Calibrating Sprayers and Spreaders for Athletic Fields and Golf Courses
Brad S. Fresenburg and Erik H. Ervin
Department of Horticulture
Calibrating sprayers and spreaders is one of the most important steps in
proper application of pesticides for turf pest control. Without knowing how
much spray or granular product is being applied by a sprayer or spreader, an
applicator cannot confidently control a pest with maximum efficacy. The desired
level of control will not be achieved if too little spray solution is applied,
and this results in the need for a second application and additional cost in
time and money. Applying too much spray solution may cause turf injury or present
certain environmental hazards.
This guide will discuss the calibration of hand-held pump-up or knapsack
sprayers, large self-propelled or pull-behind sprayers, drop spreaders and rotary-type
spreaders.
Two basic components
of calibration
The two basic components of calibration, for both sprayers or spreaders, are speed and flow
rate. By knowing both of these components and calculating the proper amount
of pesticide needed, the applicator will consistently get the desired results
of good pest control.
Speed
Speed is simply determined by keeping track of the time it takes to travel a
measured distance. It is best to measure speed in an area that is similar to
the area being treated (e.g., turfgrass with low mowing vs. high mowing). This
is particularly important when the applicator's pace determines the speed with
a hand-held pump-up sprayer, knapsack pump sprayer or spreader. The applicator
should wear the knapsack sprayer half-filled with water or carry a half-filled
hand-held sprayer when calculating speed. The applicator can measure 50 or 100
feet and record the time it takes to walk the distance at a normal pace. Applicators
who use the large-volume handgun sprayers typical of lawn care firms, need to
know their speed also. Use the following formula for calculating speed:
| Speed (mph) = |
Distance (feet) x 60 |
|
| Time (seconds) x 88 |
The speed of an applicator pushing a spreader is not as critical to determine
because the speed is automatically taken into account when setting the flow
rate. However, because different applicators walk at different speeds, applicators
should calibrate their own spreaders. Some products list spreader settings on
the label. Many of these products require that the applicator walk at a specified
speed (e.g., Product M in Brand X spreader at Setting H applied at 3 mph). In
that case, you will need to get some idea of your normal walking pace in miles
per hour. With a spreader (in the closed position) half filled with granular
material, measure the time required to walk a measured distance as described
above.
On self-propelled or pull-behind sprayers, speed is critical for accurate
spraying. Speedometer gauges or electronic LED devices on sprayers and tractors
can give inaccurate readings because of wheel slippage, worn tires or improper
tire pressures. Measure and mark a distance of 100 to 200 feet in level turf
(avoid hills) similar to that being sprayed, and check the time required to
travel the distance. Most accurate measurements will be made with the sprayer
half full of water. Be sure the sprayer is moving at the desired speed when
measuring the time it takes to travel the distance between the starting and
ending markers. The operator can select a gear and throttle setting that are
safe and proper (maintaining minimum boom bounce) and determine what that speed
is. The other option is to select a speed and through trial and error determine
the gear and throttle setting required to achieve that specific speed. Keep
in mind the throttle should be set to full on some equipment for proper operation
of power takeoff equipment. Make several runs and measurements to determine
your speed as accurately as possible.
Flow rate
Flow rate is the amount of solution sprayed through a spray tip in one minute.
The amount of solution, usually measured in gallons per minute (GPM), is determined
by the pressure and the type of spray tip selected. Pesticide labels will usually
recommend spray volumes as gallons per acre (GPA) or gallons per 1,000 square
feet. Flow rates can be calculated by using one of the following formulas:
| GPM = |
GPA x mph x nozzle spacing (inches) |
|
| 5,940 |
or
| GPM = |
gallons per 1,000 square feet x mph x nozzle
spacing (inches) |
|
| 136 |
Selecting spray tips
Hand-held and knapsack sprayers most often have a factory-installed
nozzle. The applicator is then required to calibrate the sprayer with the factory
tip. Some knapsack sprayers have interchangeable standard tips.
Spray tips come in numerous types, angles and materials. Flat fan spray,
full or hollow cone and flood tips are the more common spray tips used in turfgrass
spraying. A flat fan is the most widely used tip and under varying ranges of
pressure is a good selection for many contact and systemic pesticides. Flat
fans (specifically designed for low pressures) offer good spray drift control
when operated at low pressures.
Spray tip material determines the life of the tip, depending on the solutions
sprayed. Brass, nylon, stainless steel, hardened stainless steel and ceramic
offer a selection of spray tip materials with performance ratings that range
from poor to superior, respectively. Keep in mind that superior wear tolerance
usually implies a higher initial price.
Spray angles of 65, 80 and 110 degrees are commonly used in turfgrasses.
