Southeastern U.S. Vegetable Crop Handbook - 2022 - 134

Calibrating Chemical Application Equipment
PURPOSE
To determine if the proper amount of chemical is being applied,
the operator must measure the output of the application equipment.
This technique is known as calibration. Calibration not
only ensures accuracy, a critical factor with regard to many
chemicals, but it can also save time and money and benefit the
environment.
GETTING STARTED
Careful and accurate control of ground speed is important for
any type of chemical application procedure. From large self-propelled
sprayers and spreaders to small walk-behind or backpack
units, precise ground speed is a key for success. Ground speed
can be determined by one of two methods. The first method requires
a test course and stopwatch. For this procedure, measure
a suitable test course in the field and record the time it takes to
cover the course with the equipment. The course should be between
100 and 300 feet long. Drive or walk the course at least
twice, once in each direction and average the times for greater
accuracy. Calculate the speed with Equation 1 below.
Equation 1. Ground Speed (MPH) =
Distance x 60
Seconds x 88
The second method is to use a true ground speed indicator such
as a tractor-mounted radar or similar system. Do not rely on
transmission speed charts and engine tachometers. They are not
accurate enough for calibration.
CALIBRATING A SPRAYER:
PREPARING TO CALIBRATE
For calibration to be successful, several items need to be taken
care of before going to the field. Calibration will not be worthwhile
if the equipment is not properly prepared. Whenever possible,
calibration should be performed using water only. If you
must calibrate using spray mixture, calibrate the equipment on a
site listed on the chemical label and with wind speeds less than
5 MPH. Follow the steps outlined below to prepare spraying
equipment for calibration.
1. Inspect the sprayer. Be sure all components are in good
working order and undamaged. On backpack sprayers,
pay particular attention to the pump, control wand, strainers,
and hoses. On boom sprayers, pay attention to the
pump, control valves, strainers, and hoses. On airblast
sprayers, be sure to inspect the fan and air tubes or deflectors
as well. Be sure there are no obstructions or leaks in
the sprayer.
2. Check the label of the product or products to be applied
and record the following:
* Application Rate, Gallons per Acre (GPA)
* Nozzle Type, droplet size and shape of pattern
* Nozzle Pressure, Pounds per Square Inch (PSI)
* Type of Application, broadcast, band, or directed
3. Next, determine some information about the sprayer and
how it is to be operated. This includes:
* T ype of Sprayer: backpack, boom, or airblast. The
type of sprayer may suggest the type of calibration
procedure to use.
* Nozzle Spacing (inches): for broadcast applications,
nozzle spacing is the distance between nozzles.
* Nozzle Spray Width (inches): For broadcast applications,
nozzle spray width is the same as nozzle
spacing-the distance between nozzles. For band
applications, use the width of the sprayed band if the
treated area in the band is specified on the chemical
label; use nozzle spacing if the total area is specified.
For directed spray applications, use the row spacing
divided by the number of nozzles per row. Some
directed spray applications use more than one type
or size of nozzle per row. In this case, the nozzles on
each row are added together and treated as one. Spray
width would be the row spacing.
In most cases, a backpack sprayer uses a single nozzle.
Some sprayers use mini-booms or multiple nozzles. The spray
width is the effective width of the area sprayed, being sure to
account for overlap. If you are using a sweeping motion from
side to side, be sure to use the full width sprayed as you walk
forward. If you are spraying on foliage in a row, use the row
spacing. Dyes are available to blend with the spray to show what
has been covered.
* Spray Swath (feet): The width covered by all the nozzles
on the boom of a sprayer. For airblast or other boomless
sprayers, it is the effective width covered in one pass
through the field.
* Ground Speed, miles per hour (MPH). When using a
backpack sprayer, walk a comfortable pace that is easy to
maintain. Slow walking speeds will take longer to complete
the task while high speeds may be tiresome. Choose
a safe, comfortable speed that will enable you to finish
the job in a timely manner. On tractor-mounted sprayers,
select a ground speed appropriate for the crop and type of
sprayer used. Slow speeds will take longer to complete
the task, while high speeds may be difficult to control and
unsafe. Choose a safe, controllable speed that will enable
you to finish the job in a timely manner. Ground speed can
be determined from Equation 1.
134
2022 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2022

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