a boom sprayer. The method is based on spraying 1/128 of an acre per nozzle and collecting the spray output from each nozzle for the time it takes to spray the area.

Since there is 128 ounces in one liquid gallon, this convenient relationship results in ounces of liquid collected equal to the application rate in gallons per acre. A detailed step-by-step guide on this calibration method can be found on UGA Extension website.

Spray Technology

Application rate (gallons per acre) is dependent on ground speed, pressure, and nozzle output, any changes in ground speed would require a change in flow rate to meet the desired rate. Rate controllers perform flow rate adjustments based on changes in ground speed during spraying and help maintain application rate and coverage throughout the field.

The use of rate controllers also helps improve spray application by minimizing skips and overlaps within a field. Advanced technologies such as PWM (pulse width modulation) nozzle technology and automatic boom height control are also currently available for use on spraying equipment for better application and drift reduction. Spray technology can be utilized to minimize variations in application rate and coverage as well as maintain a record of spray application including product, rate, pressure, nozzle type etc. used in each field.              

Dicamba Ruling

A court ruling June 3 vacated the registrations of Xtendimax, Engenia and FeXapan. An EPA decision followed which allows growers who had product in possession June 3 to apply the products through July 31, following labelled usage.

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