Depending on the nozzle type and size, the operating pressure can have a significant
effect on spray angle and quality of spray distribution. Proper nozzle spacing
and height of the boom help achieve optimum spray angles. See your manufacturer's
recommendations for nozzle spacing and boom height.
When selecting a spray tip, find one that will deliver the desired spray
volume and will be the most effective for the type of pesticide application
you are making. Check pesticide labels for recommended spray volumes. Make sure
that all spray tips in the spray boom are of the same pattern, angle and size.
A damaged tip can cause irregular patterns in the spray and should be replaced.
Damaged or worn tips will usually be located when checking the flow rate. If
several tips are damaged or worn, replace all tips with new ones.
Pressure
The applicator is in control of pressure when using hand-held or knapsack
sprayers. The applicator is required to pump the sprayer with air to maintain
adequate spray pressures. The spray pressure on larger spray units is controlled
by pump speed, throttling valve or pressure regulator. Pressures can be regulated
up or down to get the desired flow rate. Higher pressure increases the flow rate
through the nozzle, decreases spray particle size (higher potential for drift),
and increases the rate of tip wear. Therefore, follow the manufacturer's pressure
recommendations for tips selected.
When spray volume and tip selection are determined, the applicator is ready
to start the sprayer and adjust the flow rate.
Calibrating sprayers
Hand-held and knapsack sprayers
It is important to maintain a constant walking speed and spray height when using
a hand-held or knapsack sprayer. Use a left-to-right sweeping motion with little
overlap of the spray for single nozzle wands. Apply just enough solution to wet
the leaf tissue.
Note
Do not saturate leaf tissue or make dripping
wet. This is the biggest mistake made when using hand-held or knapsack sprayers.
Turfgrass injury can result.
To calibrate a hand-held or knapsack sprayer for applying pesticides, first
fill your sprayer with a known amount of water. Spray an area of known size
(e.g., 20 feet x 50 feet = 1,000 square feet). Be sure you keep your spray pressure
up by regularly pumping your sprayer (perhaps a single pump of the handle per
step). After spraying the area, measure the amount of water remaining in the
sprayer. Subtracting the remaining amount of water from the initial amount of
water in the sprayer equals the spray volume per 1,000 square feet (usually
measured in gallons). Then calculate the amount of pesticide required per 1,000
square feet (many labels give rates in ounces of product per 1,000 square feet)
and add that amount of pesticide to the calibrated amount of water to cover
1,000 square feet. If spray area is less than 1,000 square feet, adjust
spray mixture accordingly.
Self-propelled or pull-behind sprayers
Check your spray boom to make sure all strainers are clean and of the same type.
Make sure all tips are the same type, angle and size. Most tips are now color
coded to make this task a little easier. Make sure the tank filter is clean and
free of any blockages.
Fill your spray tank with an adequate amount (half tank) of water to check
flow rate and set pressure. First, turn on your sprayer and check for leaks.
Now is the time to make sure your spray system is working properly and make
repairs as needed. If everything is operating properly, you are now ready to
measure the flow rate.
We will put together an example problem to simplify this procedure.
Use
Worksheet 1 for calibrating your sprayer's flow rate.
Example
If the pesticide label recommends 1 gallon of spray solution per 1,000
square feet or 44 GPA, you can calculate the flow rate in GPM required from
each tip, assuming a speed of 4 mph and a nozzle spacing of 20 inches.
| GPM = |
44 GPA x 4 mph x 20 inches |
= 0.59 |
|
| 5,940 |
Looking at a table for flat fan tips (Spraying Systems, Inc.), you will find
an 8008 tip that delivers 0.57 GPM at 20 pounds per square inch (psi) and 0.69
GPM at 30 psi. The first two digits of the number code on this tip tell you
the angle of the tip is 80 degrees; the last two digits, "08," signify that
0.80 GPM is delivered at a standard pressure of 40 psi.
Turn your spray boom on and adjust the pressure to 20 psi. You can see the
pressure needs to be higher than 20 psi and significantly lower than 30 psi
to achieve the desired flow rate. Keep in mind that the flow rate will increase
as pressure increases, and vice versa. Collect spray from one tip for one minute
in a graduated cup marked in fluid ounces. We can calculate fluid ounces per
minute by multiplying 0.59 GPM by 128 fluid ounces per gallon to equal 75.5 fluid
ounces per minute. Adjust the pressure of the sprayer and continue checking the
flow rate until you achieve the desired rate of 75.5 fluid ounces per minute.
By determining the speed of your sprayer and setting the proper flow rate,
your sprayer is now calibrated to deliver the proper amount of spray solution
per acre. If you are spraying 1 acre of turfgrass, add about half of the required
water to your spray tank. Calculate the correct amount of pesticide required
for 1 acre and add this to the spray tank. Now bring the volume of your spray
tank to 44 gallons and agitate for several minutes.
Driving your spray vehicle at 4 mph will deliver the proper amount of pesticide
at the rate of 44 GPA.
Calibrating spreaders
When calibrating spreaders, it is recommended to calibrate the spreader for half
the rate desired. Applications of fertilizers or pesticides will be more evenly
distributed if applied in two directions (x or + pattern). This also helps in
preventing the striping patterns evident in poor application techniques where
proper overlap was ignored. Therefore, calibrating for half the rate allows for
applications in two directions giving a full rate of fertilizer or pesticide.
Drop spreaders (Worksheet 2)
Calibrating drop spreaders can be completed two different ways. Some drop spreaders
have collection pans for catching dropped material, usually attaching to the
bottom of your spreader. If your drop spreader does not have a collection pan,
it is easy to make one and attach it with bungee cords. The collection pan should
be oversized to collect all material dropped, but not very deep. This allows
the pan to hang between the bottom of the spreader and the ground.
Method #1
First, determine from the product label the amount of granular pesticide,
granular fertilizer, or a combination product you require per 1,000 square feet.
Measure the width of your spreader in feet. Divide 100 by the width of your spreader
and measure this distance with markers. (Example: 100 divided by 1.5 feet [18" wide]
= 66.67 feet). The area measured represents 100 square feet, or one-tenth of
the 1,000 square feet for one swath. Fill your spreader with the material you
wish to calibrate. Set your spreader to the manufacturer's recommended setting
or a midsize opening. Push the spreader at a normal pace in an area similar to
that being treated, turning the spreader on and off for the distance marked.
Weigh the material collected, which should equal one-tenth of the material required
for 1,000 square feet. Adjust spreader and make several runs until the desired
amount is collected.
Method #2
The second method requires the applicator to push the spreader over
a collection pan or box (1 foot by the width of the spreader) on a smooth surface.
A spreader that drops an 18-inch swath will require a collection box 1 foot x 1.5 foot
(1.5 square feet). The applicator needs to know the amount of material required
for one square foot. Set your spreader to the manufacturer's recommended setting
or a midsize opening. You can make several passes over the collection box, in
the same direction, to collect enough material to weigh. Check the distribution
of material in the collection box to make sure an even amount of material is
dropping across the entire width of the spreader. If material is falling unevenly,
make sure there are no blockages in the bottom of your spreader. Divide the weight
of the collected material by the number of passes, then divide by the number
of square feet in the collection box. The result should be the amount of material
required for one square foot. Adjust spreader and make several runs until the
desired amount is collected. Be sure to clean-up all materials that fall outside
of the collection box.
Rotary-type spreaders (Worksheet 3)
Some cyclone spreaders have collection pans that can be attached around the spreader
to collect all material thrown. Follow the first procedure for drop spreaders,
if you have a collection unit. However, this does not allow you to determine
the effective swath and overlap required. The following procedure calibrates
the spreader for the material being used and determines how much overlap is needed.
Calibrating a cyclone spreader without a collection unit will require you
to construct a series of collection pans or boxes 1 foot x 1 foot x 3 inches high (usually
11 to 13 boxes). This method also requires that the calibration be done on a
smooth surface, because the actual material (granular pesticide or fertilizer)
must be used. This allows you to cleanup any material that is thrown outside
of the collection boxes.
Set the collection boxes in a row, side by side, allowing room in the middle
for the spreader to pass over one box and leaving space for the tires to pass
by (Figure 1).
Figure 1
Determine how much material the spreader deposits in each
of 11 1-foot-square boxes. Calculate the distribution of material and adjust
overlap of successive passes to achieve even coverage. The distribution shown
here requires an overlap of 2 feet.
Determine how much material is required per 1,000 square feet from the
product label. Divide this amount by 1,000 to calculate the amount of material
required for one square foot.
Set the spreader to the manufacturer's recommended setting or a midsize opening.
Make several passes over the collection boxes, in the same direction, to
collect enough material in each box for weighing. Divide the weight of the material
collected in each box by the number of passes to equal the average amount of
material thrown per square foot in each pass. Adjust the spreader and make several
runs until the desired amount is collected.
Record the amounts of material from each box to see if you have an even distribution
across the swath. Typically, there should be less material in the outer boxes.
This determines how much overlap is required. For example, if the boxes contain
the percentages of required material shown in Figure 1, then overlap should
be 2 feet.
If your spreader throws more material to one side than the other, then the
pattern plate at the bottom of your hopper should be adjusted. You may need
to adjust your overlap if your spreader does not have a pattern adjustment and
make all applications in the same direction. As always, be sure to cleanup all
materials that fall outside of the collection boxes.
Again, an additional recommendation we make for spreader calibration, is
to calibrate materials for half the amount required per one square foot. Then
apply material in two directions (x or + pattern) for better distribution and
elimination of striping.
Any applicator who becomes familiar with these calibrating procedures can
make proper pesticide and fertilizer applications to achieve the best in pest
control and plant growth.
For further information
- TeeJet Spray Products, Catalog 73, Spraying Systems Company, Wheaton, Illinois.
- Calibration of Pesticide Application Equipment for Golf Courses and Recreational
Turf, video produced by Marathon Ag/Environmental Consulting, Las Cruces,
New Mexico.
Note
The mention of any spray tip type, spreader type or brand name does not
constitute an endorsement of that type or brand. The University of Missouri
does not recommend one brand of spreader, spray equipment or parts over another.
Sprayer Calibration (Worksheet 1)
Determine
Gallons desired ________ per acre; ________ per 1,000 square
feet
mph:________ Nozzle spacing:________ inches
Use
| GPM = |
GPA x mph x nozzle spacing (inches) |
|
| 5,940 |
or
| GPM = |
galllons per 1,000 square feet x mph x nozzle
spacing (inches) |
|
| 136 |
GPM = ________
Look to manufacturer's guide for tip selection:Spray tip selected
________ GPM:________ PSI:________
Check flow rate:Starting pressure
________
- Trial 1
- Fluid ounces collected ________ per minute
divided by 128 = ________ GPM
Adjust pressure up or down as needed.
- Trial 2
- Fluid ounces collected ________ per minute
divided by 128 = ________ GPM
Adjust pressure up or down as needed.
- Trial 3
- Fluid ounces collected ________ per minute
divided by 128 = ________ GPM
Adjust pressure up or down as needed.
- Trial 4
- Fluid ounces collected ________ per minute
divided by 128 = ________ GPM
Adjust pressure up or down as needed.
Sprayer Calibration (Worksheet 2)
Drop spreader -- Method #1
Determine
Amount of product required ________ ounces; ________ pounds per 1,000 square feet
- Take 100 divided by the width (________ feet) of the spreader and measure
this distance (________ feet) with markers to equal 100 square feet (one-tenth
of 1,000 square feet).
- Close spreader, attach collection pan, fill spreader with material being
calibrated.
- Set spreader on manufacturer's recommended setting or midsize opening.
- Push spreader at a normal pace turning the spreader on and off for the
distance marked.
- Trial 1
- Material collected ________ ounces or ________ pounds x 10 = ________ ounces or pounds per 1,000 square feet
Adjust opening.
- Trial 2
- Material collected ________ ounces or ________ pounds x 10 = ________ ounces or pounds per 1,000 square feet
Adjust opening.
- Trial 3
- Material collected ________ ounces or ________ pounds x 10 = ________
ounces or pounds per 1,000 square feet
Adjust opening.
- Trial 4
- Material collected ________ ounces or ________ pounds x 10 = ________
ounces or pounds per 1,000 square feet
Continue until the desired amount of product is collected.
Determine
Amount of product required ________ per square feet
- Close spreader, put collection box in place, fill spreader with material
being calibrated.
- Set spreader on manufacturer's recommended setting or midsize opening.
- Push spreader over the collection box at a normal pace.
Trial 1
| Material collected (pounds or ounces) |
= |
________ pounds or ounces |
= ________ per square feet |
|
|
| Area of collection box (square feet) x Number of passes |
________ square feet x ________ passes |
Adjust opening.
Trial 2
| Material collected (pounds or ounces) |
= |
________ pounds or ounces |
= ________ per square feet |
|
|
| Area of collection box (square feet) x Number of passes |
________ square feet x ________ passes |
Adjust opening.
Trial 3
| Material collected (pounds or ounces) |
= |
________ pounds or ounces |
= ________ per square feet |
|
|
| Area of collection box (square feet) x Number of passes |
________ square feet x ________ passes |
Adjust opening.
Trial 4
| Material collected (pounds or ounces) |
= |
________ pounds or ounces |
= ________ per square feet |
|
|
| Area of collection box (square feet) x Number of passes |
________ square feet x ________ passes |
Adjust opening. Continue until the desired amount of product is collected.
Sprayer Calibration (Worksheet 3)
Rotary-type spreader
Determine
Amount of product required ________per square feet
- Layout collection boxes side-by-side on smooth surface in the above pattern.
- Set spreader on manufacturer's recommended setting or mid-setting.
- Make several passes over the collection boxes, in the same direction,
to collect enough material in each box for weighing.
Trial 1
Material collected -- ounces, grams, etc.
Divide amount collected by the number of passes and record.
Adjust spreader and run again.
Trial 2
Material collected -- ounces, grams, etc.
Divide amount collected by the number of passes and record.
Adjust spreader and run again.
Trial 3
Material collected -- ounces, grams, etc.
Divide amount collected by the number of passes and record.
Continue until the desired amount of product is collected.
G6751, new May 2000